CCD Issues --Page 4

       

Subject: Making CCD Flats w/Light Box

From: Gregg Ruppel <ruppelglSLU.EDU>

I use a light box for all of my images. Very important because I shoot from a rather light polluted suburban location. You can see a picture of my homemade light box (modeled after one designed by Al Kelly) at: <http://www.biz1.net/~ruppelgl/observatory.htm>
    Note: should open a new browser window over this one.

The light box is at the bottom of the page. Mine is made from 1/4” foam board and duct tape, with four mini-lamps and a 9V battery.

My light box is made from foam board. I made a cube 15” on a side; the box should be slightly larger than the OTA (mine is a 10” LX200). The “lid” of the box has a hole cut into it the exact size of the optical tube. Recessed about 2” inside the lid is the diffuser, which in this case is a piece of thin Styrofoam (1/8”) packing material sandwiched between two layers of clear acetate. The acetate (you could use thin Plexiglas) just helps keep the diffuser material flat. I just used some pieces of foam board to form a square around the hole for the OTA. Of course everything is held together with duct tape. See the crude illustration below:

 ________________________
| |
| |
| | box
| |
 diffuser
 __________________
_x_| |_x_ lid with lamps (x)
 OTA goes here 

The minilamps are wired around the diffuser flat against the inside of the lid; the 9V battery and a push button switch is mounted on the outside of the lid. When the lid is placed on the box, the lamps illuminate the diffuser indirectly by bouncing their light off the inside surfaces of the box. The foam board is translucent enough that it can be used during twilight without using the internal lights. You can also see some directions on Al Kelly’s web page at:

<http://www.ghg.net/akelly/taking.htm#8>
    Note: should open a new browser window over this one.

Subject: Photons per ADU    

From: Chris Frye <cfrye44impop.bellatlantic.net>

I called my CCD camera's manufacturer, not Meade, and they told me the equation for calculating the Photons per ADU is as follows:
    P/ADU = Full-Well Capacity /2^N. Where N is the image depth in bits.

In the case of the 416XTE,
    N = 16 bits and, according to the Meade web site, Full-Well Capacity = 85,000.

Therefore: P/ADU = 85,000 / 2^16 = 85,000 / 65,536 = 1.3

Subject: LX200 CCD Image Magnification    

From: Douglas Benn

While an effective magnification can be calculated in this case (because the math allows you to plug the appropriate values into the appropriate formulae), the real issue in photography is field of view. Technically, a pure magnification figure is undefined, since you are taking an image that can be resized anyway, and if you're not using an eyepiece, you aren't "magnifying" the image at the focal plane anyway. No, there is no eyepiece in the 416. :-) Trust me, I have one.

Coupling the camera directly to the scope yields a field of view based on the size of the chip and the focal length of the scope, as well as the size of the pixels. This type of hookup is referred to as "prime focus," and the formulae for calculating your field of view are as follows:

1. Calculate the # of arcseconds per pixel; equation is (size of pixel in um / focal length in mm) * 206.265
2. Multiply the above value by the number of pixels in the X direction and the Y direction on the chip, to give you the X and Y fields of view (in arcseconds)
3. Divide both values from #2 by 60 to give yourself arcminutes, if you so desire. The trick is in knowing the focal length at the image plane. It is not necessarily 2500 mm - especially with an SCT which uses a moving primary and a magnifying secondary. It is 2500 mm at a very specific distance from the back of the scope, but if you go further back or closer in, it changes. The only precise way to measure the real FOV is to take a picture of a double star of known separation, or a perfectly focused image of a clean disk of known size (like Jupiter, etc.) and count pixels. Then, you can solve the equation "in reverse" for your actual focal length and effective f/ratio.

Either way, you can calculate an "apparent magnification" of sorts if you like, once you know the true focal length at the image plane. I have seen this done two ways:

1. Knowing your real field of view, plug this and an apparent field of view of 1 Radian (57.295779 degrees) into the equation usually used to calculate eyepiece actual FOV using magnification and apparent FOV. (True field in arcminutes = 3D apparent field in degrees * 60 / magnification).
2. Knowing your real focal length, use the hypotenuse of your chip in mm as if it were an eyepiece (Magnification =3D focal length in mm / hypotenuse of chip in mm). Personally, I avoid both and just talk in terms of FOV.

Subject: LX200 & ST-7E/ST8E Guide Chip    

From: Bruce Johnston Date: Oct., 2000

I realize that this idea may be old hat, but just in case, I thought I’d pass it along. If you’ve found an object that you want to shoot but you then have trouble locating a decent guide star, this idea may help in locating one that’s near the chip and you don’t know it. Do this series of steps sometime before you are going to shoot images. I use CCDOPS for DOS, but it would be true for any camera control program, I think.

1. Center a nice, bright star in your imaging chip, such as Altair or Vega, etc.
2. Slowly move the scope until that same bright star ends up in the center of the guide chip. For my setup, I have to move the scope NORTH about 6 arc minutes to move the star down to the guide chip.
3. Center the bright star on the guide chip.
4. Switch your display on the LX200 to display the RA and DEC of where you’re located in the sky. Write it down.
5. Move the star back to being centered on the imaging chip. (In my case, it means moving the scope back South.) Write down the coordinates.
6. The difference in the DEC and RA can be now used for looking at a larger field for a guide star.
7. What you do is, center the object you wish to shoot on the imaging chip as usual.
8. To see the general field where the guide chip is, move the scope in the OPPOSITE direction by the difference in the amount you just got. (In my case, I move my scope SOUTH by about 6 arc minutes).

You can then see a much bigger area around where the guide chip will be located, to see if there’s a decent guide star just out of the field of view.

Subject: F/3.3 Focal Reducer Lessons    

From: James McMillan, Date: Feb., 2001

About a month ago, I asked MAPUG for - and received - help getting my F/3.3. focal reducer to work correctly with my LX 200 f/10, 416XTE and 616 color filter wheel. I thought I'd report back on my progress.

Interestingly, my problem turned out to be a defective F/3.3 focal reducer. I originally purchased it in October, 2000. Images taken with it had distorted stars (coma) over about 1/3 of the image, so I returned it for another - no problems with the mail-order company I purchased it from. The second F/3.3 performed exactly the same as the first. That's when I wrote to MAPUG for help. I tried all the suggestions, but to no avail. I began worrying that I had some other optical problem with the scope. So, I checked with Meade (Amy). She said this was the first she's heard of coma problems with the F/3.3 and my combination of equipment. We wanted to absolutely rule out that the F/3.3 was at fault, so we replaced the F/3.3 again. The third F/3.3 focal reducer works great. I now have round stars throughout the image.

I do have a couple of lessons learned I'd like to share:

1. Since my scope performed well at f/10 and f/6.3, the obvious place to look for the problem was with the F/3.3 focal reducer. While it took 3 tries to confirm that, it paid to continue to work on the obvious.
2. Focus is critical to achieving good, round stars throughout the image.
3. Meade was very responsive helping me.
4. There is quite a bit of vignetting - about 8000 difference between the center and edges of the image - but a good flat field will eliminate it.
5. I built a light box (1 evening project) and have had great success using it. It's almost mandatory when using the F/3.3.

