LX200 Astrophotography--Page 3

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Lens/Camera/Imager Adapters      Top

From: Doc G

Attaching Standard Camera Lenses to CCD Imagers

This note describes the problems which arise when trying to attach standard camera lenses to CCD imagers, their solution and other ideas for convenient attachment of optics and receptors in the dark. (sometimes the cold, cold dark)

There are two problems that must be solved. One is obtaining a suitable camera flange to for the lens mount. Modern lenses generally are of bayonet mount type and thus require an adapter plate which mates to the lens. This plate is like the flange on the camera. Additionally, there must generally be a mechanism that allows the lens to be stopped down. If the lens is to be used at full aperture, the latter is not required.

The second problem is to adapt the camera flange to a T-thread adapter and still keep the total thickness of the adapter small enough so that infinity focus of the lens will allow it to focus on the CCD chip.

A knowledge of the camera flange to film (focus) plane distance is necessary and a way to make a male T-thread on the back of the adapter are required. This is because CCD imagers generally have on their front surface a female T-thread. Unfortunately, the imaging chip in the CCD imager is some distance behind the front surface of the T-thread. In the 416XT this distance is 15.5 mm. In the STs it is 23 mm. In the 216XT it is only about 11 mm since the 216XT has no shutter mechanism. This means that the adapter can only be a thickness equal to the camera flange to film distance minus that for the CCD imager.

I have made a number of adapters for Canon lenses. These are among the most difficult since the Canon flange to film distance is only 42.1 mm. This is among the shortest of all modern 35 mm SLR cameras. (See list attached at the end of this note.) It is so short in fact that even a Nikon to Canon adapter can be and has been made. It is only 4.4 mm thick and has both the male Canon bayonet and the female Nikon bayonet within its structure. This is a real tour de force in adapter design. I still have one on a Nikon 500 mm f 5.0 mirror lens.

Most adapters for lenses for other cameras are not quite as difficult as those for the Canon because the flange to film plane distances are larger. The easiest lens to adapt is a T-mount lens. The standard T-mount to film plane distance is 55 mm. Thus all that is required is a straight through female T to Male T tube. Unfortunately T-thread lenses are now quite rare and obsolete. There were never many really high quality lenses of this type made that I know of. They were mostly cheap. But you might want to search out camera stores and be lucky enough to find one of the few good ones made. (Do not underestimate the quality of the lens required for CCD imagers. A 10 minor pixel CCD can resolve 100 lines per mm. So you want a lens significantly better than this resolution and longer focus lenses that do this well even on axis are not all that common until the last 15 years or so.

Usually, it is desired to place a good quality 35 mm lens on the CCD imager. I will describe below a method to do this which produces, in my opinion, a professional quality Adapter.

It is so difficult and time consuming to produce the bayonet mount for any good lens, such as Canon or Nikon, that this part, the female bayonet must be purchased. The preferable product to purchase is an adapter which has a quality bayonet mount and the mechanism for stopping down the lens manually. The rear of the adapter would ideally have a T-thread and the problem would be solved. Unfortunately, such an adapter does not exist to the best of my knowledge. At lease I have not been able to find one. The reason of course is that all camera flange to film distances are much less than the T-thread distance of 55 mm. Of course, the 55 mm was chosen so that T-thread lenses could be adapted to any SLR.

However, it is quite possible to obtain adapters for specific lenses which adapt the lens to a standard C mount which is used on many movie and video cameras. Thus this is the adapter type to purchase. Now if the adapter is made right, the C thread will be on a removable element. Such is the case for an adapter made by NPCM and supplied to almost any good camera dealer. They will most likely have to order it for you. This adapter has a removable C thread piece on the back leaving a flanged hole 38.2 mm in diameter and 3.9 mm deep with three set screws in its rim. Into this flanged hole an turned piece can be attached which carries the male T-thread required to mate with the CCD imager female thread.

This piece needs to have a thread which is 42 mm diameter by 0.75 mm and 5.0 mm thick. (the T-thread) And then a step down to 38.2 mm for a distance of 3.8 mm. This small stepped (donut shaped), threaded ring is inserted in the flanged hole and tightened with the three set screws. And there you have it. A perfect adapter for the selected bayonet lens to T-thread. This small part can be made of brass which is very easy to machine. I believe the above described adapter is designed and made in about the easiest way possible. Anyone with a small lathe can make it easily. I have made several for myself and friends. I use another adapter with the original C thread to attach Canon lenses to my video cameras.