Subject: Re-Assembling a f/3.3 Focal Reducer   

From: Duncan Miller <duncdmiller.demon.co.uk> Date: Jul 2005

"....dropped it on the floor. Nothing broke, but I have no idea how to assemble all of the lenses and spacers. Has anyone in the group ever taken one of these apart and put it back together successfully, or is there an online diagram of the Meade f/3.3."

There is a diagram available if you follow the link at the bottom right of this page:
    <www.meadelx200gps.com/tips.html>

Subject: CCD Imaging-- Single Exposure vs. Stacking    

From: Radu Corlan <rcorlanprofis.ro>

Ed Registrato wrote:
> Which image will yield the greatest amount of stars and have the faintest
> magnitude stars on the image at the end...
>
> 1. A single auto guided image taken with a CCD for 15 mins...
>   Or
> 2. A stacked imaged consisting of 15 one min. images.
>
> Assume all equipment is the same, the locations are the same, the images are
> taken at the same time, etc, etc.... The only variable is how long the CCD
> exposure is. Drift is not a factor here.
>
> The question is which image (1 or 2) will yield more stars???? Why???

The CCD chip is linear (at least at the lower light levels). This means that the total number of counts / pixel you get is the same in both situations. However, the ability to detect a faint star depends on the how much noise you have in the rest of the image. There are three main sources of noise in a CCD: readout noise, photon shot noise and dark current shot noise.

Readout noise is added to the image whenever the chip is read out - it's independent of the integration time. A very typical value will be 10 electrons RMS. Assume an image that is totally unexposed. When read, this image will show the readout noise. If you add several such exposures together, the noise adds as RMS (root of the mean of the squares). So, if the readout noise is 10 electrons, if you stack two images the noise will be 14.4 electrons, four images will give you 20 electrons and so on.

If we apply this to your situation, if you had a faint star that gives you a count of 2.5 electrons/minute, with 16 1-min exposures you will get a count of 40 electrons for the star, and a noise of 40 (10 * sqrt(16)) electrons for the background. A SNR of 1, which makes it pretty difficult to detect the star.

If you had a single 16-min exposure, you would have the same 40 electrons count for the star, but only 10 electrons of noise on the background. This gives you a SNR of 4, making it much easier to detect the faint star.

>From the point of view of readout noise, one exposure is much better than many.

Now let's consider shot noise. When electrons are generated on the chip, which can happen because of exposure to light or because of thermal effects (so-called dark signal), the count of these electrons does not rise at a constant rate. Rather, it follows the Poisson distribution. Light itself is noisy.

How noisy? For a count of N electrons, the noise signal (or in other words, the uncertainty of that count) is sqrt(N). So, if you expose an image to a uniform light level of 100 electrons (average), such as the sky glow, and you subtract the average level, you are left with a noise of 10 electrons (sqrt(100)).

Let's see how this noise stacks up with multiple exposures.

Say you get an average of 16 electrons / minute of sky glow exposure. Then with the single exposure, you have a total of 256 electrons of sky exposure. This contributes with 16 electrons of noise (= sqrt(256)). The 16 individual exposures each contribute with a shot noise of 4 electrons (4 = sqrt(16)). They add up as RMS, so the total shot noise contribution of the 16 exposures is again 16 electrons. This shows that from the point of view of the shot noise, it's equivalent if you make several short exposures, or a single long one. Thermally generated electrons follow the same statistic as the light-generated ones, so the same applies to the dark signal.

Now, if you have a very long exposure, the readout noise will be insignificant compared to the background shot noise. We say that the exposure is shot noise dominated (it could be sky dominated or dark current dominated).

For shot noise dominated exposures, it is equivalent to have one long exposure, or several short ones. In this case, it's usually preferable to have several short ones, because: some tracking errors can be compensated by shifting the image before stacking; there is a lower probability of having cosmic ray hits; less change of a bright object ruining blooming the chip; there is a lower probability of something (airplane, cloud, bump on tripod) ruining the exposure.

When does the total SNR begin to degrade with shorter individual exposures? When the readout noise becomes dominant - that is, when the dark signal + sky exposure equals the readout noise.

Subject: Stacking CCD Images vs. Longer Exposures    

From: Radu Corlan <rcorlanpcnet.ro>

Don Tabbutt wrote:
> Stacked exposures can also increase signal to noise ratio appreciably. This
> is because the signal is generally the same on each "short" exposure, while
> the noise is random from exposure to exposure. As the images are added in
> the stacking process, the signal gets stronger and stronger, while the noise
> remains about the same, since it is such a random pattern, and thus doesn't
> get added linearly like the signal does. This gives an end result with a
> signal to noise ratio approximating that of an equivalent long exposure, but
> with much tighter star images.

There seems to be some confusion in this area; in fact, things are pretty simple. When you add up two uncorrelated sources (like the noise in two 'short' exposures, you end up with a level that is the square root of the sum of their squares; in particular, when N sources have the same noise (say N 1 sec exposures), the noise of their sum will be sqrt(N) times larger. The 'signal' correlates between the two, and will be N times larger (of course, if it's still not saturated).

So, while by doubling the exposure time you double the signal/noise ratio, by stacking two exposures of the same total length, you increase the SNR by just sqrt(2) (about 1.4 times).

This situation holds while the noise of each image remains the same irrespective of the exposure time. Two main factors prevent it to be so:

• the thermally generated signal (dark current) and
• the sky background.

While we think of the dark current as some constant value that is multiplied by the exposure time, things are not exactly so; if we had a camera that has zero readout noise (and so would give exactly the same counts for each pixel for a number of images) if we allow some dark current to accumulate, the counts will start to differ between the successive frames - there is some noise associated with the dark current. Even if we subtract a dark frame, we will still see the effect of this noise.

How large is this noise? The most important contributor to it is shot noise, whose cause is the discrete nature of electric charge. It can be shown that the RMS value of it (in electrons) is the square root of the total number of electrons in the dark current. The background sky exposure behaves exactly in the same way: it introduces a noise that is the sqrt of the number of electrons generated.

Now, let's assume that the readout noise is negligible, and we want to determine the influence of stacking vs. long exposures on the dark current noise. If we take two exposures of t seconds, the dark current signal will be DC * t, and the noise associated with that is sqrt(DC * t). DC is the dark current (in electrons / second).

For the stacked image, the noise will be the RMS sum of the two:
Nstack = sqrt (sqrt(DC * t) ^ 2 + sqrt(DC * t) ^ 2) = sqrt (2 * DC * t).

We see that this is exactly the same as the noise associated with an exposure that lasts 2 * t.

So, with regard to dark current noise (and sky background noise), a longer exposure has no advantage over a number of stacked exposure of the same total length. In the presence of both readout noise and dark current noise, it makes sense (from a SNR point of view) to increase the individual exposure times only until the dark current + sky background noise becomes comparable to readout noise (or in other words, the sky background + dark signal level becomes comparable to the square of the readout noise - both expressed in electrons).

Sorry for the lengthy and rather incoherent post; there is much confusion about this subject, and it's not easy to express things in words.

Subject: SBIG STV Experiences --part 1 of 2   

From: Glenn, Date: Feb 2001

Its real easy to get started with the STV but depending on your interests it may not take you as far as other cameras for the price.

If you are interested in using the STV as an autoguider, it appears that there is nothing better on the market but there are cheaper options (like the ST4) that work well.

If you are interested in video, there are cheaper solutions for planets and Moon but none allow the ability to capture faint objects. Not only does the STV allow for long integration times but it also has "track and accumulate" built in.

If you are interested in planets, the electronic shutter is really great since it allow for very short exposure times (in msecs) and produces no vibration. It also has a built in ND filter to reduce the brightness of objects like the Moon, Sun, and Venus that would saturate the chip even at the shortest exposures. Downside is that a color wheel and tricolor support in the software is not available. It was designed to be B&W and to get color will require your own creative solution.

If you are interested in deep-sky, the STV will produce recognizable images very easily. They even present well in group settings like public star parties. However, the pixel count is low for the price by today's standards, it is not 16bit (12 max I think?), and again the lack of color support is a drawback.

It is A LOT of fun! The video capabilities open might lend itself to some interesting projects. My current obsession is to image MIR with it using the satellite tracker software and my 12" LX200 before it falls out of the sky. The ISS is also on the list but I don't have a deadline for that one.

I have some initial images I've taken from my VERY light polluted skies here in Beaverton, OR.

    <http://www.geocities.com/sue_and_glenn/>
     Note: should open a new browser window over this one.

------------------------------------

Subject: SBIG STV Experiences --part 2 of 2   

From: Bert Katzung <katzung1home.com>

Glenn has a very complete response to your question. In addition, I would suggest that you subscribe to, or at least look at, the SBIG user group at:

<SBIGyahoogroups.com>

There has been a ton of stuff there on the STV and its capabilities (confirming Glenn's comments).

Subject: Lightbox Drawings and Details    

From: Gregory Pyros <gpyroshome.com>

After receiving many requests for my CCD light box drawings, I translated the drawings to a PDF file and added some photos so anyone interested can easily build one, and put it all up on my astro web site for one and all.

Mine was designed for my 10" LX200 f/10, but with a few minor changes it can be modified for any size scope. In addition, I also built an adapter so that you can also use it if you sometimes use your CCD with a 35mm camera lens, and the details for that are included, also. It is made of 0.25" foamcore, and the entire unit weighs only 2.5 pounds.

Click here for my general customizations page, then click on the picture of the lightbox to go to the page with the details.

    <http://www.pyros.com/greg/html/customizations.html>
    Note: should open a new browser window over this one.

Subject: Which LX Scope Best for Imaging? --part 1 of 2   

From: Doc G

Jim Henson wrote:

> >As a visual instrument the 12" is great. But as an imaging platform it isn't.
> >Gene Horr
>
> What is wrong with the 12" for imaging? Jim

Gene and I have been involved on MAPUG for many years now and his comment, with which I generally agree, is woven into the folklore of the LX scopes.

The issue is basically this. The three LX scopes (8, 10 and 12 inch) all have the same base and drives. I have had all three. Some years ago I made measurements on the 10 and 12 inchers. The 12 inch scope seemed (through mechanical measurement) easier to set into oscillation and vibrated longer than the 10 inch scope. This is because the mass of the 12 inch OTA is greater than that of the 10 inch OTA. Everything else being similar, the greater mass oscillates longer. The 12 inch scope is also larger in surface area and is thus more easily disturbed by air gusts and the like. The differences are small, but for very critical imaging, any instability will spoil the image since the images are taken over a long time period.

After my report and even during this time frame (several years ago) numerous serious imagers have reported more difficulty imaging with the 12 inch scope than with the 10 inch scope.

That is not to say that excellent images cannot be had with the larger scope. But additional care is required. The scope must not be disturbed at all during exposures. It should be protected from the wind very carefully. Even the action of the guider in adjusting the rate of the motors can be a disturbance to the OTA. The chattering of the motors can also be a vibration inducing factor.

Additionally, the longer focal length of the 12 inch scope makes precise pointing more critical. The use of focal reducers will mitigate this factor. It is the final actual focal length which is important.

Thus I think it is generally agreed that the 10 inch scope is a bit easier to use for imaging than the 12 inch because of the limitations of the mount.

Again, as good images can be had with the 12 inch as they can be with the 10 inch scope.

But great attention must be paid to the vibration problems with these scopes. I hope this sheds some historical and factual light on the topic.

---------------------------------

Subject: Which LX Scope Best for Imaging? --part 2 of 2   

From: Doc G

Michael McNeil wrote:
> Doc, did you use a accelerometer stuck to the OTA for this testing, as
> the ones I have seen are so sensitive they pick up the vibration and are
> sent to a op amp then to a chart recorder to match any further test
> where you hope you decreased vibration. Does this sound fair to you as a
> good test instrument? Mike

Essentially correct. I used a form of motion detector called a geophone. The accelerometer is sensitive to acceleration. (now that is a smart comment!!) The geophone is a magnetically suspended sensor that is sensitive to velocity. It goes to very low frequencies with great sensitivity. Down to 0.1 Hz easily.

I looked at the low frequency output with an oscilloscope and analyzed the signal with a spectrum analyzer. (Tektronix and Hewlett-Packard instruments) I measured in several directions. I was mainly interested in modes of oscillation that would affect the imaging, This is what I call nodding of the OTA. That is, angular motion of the OTA which causes the stars to move in the image plane. This can be vertical, horizontal or at any angle. The largest motion is generally parallel to the vertical direction of the RA axis.

The magnitude of the problem depends on many factors including things like the direction of pointing of the scope, the loading of the scope, the balance and too darn many things. I believe that is why imaging is so frustrating. One person will have good results and another poor results with what seem to be very similar setups.

Of course one of the main issues is to not excite the scope while imaging. Clearly you should not bump it or dance around it. Wind is one of the most terrible sources of excitation. I have become a strong believer in domed observatories for the protection that they afford from the wind. One can actually see waving your hand near the OTA body as a disturbance.

It is for the reason of wind excitation that I have been working on a domed building for my local astronomical society. My roll off building is very nice. But a domed building has certain excellent features for imaging in my opinion.

Subject: Best for Guiding: ST-4 or Pictor 216XE    

From: Greg Hartke <ghartkeclark.net> Date: Aug 2001

> -----Original Message-----
> From: Gordon Lupien
> Well... Does all this mean that it is better to get an ST-4 than a Pictor 216XE?
> What about the magnitude ratings, it seemed that the ST-4 had a much lower
> capability for dim stars...

I have both the 201XT and the STV. Alan Voetsch had both the ST-4 and the 201XT. Here are my experiences and a brief comment on Alan's:

I found that the 201XT worked quite well with a guidescope where the guide stars are well shaped and bright. It's very simple and reliable to use. I've also used the 201XT with the GEG. I developed techniques to make it really easy to use and it also worked just fine, with one caveat. The biggest difficulty with the GEG is finding a guide star bright enough to see with the 201XT with its uncooled chip. This can be a real pain. (At least, it was for me.)

With the STV, it's easier to find a guide star because it's much more sensitive. Surprisingly, the 201XT is actually easier for me to use than the STV but the STV is pretty straightforward, too.

I can say, "Oh, this one centroids to this fraction of a pixel and that one centroids to that fraction" and that's interesting but you still have to compare results under actual, realistic seeing conditions. (That's important because with better optics or astounding seeing the results might be different. I can't say. I can only report what I found.) My experience is that with my 10" f/6.3 LX200, imaging at the prime focus using the GEG the star images are identical (as nearly as I can tell) in 90 minute exposures under similar conditions with each guider.