One can also make the bayonet camera mount the basis for several adapters for CCD, video or standard cameras to the telescope by using the Schmidt to T-thread tube with a standard T-thread to camera ring. Then any of several receptors, camera, CCD, video camera or other can be quickly bayoneted to the telescope. Of course all the receptors should be made parfocal.

For example, I have made up several parfocal eyepieces by mounting an eyepiece in an appropriate length tube and adding to the front a camera bayonet flange. Then one can focus visually, bayonet off the eyepiece and bayonet on the receptor. This is especially convenient with the Canon bayonet mount since it is of the breach mount type. That is, it has a bayonet flange which is tightened with a rotating ring similar to the breach of a cannon. But other bayonet mounts are also very good.

I made most of the attachments described when I got tired of screwing and unscrewing Schmidt style rings.

  Flange to Film Plane Distances
 Leica (screw)28.8 mm   Leica (M bayonet)27.8 mm 
 Canon (screw)28.8 mm   Canon (FD and earlier)42.1 mm 
Nikon  46.5 mm Minolta 43.5 mm 
Pentax K 45.5 mm  Exacta 44.7 mm 
Alpa Bayonet 37.8 mm  Contarex 46.0 mm 
Contax RTS 45.5 mm  Ikarex BM 44.7 mm 
Konica Autoreflex 40.5 mm  Miranda 31.5 mm 

(41.5 mm?) 


Praktica/Pentax *

45.5 mm 

Olympus OM 46.0 mm   Ricoh Bayonet 45.5 mm 
Petri Bayonet 45.5 mm  Topcon DM44.7 mm 
Rollei 35 44.7 mm  Yashika FR, FX  45.5 mm
Voigtlander 44.7 mm    
* also Alpa 2000 Si, Argus, Chinon, Contax D and S, Cosina, Edixa, Fujica, GAF, Ikarex TM, Mamiya?sekor, Petri, Pentacon, Ricoh, Spiraflex, Vivitar, and Yashica SLRs with M42 Universal mount. 

More info is available at my website A new browser window should open over this page.


Subject: Adapter to Attach Flip-Mirror?    Top

From: John Mahony <jmmahonya_thotmail.com> Date: Feb 2004

From: Dave Lillis
>A question for all those out there who have the Meade 2" flip mirror.
>I have a Canon EOS camera and I know I need the T-ring that fits this
>camera (didn't order it yet), but what I'm trying to figure out is how
>does this T-ring attach to the flip mirror.
>Does it screw into one of the adapters that come with the flip mirror or
>do I need to get another adapter?

The T-ring allows your camera to attach to T-threaded camera adapters. The flip mirror comes with three adapters for the back, and two of these end in T-threads. The short one is for film cameras, the long one is for CCD. I don't if your Canon EOS is film or digital. If it's digital, but designed to work with the same lenses as the film cameras, you'll probably use the short adapter. At any rate, it's only a matter of getting the optical path length right so that the EP will focus, and the EP holder has a fair amount of focus-adjustment range. So a worst-case scenario is that you _might_ need an extension tube (either for the EP, or a T-threaded extension, for the camera), but get just the T-ring first, and see how it works out. If you can't reach focus in the EP, you can try a different EP, but it's best to use a crosshair EP, because that will force your eye to focus on the crosshairs, thus fixing your eye focus, so that the camera focus will be consistent.


Subject: Opposite of a T Adapter --part 1 of 7    Top

From: Gary White <white512a_taustin.rr.com>

-----Original Message-----
From: Rod Cook
I have several Pentax camera lens I would like to mount on my CCD
camera. I need effectively the opposite of a T adapter. Are these made?

They do, but the trick is to find one that has the right lens to CCD spacing so as to achieve focus with the lens set to infinity. From my experience this may not be possible...

I got one from the guy that sells the Stilleto focuser, for my EOS lenses, but was never happy with it. He sent me another one that was a bit better and then went into a long spiel about how it was not possible to achieve this after he had advertised a perfect focus at infinity with my EOS lenses with his adapter. Can I use it and bring the lens into prime focus? Yes, but with all of the issues of focusing you have with a normal CCD. So that is one thing I'd look for.

Anyway, I use mine to test CCD operations after I have been away from the CCD equipment for awhile. I can set it up in house w/o scope and refresh myself on camera and s/w ops so I don't waste an observing session. I've also used it to teach myself how to setup the 201 XT by focusing on a light about 400 feet away (outside) with just the EOS lens. It is a great time saver over shelping out the telescope...