The 201XT works fine but an autoguider with a cooled chip would be much better. I wish I could report my impressions from using the 208XT or the 216XT but I can't. I've never used either of them. I don't know how much more sensitive these guiders are. In addition, I know enough about centroiding algorithms to know that the increased dynamic range of the 16 bit A/D converter in the 216XT could yield better results, however I don't know if the firmware takes advantage of this. I haven't a clue how well any of the Pictors perform centroiding.

Alan Voetsch actually dumped his ST-4 because it's so cumbersome to use with his LX200 compared to the 201XT. Others have also told me privately that the ST-4 is fiddly. On the other hand, when used by one well versed in its complexities, it is reputedly an excellent guider. I don't doubt this in the slightest. SBIG products are well known for their excellence.

> Pixel size on the 216 is 10 microns square, and 14 X 16 microns on the ST-4.
> That also would point to better guiding via the 216 in the same optical
> setup, wouldn't it? Smaller pixels = more per fixed area = more information
> for the guiding algorithm for a given optical setup. Right?

Not entirely true. As I said, the ST-4 performs centroiding to approximately 1/5 of a pixel, meaning it determines the location of a star image to within approx. 3 microns at the focal plane. We don't know how well the 216XT does as Meade does not provide this information. It's reasonable to assume (and Meade has hinted) that the Pictors perform centroiding to subpixel resolution. It's of no use speculating to what degree this is true - only operational tests can tell if the resolution is adequate.

Subject: CCD Questions-- FWHM? & OAG w/Focal Reducer    

From: Mike Fuller <mfuller1satx.rr.com> Date: Sept 2001
<http://fullerastropix.web.com/>

Jerry wrote: I have a 10" LX200 equipped with the following components:

JMI NGF-S focuser
Meade off axis guider w/201 guider
Meade 416XTE

Question 1:
When using the Subframe tool in PictorView 7.1 to focus an image as the frame size is reduced a FWHM Graph is eventually displayed in the left viewing window. What does FWHM stand for? What is actually being measured? And finally what is the best way to use this graph while attempting to focus the image?

Answer 1:
FWHM stands for "Full-Width Half-Maximum" and represents the distance from the centroid (brightest central pixel of a stellar image) at which the brightness falls off by half, expressed as a diameter. It is measured in both axes (X and Y) in pixels, and gives a good indication of focus - not so much by it's actual amount, but by whether it is the smallest possible amount or not.

What is actually being measured is the number of pixels required to store the brightest portion of a star. Smallest numbers = tightest stellar image (and therefore best focus). Make sure to remember that what those "smallest values" will actually be will vary based on seeing, turbulence, etc. Assuming your scope is in thermal equilibrium and there is no other optical interference, the FWHM can be used to calculate your seeing - simply multiply the value by your known (or calculated) number of arcseconds per pixel.

The best way to use the values is to adjust focus until they are the smallest possible. You may pass through optimum focus multiple times before you are convinced that the values are as small as possible. From one night to the next, the "smallest value" may differ substantially, or may be very close. Time and experience will dictate to you what they should be.

With my scope, a 12" LX200 equipped with f/6.3 reducer, Taurus Tracker III, 616 CFW and 416XTE, in that order, I expect a binned image (I always focus binned for speed) to yield FWHM values between 1.0 and 1.35. This matches seeing between 2-3", normal for my area.

Question 2:
I recently purchased a Meade 3.3 focal reducer but have been unable to obtain focus with the off axis guider. It has been suggested that given the components I am using that the off axis guider will not work. What are my options to get the focal reducer into the optical path? One way or another I obviously need to be able to focus the 416 and autoguide? I suspect I am perhaps missing something obvious, perhaps not. Any suggestions?

Answer 2:
I have never been able to obtain focus with the f/3.3. Some individuals have, but with very limited accessories, or by placing the f/3.3 *after* the longest of the accessories. I don't know that this can be done with the off axis guider. I don't have a way to do it with my Taurus Tracker III.

Subject: Canon D60 Digital SLR for Astro Imaging    

From: Ron Burch, Date: Nov 2002

<Brianmec.co.nz> writes: followed with great interest a couple of weeks ago the thread on the Canon D60. I have the opportunity to buy a Nikon D100 "at the right price" which on paper look comparable to the D60. Does anyone have any experience in using this camera for Astro imaging, particularly DSOs?

I have been using a D100 for the past few weeks with a Celestron 8" SCT, a Meade ETX90, and a TeleVue 85. I find that it is quite good compared with my astrocameras Starlight Express MX916 and Cookbook Camera). While at this time of year I can readily do 45 - 60 minute exposures with the Starlight camera without much in the way of noticeable dark current subtraction, and 4- 6 minutes with the Cookbook, setting the ISO to 400 on the D100, I can readily go 4 - 5 minutes without any noticeable dark current when imaging a bright object like M42 (of course I do dark subtraction when using all of these cameras anyway!). I am looking for someone around here with a D60 to use for comparison since the impression I get from reading is the D60 with its CMOS technology has even lower dark current. Nikon D1's have much higher dark current than the D100 - inherent to the chip or some newer software manipulation (?). I also have a Nikon CP950 and CP4500 - the dark current for the 4500 is markedly lower than for the 950 so something positive is happening over time.

The D100 also has a noise suppression function that I have tried. For bright objects like M42, I have found that the "raw" image obtained has little dark current apparent after 10 -15 minute exposures BUT the image processing takes forever in the camera prior to download - up to FOUR minutes (the manual warns of this)! So I do separate dark subtractions rather than letting the camera do it. Of course, when using an uncooled imager like a D100 or any of the other non-cooled astrocameras where chip temperature can be controlled to a reasonable extent, darks need to be done adjacent to any image since the nighttime temperature changes a lot. Also, I have found and others have reported, if one does one image immediately after another, enough heat builds up in the camera body that each subsequent image is markedly degraded compared with the previous - the camera needs to "rest" for about 5 minutes (my casual observation but done only a few weeks ago when our nighttime temperatures were still in the upper 60's) between exposures.

There are several websites that evaluate the use of digital SLRs for astroimaging. One that I have found particularly interesting and useful is:
<http://www.panther-observatory.com/Review_CanonD60.htm> by Johannes Schedler. He has done a nice evaluation of the D60.

Subject: Digital Camera Hacks  

From: Andy Wallace <awallacejrsbcglobal.net> Date: June 2004

Seems the new high end digital cameras are like computers -- they can be hacked and the cheaper version of a more expensive model, like the Celeron chip, are simply derated versions of the more expensive chip, the Pentium.

Here's a Canon Rebel hack that makes it pretty close to a 10D? The camera can take pretty impressive astropics and the hacks would make it even better especially at a price of under $800 (which also like computers will probably be 1/2 that price in a year)
<http://www.bahneman.com/liem/photos/tricks/digital-rebel-tricks.php>

Subject: Suggested Powering Up/Down Sequence --part 1 of 3  

From: Mark de Regt <deregtearthlink.net> Date: Apr 2003

-----Original Message-----
> Alan Voetsch-- I have a 12" LX200. I have recently acquired a laptop with TheSky,
> CCDSoft, CCDOps, etc..., also an ST-7EI I want to use in place of the
> 208XT for autoguiding. I also got the cable from Scopetronix for the LX200.
>
> What I want to know is: should all this be hooked up before the scope
> is powered up? In what order should these things be powered up and/or
> down? Or does it even matter. And can everything be left hooked up or
> does it all need to be disconnected every night?