Another solution might be to find an old junk Pentax camera and use it to create a mount. I'm assuming your CCD has a female T thread? This might require some metal turning to get the lens mount off the Pentax to fit onto a tube that has a male T thread to then fit into the CCD.


Subject: Opposite of a T Adapter --part 2

From: Joe Shuster <jshuster42a_tcomcast.net>

I think what you're asking for is a female M42 to male T adapter. Until 24 hours ago, I didn't think they existed, but someone answered a question I had with a link to:
<http://www.alpineastro.com/eyepiece_adapters/eyepiece_adapters.htm#Telescop e%20Adapters>

and viola! Check the adapter labelled "Russian...". That should do the trick for the threading.

However, I hope you know you need to control the distance from the rear of the lens to the CCD surface. For each lens system, this is fixed. For the Pentax system, it's 45.5mm IIRC.


Subject: Opposite of a T Adapter --part 3    Top

From: John Mahony <jmmahonya_thotmail.com>

>From: Joe Shuster:
>I think what you're asking for is a female M42 to male T adapter.

M42 (if it's 1mm pitch) fits the old Pentax thread mount lenses, but modern Pentax lenses and most other brands use a bayonet mount.

>However, I hope you know you need to control the distance from the rear of
>the lens to the CCD surface. For each lens system, this is fixed. For the
>Pentax system, it's 45.5mm IIRC.

45.46mm to the focal plane (45.5 to the _rear_ of the film), at least for the thread mount system. Fortunately, since the lens focus is adjustable, you don't need to be exact (you can go shorter, but not longer, since you need to focus at infinity for astrophotography), but if you use a shorter distance, the focus distance indicator on the lens barrel won't be accurate.

Most CCD brands can attach via T-thread, so what you could do is put a standard T-ring on the lens, then use a male/male T-thread tube of the appropriate length. Alpine sells a short male/male tube, so you could use that with a T-thread extension. Note that Alpine (and Baader, the source of Alpine's parts) refers to T-thread as "T-2".

The "Russian" adapter converts to Pentax thread. The reference to "M44" on the Alpine site appears to be a typo. Both Pentax and T-thread are M42 (42mm diameter), but with a different pitch. T-thread is .75mm, Pentax/Russian is 1mm.

Edmund Optics also sells T-thread extension tubes.


Subject: Opposite of a T Adapter --part 4

From: Joe Shuster

From: John Mahony
>Most CCD brands can attach via T-thread, so what you could do is put a
>standard T-ring on the lens, then use a male/male T-thread tube of the
>appropriate length. Alpine sells a short male/male tube, so you could use
>that with a T-thread extension. Note that Alpine (and Baader, the source of
>Alpine's parts) refers to T-thread as "T-2".

John, the standard T-ring has T threads on the female side and proprietary threads on the male side. A Pentax screw mount lens will start to fit on the front, but it will seize before seating -- bad for the lens and the ring. And the male threads won't help Rod because he as a T thread female CCD.

>Edmund Optics also sells T-thread extension tubes.

If we're talking about most proprietary lens mounts, the T-thread extension tube is ok. However, it's important to be sure the lens has a "Manual" setting so you can adjust the f stop. Otherwise, the aperture stays open in "Automatic" mode for focusing and never gets closed for exposure. Also, for the Pentax screw mounts, the prices for used extension kits -- three different length tubes -- is ridiculously low. I've purchased a couple of sets on eBay where the shipping was more than the product. (For other systems, the costs are much more. Also, note there are automatic and manual extension tubes. See, I told you it was more complicated than just hooking up the lenses!


Subject: Opposite of a T Adapter --part 5    Top

From: Doc G

  • The C thread is 1" 32 TPI. It is an English thread.
  • The T thread is 42 mm 0.75 pitch. It is metric.
  • As I recall, the Pentax thread is like the old Leica screw mount thread which is 42 mm 1.0 pitch.

There are also a C bayonet standard and a small standard thread for web cams and the like.


Subject: Opposite of a T Adapter --part 6

From: Joe Shuster

From: Rod Cook
>The Pentax lens I have to work with are the bayonet type rather than
>the threaded type. In the past when I've thought about attaching these
>lens to a CCD camera, I've always thought I had to have a mounting just
>like the Pentax camera where you insert the bayonet tabs in the proper
>orientation, then twist the lens till it "clicks" into place. I liked
>Gary's idea about finding a junked Pentax camera for the lens mounting.

I was presuming you meant Pentax screw mount lenses instead of the Pentax K bayonet mount. So many of my comments are incorrect for your situation. For example, the adapter I cited was for fitting the Pentax screw lenses to a T thread. However, the comments about manual/automatic aperture opening are still very important.

Economically, the extension tubes for Pentax K are much more expensive than the Pentax screw system, as I mentioned. Your plan to use a junked camera is good if you have the tools to disassemble/destroy it.


Subject: Opposite of a T Adapter --part 7 of 7   Top

From: Radu Corlan <rcorlana_tpcnet.ro>

John Mahony wrote:
> I think I've heard that some metal rear lens caps will fit the lens well
> enough to be used as a starting point to attach to the lens. You'd have to
> cut a hole in the center of the cap and somehow attach a T-thread tube to it
> to attach to the CCD.

Another option is to look for a bayonet to c-mount adapter. On most, the bayonet mount part is detachable - and you get a good quality mount. I'm using the Nikon part from a Nikon to C adapter.


Subject: Eyepiece Projection Imaging      Top

From: Doc G

I have read some posts on the topic of eyepiece projection recently and am taking the liberty to make some observations about this technique. I have done quite a bit of projection imaging with microscopes and a bit with telescopes as well. I will discuss only positive projection here. Negative projection, such as with a Barlow, is limited to low projection powers and is often of poor quality.

My telescope experience has been mostly with projection of planets onto a video camera. While it is certainly possible to get good images by projection with an eyepiece, I think they are used mostly because they are there anyway. But it helps to think about the differences between visual observation of the telescope's real image and projection of that image.

Eyepieces are designed to be magnifying glasses and not projection lenses. They are designed to let you look at the real image that the telescope objective creates at the eyepiece position. They are basically a quality magnifying glass which is designed to have a large field of view. The eyepiece has special properties that observers seem to covet. One is as large a field stop as possible so that the actual field of view is as large as possible. The actual field of view depends only on the focal length of the telescope and the size of the field stop.

As an aside, one should note that the largest field stop possible is a bit smaller than the diameter of the eyepiece tube. Thus a 1 1/4 inch eyepiece usually has a maximum field stop of 28 mm. The reason for going to a 2" eyepiece is to get a larger field stop and thus see a larger part of the sky with a given focal length telescope. You can estimate the diameter of the field stop by looking into the back side of the eyepiece and hold a mm scale against it.

The compound (and complex) lens part of the eyepiece is designed to provide a view of the real image that the telescope objective creates at the field stop in a clear and wide field. This requires a design that has a large and flat field and projects a virtual image at some convenient distance in front of the eye. The power of the eyepiece is usually considered to be the focal length divided into 250 mm. The sharp edge of the field stop can provide a reference point for focus. But since the eye has considerable accommodation it is usual for critical focusing to have a cross hair or reticle located at the field stop upon which to fix the eye's attention.

The point of going on about these factors is that the optical design of the eyepiece requires large field and a curvature of field that fits that of the telescope. The real image is usually slightly within the focal length of the eyepiece and thus the projected image is a virtual image that the eye can see. (Note the eye cannot see a real image unless it falls on a ground glass or impinges on smoke.) Real images that need to be magnified by projection are not large in size. They are generally planets which have tiny but bright real images. One often looks at these with a short focal length eyepiece (a high power eyepiece). This type of eyepiece has a small field stop but that is fine since the image is small.

The idea of projection is to focus a real image (called the object) into another real image (called the image). In this case, the object is outside the focal length of the projection lens by a small amount and the projected image is outside the focal length by quite a bit so it is substantially larger than the original. To do this the lens used should be a projection type designed for a real object to real image magnification of about that desired. (usually 3 to 20 times) Lenses made for this purpose are microscope objectives, enlarger lenses, copy lenses, microfiche lenses, small format lenses, movie lenses, video lenses and the like. Some of these lenses are designed for specific magnification ratios and for flat but not necessarily wide fields. They are usually designed specifically for high resolution and high contrast. The size of the lens needs to be a bit larger than the object, that is the real telescope image, so that it intercepts the entire cone of illumination of the object. This is so that there be no vignetting.

Since the largest real image of a planet, Jupiter or Venus, is only 0.4 mm with a 2000 mm telescope, we are looking at very tiny images; even compared to a CCD chip. This is where positive projection works the best. Magnification of 3X to 10X will fill the CCD chip or video camera chip or even give a usable image on 35 mm film. Most books on photography of planets recommend, or hint at, using a lens other than an eyepiece for positive projection. (See references at the end of these comments.)