I always hook up the computer RS232 connection and the camera, and turn on both the camera and the computer, before I start up the LX200. I read that this is what one is supposed to do, but I don't remember where. I have been doing this for two years, and nothing has blown up yet, so I am not inclined to change it.

I shut down like this:

I disconnect the scope from TheSky, using the software; I close TheSky (you can turn off the LX200 first, but this complicates closing down TheSky). I turn off the temperature regulation on the camera. I turn off the LX200. When the camera has reached roughly ambient temperature, I disconnect the camera from CCDSoft (my camera control software), and shut down CCDSoft. Then I turn off the camera, then shut down the computer and the focuser.

--------------------------------------------------------

Subject: Suggested Powering Up/Down Sequence --part 2

From: Randy Marsden <jmarsdensan.rr.com>

I follow the same sequence as Mark and have had no difficulties. To power down, I shut down the scope first, then the other devices. The LX200 does not have good isolation for external voltage spikes. So, by powering up the other units first, you eliminate the potential to send a voltage spike to the scope when another device is powered up after the scope.

Hopefully the new GPS scopes have better isolation.

------------------------------------------------------------

Subject: Suggested Powering Up/Down Sequence --part 3 of 3   

From: Tim Long <Timlong-family.com>

In practice I don't think it really matters for an RS-232 connection (this is not true for ALL types of connection though). The RS-232 driver hardware should be robust enough to cope with pretty much anything. I always power up my scope first, to do any alignment/synch with an eyepiece. Then I hook up the camera and computer and power those up, camera first usually.

As far as leaving stuff connected, I think this depends on your local weather and the time of year. I find that I can happily leave stuff connected in the summer. I leave my scope out under a desert storm cover as long as the weather holds. If the weather is looking a bit dicey I take everything in. At the end of last summer I got a bit lazy about taking things in (and the weather in UK is notoriously unpredictable). I ended up getting some corrosion problems on some of my connectors. So now I try to discipline myself to take all the cables in at the end of each session (but I still leave the scope out if the weather is OK). The legs on my tripod are getting a bit rusty because the cover doesn't go all the way to the bottom, but I plan to rub them down and paint them with Hammerite once they get too bad. Long term I plan to build an observatory and put the scope on a pier, so the tripod will then be redundant anyway.

Webcam & Video Camera Topics

Subject: Meade's LPI as an Autoguider?   

From: Todd Brower <toddtoddbrower.com> Date: Dec 2003

-----Original Message-----
From: Jesse Ruder <jhruderearthlink.net>
I would like to know if any of you might have some direct experience using the LPI as an autoguider. The internet is filling up fast with info about the LPI's interesting, though modest, imaging capabilities, but --so far-- nothing about its autoguiding performance.

I have one and after surviving the challenging installation process, I am intrigued by the simplicity of the software Meade provided for it. I should add that just in case any of you are thinking about getting one, the software installation was reminiscent of a minefield I crossed a long time ago. It took many frustrating hours discovering the booby traps that Meade's installation instructions overlooked including in their documentation.
-----End of Original Message-----

I was able to get the LPI to autoguide my 8" LX200GPS. It plugs into one of the serial ports, so it will only autoguide a meade mount. The trick to get it to work is that you must be set to guide rate on the AutoStar controller and you must set the guide rate in the menus to 40% sidereal or less. I also had to set the guide correction in the LPI software to 0.2 instead of 0.5. With these changes I was able to calibrate and guide good enough for photos. Without these settings your are doomed to have the LPI overcorrect and the stars will run in circles.

Subject: Experiences in Installing LPI Software   

From: Jesse Ruder <jhruderearthlink.net> Date: Dec 2003

I took notes as best as I could during the experience, but for reasons to follow they don't represent a foolproof recipe for installation success. Here goes:

The computer in question is a 5-year old Dell Inspiron 3500 (laptop) with a Pentium II, 300 Megahertz CPU, 256 Megs of Ram and a 6.1 Gig hard drive, with about 3.5 Gigs still open. I am running Windows 2000 Professional on it. The various references from Meade on what the LPI system requirements were, conflicted a little--one from another. After many hours of ducking and dodging problems, my laptop turned out to be enough to run the LPI software. I wish I could tell you what all of the problems were, but alas, My memory on some of the matter is a little fuzzy. I will do my best.

#1. LPI needs an OS of Windows 98 SE or better.

#2. A Microsoft program called "DIRECTX" must be downloaded and installed first.

#3. Another software item from Microsoft which is included on the Meade installation CD must be loaded and installed. It is called ".NET FRAMEWORK 1.1." This is where my first big problem came in. dotNET... would not install. I think I got an error message about the "Installation Wizard." After going back to the first step several times with the same failure. I called Meade a few times along the way. They told me that many LPI users have installed the software with no problems at all. They didn't add that there must be something wrong with me, but I heard it anyway. The Meade web site troubleshooting page suggested that dot NET... could also be downloaded from the MEADE website. The Meade site told me where on the Microsoft site I could find it. I followed the instructions and tried to download dotNET... At some point the download failed, over and over.

At this point I called Microsoft. The people I spoke to admitted that They didn't know how to help me but eventually put me in touch with a fellow who could. His name was Dupak. He works for Microsoft, but lives in India. I had to struggle to understand his accented English, but about five to six hours later, managed to get dotNET... installed by following a procedure different from the ones provided by Meade. Dupak saved the day for me. DotNET... was downloaded from a different page on the Microsoft website and there were a few other steps I am not certain about. The most important were the entry of two items at the command prompt level as follows:

msexec /unregister **
msexec /regserver **

*I must warn here that in a later attempt to recover from an disk failure, I tried to repeat this step and it failed, so I may not have taken notes as well as I might have--sorry.

After more hours than I counted, it finally worked and my shiny new LPI performed like a charm in my living room. I used a tiny LED about 35 feet away as a target. I plan to try it outside purely as an autoguider when the weather is once more fit for arthritic toes. But the thrilling tale does not end there.

After getting everything working, my hard disk died, not to be brought back to life. While I wait for a new hard disk for the laptop I tried to install the LPI software on my desktop computer. It is a Dell Dimension 8100, Pentium IV, 1.4 Gigahertz machine with about 3/4 Gig of ram and a 40 Gig hard drive. Like my deceased laptop, it too runs Windows 2000P. NONE of the problems mentioned before occurred. The installation was performed completely from the Meade supplied CD. When I tried to run the program. It reported that the LPI driver could not be found. During the installation the system had reported at one point that the driver had been successfully installed. I ignored that and went through the process again. After this trial, I tried again to run the program so as to play with the LPI camera and lo and behold. It all worked perfectly just as it had eventually done on my now inoperable laptop.

Some additional comments are in order:
I must emphasize that my installation difficulties related only to my older less well-equiped laptop. Except for the minor driver snag the installation on my much more muscular and modern desktop went smoothly.

Also, Todd Brower gave me some results from his LPI experience. He reports that two adjustments were required to get the LPI to track properly. First is to set the Autostar guide rate to 40% of sidereal or less. Secondly, the LPI program has a default guide correction of 0.5 which must be dropped to 0.2. Without these changes, Todd added that the LPI over corrected and made the stars run in circles.

Subject: Video Camera Advice --part 1 of 6   

From: Bruce Gillespie <brucepcb.co.za> Date: Mar 2003

>I'm considering the purchase of one of the following : Astrovid
>StellaCam EX, OR SAC8 OR MINTRON, 12V1E-EX.
>Any experience and/or words of wisdom on either or all of these three?

I got the StellaCam EX - and am still on the learning curve, nothing decent to show for the expense so far. The control box is a bit tedious, though I see they now offer a Serial I/F so one can control it from a PC (I can see another upgrade coming on ...) It has a lot more modes and controllability than the others. I must say I think I am going to need a remote controlled fine focus since its very sensitive to focus and to keep moving between the scope and the PC is a very tricky.

I have also got the Video Capture Essentials PCMCIA Video Capture device - and that seems to work well. Nice software. I did some market research, decided not to go with any of those USB devices (Belkin etc.), this one seemed more professional. I got all this from John E Cordiale at Astrovid, they handled things well, no problems (though didn't tell me about forthcoming RS232 i/f on Control Box)

The April Sky &Telescope has a review of 'low cost' video cameras, so check that out as well.

-----------------------------------------------------------

Subject: Video Camera Advice --part 2

From: Edward Registrato <amnet_edqwest.net>

The Astrovid 2000 is a good black & white camera. I own one and use it a great deal. I have had high school students (age 15-18) that used it the first night and it works right out of the box every time.

There are limits, however. It will not do deep sky images. It is (in my opinion) only for Venus, Jupiter, Saturn, Solar, and Lunar type images. We also have it connected to a 35-80mm lens and have used it for meteor showers, wide area views and daytime camera.

We have connected it to a HELIOS-1, a 76mm Televue and into the LX200 10" classic. The output first goes into a super S video machine and then that goes into a video capture card in our computer. We can frame grab some good images that way. I can send you a few if you want to see them. We have taped eclipses, moon craters, and solar activity.

Don't expect CCD quality images that you see in Astronomy or Sky & Telescope. You wont get them that good when you try to print. The data is just not there. The images are fine for viewing at high school levels. Photo Shop helps but can not improve the amount of data.

The camera also works for showing an image to large groups on a monitor. I have used it with wheel chair bound individuals and older nursing home residents that can not look through the scope. Looking at Jupiter and the moons is probably the favorite view for these groups.

As for customer service... I rate it very good. They have not responded to my last email for help but that has not been consistent with the response I have gotten in the past. I have no experience with the other cameras they have.

-----------------------------------------------------------

Subject: Video Camera Advice --part 3

From: Tony Floyde <tony.floydelineone.net>

I have been looking at the Mintron cameras myself and the camera they produce that has frame integration and on screen display which is called the Sirius in the UK and cost 275 and for the life of me I can't see the difference between that and the Astrovid Stellacam EX except the badging and a 1.25" tube so I believe that the Stellacam is the Mintron, in the UK the price difference is 275 Mintron 645 Stellacam what would you do. A friend of mine has the Stellacam bought when it first came out before I found out about the Mintron really rates it he lives in a light polluted city and can image things he cant see with his eyes. The Mintron is used by the military to monitor tunnels it saves on attaching image intensifiers to the cameras. Mintron also do a colour version with a 1/2" CCD that is the same as the B & W only it only goes down to 0.0001 Lux on integration as opposed to the B & W which goes down to 0.00001 Lux on integration. For what it's worth save some money and get the Mintron over here in the UK you can get the B & W and the Colour version Mintron's for the cost of the Stellacam.

-----------------------------------------------------------

Subject: Video Camera Advice --part 4

From: Bruce Gillespie <Brucepcb.co.za>

> for the life of me I can't see the difference between that and the
> Astrovid Stellacam EX except the badging and a 1.25" tube

Perhaps you are right and the camera tube is the same, but the Stellacam EX has a custom made control box to switch modes, gain control, frame accumulation modes etc etc - surely that involves some significant electronics and processing power in the box beyond the camera? If you look at most of the others they have automatic gain control which can be quite annoying. That's why I went for the "StellaCam", besides I like lots of settings to tweak.

However if use is recording occultations, perhaps the simpler models or even an adapted Webcam or Video camera will do. See Massey, Dobbins Douglas "Observer's Guide to Video Astronomy" (Sky Publishing, 2000) for comprehensive background on this.

-----------------------------------------------------------

Subject: Video Camera Advice --part 5  

From: Russell Croman <russellcroman.org>

Webcams are definitely the cheapest way I know of to get into digital astrophotography, assuming you already have a computer to run the camera, and of course a telescope.

> Is your picture the best 500 frames out of 1800 frames?

Yes. I used a free program called RegiStax to automatically pick the sharpest 500 frames.

> Did you just run the web cam as a true "web cam" and stream the
> images or did you take 1800 stills?

I used another free piece of software called K3CCD Tools to stream an AVI file to disk. It was running at 15 frames per second for two minutes. Generates about 800MB worth of data.

That's the nice thing about using web cams for planets... you can get enough data in a short enough period of time that planet rotation doesn't smear things out.

> Where did you get this camera? Locally, or mail-order/web-order?

I had heard (on the "QCUIAG" yahoo group) that the Philips ToUCam Pro is one of the better webcams. Apparently they are in low supply (like maybe they aren't being made anymore). I got mine from <http://www.pocketscope.com>. I think they still have some.

> Did the post processing add a lot to the image? If you just took 500
> frames and stacked them, how good does the picture look?

The raw image is quite a bit blurrier than the processed one. Processing algorithms have gotten very sophisticated, and available to amateurs, of late.

> How did you mount this to you telescope?

I got a 1.25" adapter from an Australian guy named Steve Mogg:  <http://webcaddy.com.au/astro/adapter.htm>
It replaces the lens on the webcam and slides right into an eyepiece holder.

-----------------------------------------------------------------------

Subject: Video Camera Advice --part 6 of 6    

From: Bob Thompson <bobnstarprovide.net>

I read about an inexpensive B/W video camera from SuperCircuits in Austin, Texas <http://www.supercircuits.com/>
that has a sensitivity of 0.04 Lux and operates on 12 volts. It is only $89.95 so I ordered one. It is the model PC-23C and includes a microphone and audio circuit built-in. The CCD has 510 by 492 pixels and produces 460 TV lines of resolution. On my first night out with my 10" f/6.3 LX200, I watched a 10th magnitude star as it was occulted by the 1st quarter moon. I could see the dark limb of the moon as it closed in on the star. I could just see several 12th magnitude stars above the background noise (or skyglow?) level with the moon in the sky. And this is in the city with severe light pollution! I have not had a clear moonless night to see if I can do any better. I could not see individual stars in M13 or M3 but will try again on the next clear night. Give it a try, I think you'll like it.

Update (Oct 2002): new SuperCircuits PC164 that has even lower lux, in a smaller package.