Ideal lenses for this application are small copy lenses or microfiche lenses. Short focal length photographic enlarger lenses and photomicro graphic lenses also very good. If an eyepiece is used, a simple orthoscopic type is better than a complex and costly wide field type. That is because the complex widefield eyepieces have too many glass surfaces and too much of the design is in reduction of field flatness and other visual qualities rather than projection qualities. The desirable lenses mentioned above are usually designed specifically for image magnification ratios of about 10 to 1. They are all of a speed of f4 or faster and thus will easily accept the object light bundle without vignetting.

Edmund Scientific is a source for high quality lenses of this type. There are other sources such as surplus optical suppliers. Some photo shops have selections of used lenses that are also suitable. You may need to have and adapter tube or some sort of holder ring made to mount them in the tubes you are using. Typically the microscope objectives are designed to work at a projection distance of 160 mm or so. So a 10X objective will be just about right for many purposes. Such an objective has a focal length of 16 mm. I personally use surplus microfiche lenses which can be found for only $20 or $30 each in focal lengths of 10 to 30 mm. They are very excellent for this purpose. You will find them in surplus optics catalogs.

Basically, the optical arrangement you want to use is to place the projection lens a distance of 150mm (6") from the imaging plane, that is the film or CCD chip and focus the telescope to place the real image in front of the lens at a distance slightly greater than its focal length. Believe me that for a very modest cost for the projection lens you will obtain projection results better that most eyepieces can deliver.

Several books that give good advice on these issues are:

Astrophotography for the Amateur - M Covington - Cambridge rev. 1991
Astrophotography an Introduction - HJP Arnold - Sky and Telescope 1995
Astrophotography II - P Martinez - William Bell 1987

I hope these considerations are of value to those wishing to do projection imaging. More info is available at my website.   Note: a blank browser window should open over this one.


Subject: Homemade Knife-Edge Camera Focuser       Top

From: Rob Roy <rroya_texeculink.com>

Description of a Camera Knife-Edge Focuser


-A body mount for your camera + screws (scrap from a local camera shop.)
-A 1.25-1.50" ABS reducer that connects the second kitchen sink to the main drain (you don't need the small seal that comes with it.)
-Three 1/4" 10-32 set screws (cup faced hold best in this instance.)
-Utility knife blade (2" long and /___\ shaped.)
-Short scrap piece of 1/16"-wall ABS pipe (usually comes in 100 foot coils.)


Close to the threaded end, 120 degrees apart, drill and tap for the set screws. You may have to file three flat spots to get close to the edge.


  1. Cut 1/4" off the threaded end. This becomes the retaining ring for the utility blade knife-edge. Cut two narrow kerfs on opposite sides for installing it into the female half later. (When finished it looks exactly like a slotted lens retaining ring in any lens or eyepiece.)
  2. Glue pieces of 1/2"-wide thin ABS scrap around the outside of the non-threaded end to thicken its end cross section. You may have to file any bumps off, first, to make it round and smooth.
  3. File the nooks and crannies on the face of this non-threaded end to accommodate the irregularities of your particular camera body mount.
  4. Drill small undersized holes into the face for the body mount (screws will self tap themselves.)


  1. Trace the outside of the retaining ring onto the back edge of the blade.
  2. Place the blade in a vise and snap off small pieces of the blade until its contour roughly matches the retaining ring.
  3. Put the blade into the female end against the collar and fasten it with the retaining ring. You may want to rotate it later (when you get the distance adjusted) to make it vertical.


  1. Take the back off your camera if that is convenient.
  2. Tape an ordinary razor blade across the inner rails so that the sharp edge is 6mm from the center of the frame. (If it is focused there and you have a slight bit of field curvature, then the center and the edge of frame should also be in focus.)
  3. If you wish, you can now measure the distance from the front of the body mount of your camera to the blade. You can preset your focuser close to that distance.
  4. Put the camera on the back of your scope and focus on a medium bright star until image blackens or disappears all at once as you sweep the k-e across it. (In an SCT you see a doughnut.) If it's not in focus, you see the k-e cutting into the doughnut from the left or the right side. You can use the camera's viewfinder to get the focus close, first.
  5. Replace the camera with the focuser and rotate the female end until you get exactly the same sharp blackening of the image.
  6. Evenly tighten the three set screws to hold it in that position. Double check it against the camera's focus.
  7. When mounting/dismounting the focuser from the scope, don't hold the female end as you may twist it and upset the adjustment.
  8. If you've already gone through all of this, you can figure out how to mount a simple 1" f.l. lens in a piece of ABS tube to use as an eyepiece. One of these makes the initial centering of the image and getting close to focus a little easier.