Subject: On-line WebCam Resources List   

QCUIAG Discussion Group:
   <http://www.qcuiag.co.uk/> Homepage for QCUIAG
   <http://groups.yahoo.com/group/QCUIAG/>

Camera-Modification Websites:
   <http://home.socal.rr.com/hotweb/vesta/>
   <http://mypage.bluewin.ch/bm98/>
   <http://www.unm.edu/~keithw/astroPhotography/cameras.html>
         Author of Keith's Image Stacker software (Mac).
   <http://astro.ai-software.com/> Huge list of webcam mod & software sites

Commercially-Modified Webcams Websites:
   SAC Imaging: <http://www.sac-imaging.com/main.html>
   Perseu: <http://www.perseu.pt/> Portuguese
                <http://www.perseu.pt/index.html?lang=en-us> English
   Comparison of models: <http://homepage.ntlworld.com/molyned/web-cameras.htm>

WebCam as a Guider:
   <http://users.ameritech.net/mniemi000/auto.html>

Image-Acquisition Software Websites:
   Astroart <http://www.msb-astroart.com/>
   Astro-Snap <http://astrosnap.free.fr/> French
                     <http://astrosnap.free.fr/index_uk.html> English
   K3CCDTools <http://www.pk3.org/Astro/> select "My Software"

Image-Processing Software Websites:
   RegiStax <http://aberrator.astronomy.net/registax/>
   Iris <http://www.astrosurf.com/buil/us/iris/iris.htm>

Subject: WebCam Advice --part 1 of 5  

From: Clifford Peterson <CPETERSONweber.edu> Date: Sep 2003

I have been seeing stacked webcam photos of bright objects that actually look very good. This has sparked my interest and am thinking of getting a device to experiment with.

MAPUG already has members that are working with these devices and know much about the subject so I would be interested in any suggestions for a device selling for about $150 or less. I have seen articles where a Philips USB ToUCam Pro was used but it doesn't seem like there are many sold in the USA. Is this a good cam or should I be looking in other directions?

-----------------------------------------------------

Subject: WebCam Advice --part 2

From: Todd Brower <toddtoddbrower.com>

I've been having some pretty good luck with the QC 4000, I think the quality is pretty much the same as the ToUCam. I've done this for a QC 3000 but never really put time in for much testing/usage. I did get a pretty good M13. I'm going to set up a water cooler for it soon and restart testing but for now my QC 4000 is good for the planets.

The QC 4000 software comes with an interesting feature that I have tested but haven't had much luck with it as of yet. They call it "face tracking" and it seems to be somewhat of a software image stabilizer. You zoom into the image and turn on face tracking and it is supposed to keep the imaged centered. The time I tried to use it on mars, it kept changing the zoom level in and out but that may have been because it was moving too much due to atmosphere. Also, I think you may have to use the software that came with it to capture the AVI. I've been using K3cddtools to capture and perhaps it didn't know how to deal with that feature. It's an endless adventure.

You will want the IR filter if you use the ToUCam. You'll have to put your order in pretty quick for the adaptors unless you want to go the route of making your own from a 35mm film holder.

-----------------------------------------------------

Subject: Web Cam Advice --part 3  

From: Roger Hamlett <ttelmahntlworld.com>

The 'point' about the ToUCam, is 'multifold'. Perhaps 90% of the cheaper webcams, use CMOS sensors, which are not designed with any thought of 'low light' usage. Unfortunately, their sensors perform relatively poorly for astronomy. The ToUCam Pro, uses probably the best webcam sensor, in the form of a small Sony CCD. The internal amplifier, has about the highest gain of any webcam (also good for low light), and the drive chip used is one for which there is a 'known' relatively simple modification to give long exposures. There are even modifications to use the basic control board, and operate a more expensive larger CCD!.

It is generally surprising how 'good' many webcams can be, but for really deep sky work, the modifications rise to the point of being as complex as building a new 'cookbook style' camera (long exposure mod, new CCD, Peltier cooling, etc. etc..). However the key thing is that the ToUCam can take some quite good images 'out of the box', and with relatively small modifications can match the performance of some of the earliest 'proper' CCD cameras, for a very small price indeed. Hence it is the 'favoured' unit. There is also a Quickcam model, that is similar, but with slightly lower amplifier gain, that works nearly as well.

Unfortunately, for some reason, Philips elected not to offer this model in the US, but as Ron points out, one of the astronomical dealers has 'stepped into the breech' in this regard.

-----------------------------------------------------

Subject: Web Cam Advice --part 4

From: John Mahony <jmmahonyhotmail.com>

Actually, there are two: Scopetronix and Astrovid. Both sell the camera and adapter for $150. You can save some money by ordering separately: The camera is available from <http://www.pocketscope.com> for $92 +~$8 shipping, the adapter is $20 +~$4 shipping from <http://www.webcaddy.com.au>. Fortunately, Pocketscope is a small company that sells a little microscope kit, not telescopes, so they haven't jacked up the price for Mars Mania.

My best Mars image is at <http://geocities.com/jmmahony/mars0725.jpg> if you want to see what a ToUCam can do.

-----------------------------------------------------

Subject: Web Cam Advice --part 5 of 5    

From: Ron Mollise <RMOLLISEaol.com>

Let me take this excellent information one step further. On the Moon and planets, the ToUCam and similar webcams (like the Quckcam Pro 4000) will equal or BEAT--undeline that, BEAT--the most expensive integrating cameras on the market. No doubt about it.

They are not quite as well-suited for the deep sky, but people are doing remarkable work with them anyway. For those like me who lack the time and skill to do the mods themselves, SAC <http://www.sac-imaging.com/> offers several cameras that are professionally modified up to and including long exposure, cooling, and decent housings. Even if, like me, your main interest is the Solar System, a long exposure camera offers some nice capabilities...like being able to capture planetary satellites and asteroids.

Subject: SAC WebCam For Starting CCD Imaging --part 1 of 3    

From: Tom Skinner <dateachva.prestige.net> Date: Oct 2002

Doug Kranz wrote:
> Any advice re lower end CCD cameras with an LX200 10"?

For a cheap webcam, take should take a look at the SAC camera: <http://www.sac-imaging.com/main.html>

The SAC camera are modified webcams, but professionally done and, in my humble opinion, a pretty good place for a beginner to start. You won't spend a lot of money, and if you decide to step up later, the SAC would make a good autoguider.

There are tons of free software packages out there for camera control, image acquisition and image processing. See the links below.

---------------------------------------------------

Subject: SAC WebCam For Starting CCD Imaging --part 2     

From: Randy Marsden <jmarsdensan.rr.com>

This camera is a commercialized version of a Philips webcam with modifications for long exposure and removal of on-chip amplifier glow. A lot of information about using this type of camera for astrophotography can be found in the QCUIAG Yahoo group. The modifications were developed by a member of that group. The Yahoo group address is http://groups.yahoo.com/group/QCUIAG// . Some of the members have recently been taking some nice deep space shots. Without any modifications, the Philips and some other CCD-based webcams can be used to take very good lunar and planetary astrophotos. The same group also has a wealth of information about that application.

Another recent development has been the use of webcams and some of the image processing software to obtain the data to quantify and plot PEC, RA, and dec drift to help improve polar alignment. It has been cloudy here or I would have done this already. When I do, I will post a message here with a link to the data which I will post on a web site. The readily available webcams cost under $100 and the software is free - links to the various programs are on the QCUIAG website. So in about 15 minutes, you could obtain an accurate graph of alignment and PEC error and perhaps even details deeper into the gear train. The basic procedure is described in a message
  <http://groups.yahoo.com/group/QCUIAG//message/28955?threaded=1>

and a sample graph is at:
  <http://home.online.no/~arnholm/astro/software/rxpec/1800frames_altair.gif>

----------------------------------

Subject: SAC WebCam For Starting CCD Imaging --part 3 of 3    

From: Ted Wilbur

I've had a SAC 7 for about 8 months. It is capable of taking some nice shots but the chip and pixel sizes are very small. The SAC 7 has a postage stamp field of view of 3.7x4.9 arcmin on the LX200 10" F10. The image scale is just 0.46 arcsec per pixel, it can't be binned, and isn't particularly sensitive IMO. It works ok on small objects like planetary nebula.

I use the SAC 7 occasionally on my LX200, but have had the best results using it on my old ETX70 which has a very large field of view. Some of the images I've taken with it are posted on Weasner's Mighty ETX site. (Goto homepage for link)

The SAC 7 isn't a bad starter camera, particularly now with the planets coming back around. Just be aware that the FOV is super small, even if you use a focal reducer.

Editor's Note: also checkout PolarisUSA Video's Day/Night CCTV Cam: <http://www.polarisusa.com>

Subject: Webcam Guider? --part 1 of 4  

From: Doug George <dgcyanogen.com> Date: Sep 2003

Bostjan wrote:
> The recent discussion on Webcams was really interesting. I was wondering
> if anybody has ever tried to use one of them as an autoguider? Is there
> any software available that is able to do that?

Some of our MaxIm DL/CCD customers use webcams for autoguiding. Some webcams are more sensitive than others, though.

We also just released a "new and improved" video/webcam plug-in driver, available from our driver downloads page.
<http://www.cyanogen.com>

---------------------------------------------------------

Subject: WebCam Guider? --part 2

From: Jerry Horne <jerry_hornesbcglobal.net>

Try: <http://astro.ai-software.com/>
This lists several webcam guider projects and related software.

--------------------------------------------------------

Subject: WebCam Guider? --part 3

From: John Mahony <jmmahonyhotmail.com>

Astrosnap <http://astrosnap.free.fr/index_uk.html> webcam freeware will handle just about everything that can be done with a webcam, including autofocus if you have an LX200 with the 1206 focuser.

--------------------------------------------------------

Subject: WebCam Guider? --part 4 of 4  

From: Gene Chimahusky <lynol1000yahoo.com>

Bar none the best guider SW for webcams is a dos based program that only works with the old Connectix Quickcam B&W for pc's. If interested check out:

   <http://users.ameritech.net/mniemi000/auto.html>

The B&W Quickcam is not very plentiful but do come up on eBay. It is the only cam that only requires snipping one wire to enable long exposures (without cooling of course).

The guider.exe SW is so feature rich, and freeware, that it can provide complete control over the lx200. The other SW works, but none hold a candle to guider.

Subject: WebCam Purchase Advise  

From: Gene Chimahusky <lynol1000yahoo.com> Date: Sep 2003

To date the most sensitive stock cam is the Philips ToUCam based on the icx098bq CCD. Older Philips Vesta's used the icx098ak, some newer ones use the bq. Logitechs and others are also based upon the bq but the ToUCam still win for sensitivity because of the support circuitry and amplifiers. The biggest issue with webcams is the max exposure length of an unmodified camera, which comes in around 1/25sec or 1/5sec with a few tricks. There are more sensitive surveillance cams but the hookup there is analog video. People mod the cam to use the icx098bl (B&W version of same chip) which shows greater sensitivity.

Check here:
  <http://homepage.ntlworld.com/molyned/web-cameras.htm> for a webcam list and sensors used.

Do use plan to guide the main scope via piggyback or off-axis or used the main scope as the guider for more wide field shots? Obviously the aperture of the guide scope will have a large effect on the dimmest star you can guide with, especially with an un-modded webcam.

I have a modded ToUCam, a stock Vesta and a Quickcam B&W. Again, the QuickCam with a wire snip mod for long exposure up to a second or two without cooling sure makes guide star selection easier and guider.exe beats the rest of them for SW.

Subject: WebCam Discussion Group --part 1 of 2  

From: Doc G, Date: Sep 2003

There is a very large webcam group. It is a Yahoo group and will tell you more than you wanted to know about web cams. Ask the question there. It is called QCUIAG. Find it at:
<http://dir.groups.yahoo.com/dir/Science/Astronomy/Astrophotography?show_groups=1>

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Subject: WebCam Discussion Group --part 2 of 2

From: John Mahony <jmmahonyhotmail.com> Date: Sep 2003

The QCUIAG home page is <http://www.qcuiag.co.uk/>
The QCUIAG yahoo group is at <http://groups.yahoo.com/group/QCUIAG/>

For autoguiding, you can use Star Track (purely autoguiding software), Astrosnap (autoguiding and advanced image capture program), Iris (just about everything), and several others. Most of the software is freeware. One of the nice things about webcams is that their development for astro-imaging has been developed almost entirely by amateurs, so there's tons of great freeware for them. See also K3CCDtools and Registax.

Subject: IR Filter On WebCams --part 1 of 2  

From: Russell Croman <russellcroman.org> Date: Aug 2003

--- Robert wrote:
> I have a webcam and have been reading a lot about IR filters.
> Can someone tell me what it does and is it a must have filter.

Robert, there are a couple of reasons to use them. One is atmospheric dispersion. At the high magnifications used for planetary work, the dispersion of the different wavelengths by refraction in the atmosphere causes a significant blurring of the image, and also colored edges on the planet. This gets worse as the altitude of the object decreases.

Adding an IR blocker removes a big section of wavelengths, reducing this effect. Many folks like to use a UV/IR blocker to handle both ends of the spectrum this way.

The other reason is color balance. The IR signal shows up in the red channel, and sometimes also leaks into the blue and/or green channels, depending on the color filters used in the webcam. This can really mess up color balance, giving an unnatural look that is hard to compensate for in processing. See my website for more: <http://www.rc-astro.com/>

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Subject: IR Filter On Web Cams --part 2 of 2  

From: Peter Campbell <peter.campbelltwc.state.tx.us>

Web cam CCDs are very sensitive in the IR, but the R, G, and B filters built into the CCDs do not filter out IR. All CCD cameras come with a built in IR filter to fix this. Problem is that the IR filter in the ToUCam is in the lens, not on the CCD chip, so when you remove the web cam lens you remove the IR filter. The QuickCam has the IR filter on the CCD holder, and it does not get removed when you remove the lens.

Now, what is the problem with detecting IR? An IR source will look white to a web cam with no IR filter because the IR passes through all the colored filters equally well. The software thinks that all the light detected through the blue filter is blue even though some of it may be IR. Allowing IR to get through will cause images to looked washed out due to the extra "white" signal. The color balance can be really bad too, if the camera has been balanced with an IR filter. Also, most lenses are not well corrected in IR and you will get really bad chromatic aberration if you don't filter it out. Atmospheric dispersion is also an issue at low altitudes. However, if accurate color is not an issue and you are not imaging too close to the horizon and there are only reflecting surfaces involved, you don't need an IR filter.

Subject: WebCam Acquisition Technique with AstroSnap-Pro  

From: Sylvain Weiller <sweillerfree.fr> Date: Mar 2004

I have developed this acquisition technique usable with webcams, video camera and digital cameras to use less space on disk (50x or more), accelerate registration, enable slower processors speeds and less RAM ... Archiving them!

See: <http://sweiller.free.fr/> and click on AstroSnap-Pro link and follow.

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