Subject: Camera Mount for LX200 URL    Top

From: Michael Cook <michaeljcooka_trogers.com>

I use a home made "cradle" to hold the video camera. The cradle is held in place by the threaded adapter ring at the cassegrain focus. My video camera has a fixed zoom lens. As such, I use the afocal method to get an image in the video camera. See my web page under Telescope/accessories at:

   Should open a new browser window over this page.


Subject: Meade f/3.3 vs. Optec Maxfield    Top

From: Chris Vedeler <cvedelera_tix.netcom.com>

I just finished an article comparing the Meade f/3.3 focal reducer to the Optec Maxfield in side-by-side tests.
Take a look at: http://www.isomedia.com/homes/cvedeler/scope/focal_reducers.htm
Note: should open a new browser window over this one.


Subject: Meade f/6.3 Reducer Spacing      Top

From: Don Tabbutt <dona_ttabbutt.com> Date: Feb 2002

With regard to focal length, Dennis di Cicco addresses this very subject on page 38 of the June, 1997, issue of Sky & Telescope. He even provided a chart and tabular table on compression versus distance from the rear mounting flange of the reducer to the focal plane.

He states that the Meade f/6.3 reducer is designed for 105mm spacing. That is, at that spacing, the reducer will deliver a compression ratio of 0.63. However, the reducer can also be used at other spacings, which, for the most part, simply modify the compression ratio.

For example, on an 8" SCT, a Meade f/6.3 reducer can be spaced anywhere from 70mm to 225mm from the focal plane. The effective compression ratio varies from .7 to .5, respectively. This means the chip in your camera can be more than 8" from the reducer and still work, nicely accomodating your focuser and flip mirror.

Matching threads is an issue he didn't address, but I can tell you I go from the reducer to the flip mirror to the 416XTE with no step rings. You may need some with the NGF-S in the mix.


Subject: Deepsky Imaging and Alt/Az?  Top 

From: Joe Shuster <jshuster42a_tcomcast.net> Date: Nov 2003

-----Original Message-----
From: Sylvain
I know that some people use a derotator in Alt/Az. Is it really necessary
for 5 min exposures? Doesn't it add a supplementary "PEC" problem?
Isn't it just enough to rotate individual images when registering them
with proper software?

Long exposure in Alt/Az isn't easy to do without real-time compensation. You can rotate multiple images using software, but even in a single five minute exposure, you'll see unacceptable rotation at the corners of the field. The rate of field rotation is a function of latitude and the Alt/Az coordinates of the object. Check out:

  <http://www.ghg.net/cshaw/guiderot.htm> for a formula and chart.

Editor's note: also see the topic of Field Rotation.


Subject: Digital Camera Adapters  Top

From: Jordan Blessing <jblessina_tworldnet.att.net> ScopeTronix Astronomy Products 

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

In regards to using a Digital Camera with the LX200... We manufacture a very versatile bracket that will allow you to connect most all digital cameras to most standard sized Plossl eyepieces. If you take a look at the "Astrophotography Access." button on our page you'll see it mounted on an ETX and a Tak, there is also a link to some pretty good pics taken with it by Paul Walsh. We will also soon be carrying a number of adapters for the few digital cameras that actually do have a threaded ring around the lens. If your digital camera does not have manual override of the controls you will be limited to the Moon, Sun, and Planets, but it is still quick, fun, and easy (at least compared to long exposures)! Most digital cameras have a timer function to allow you to get into the picture, this works great with a telescope. Just line up and focus, set the timer and get your hands off so the shakes have a few seconds to dampen before the shutter fires.


Subject: FITS Image Viewers    Top

From: Michael Cook <michaeljcooka_trogers.com> Date: Sept., 1999

I came across a couple of image viewers with some impressive processing features. These are freeware. IrFanView and XnView are available through <http://www.tucows.com/> - under Win95/98 image viewers. Note: should open a new browser window over this one.

XnView has FITS support which makes it nice. I now use these with ECU to view images of objects. The nice thing about XnView is that I don't have to convert my ccd images which are in FITS format.

BTW, in PictorView user set up, there is a choice between FITS version 1.1 and 1.2. What are others using? I'm off to the FITS office to read up on this, but what are the differences to PictorView?

Get ECU User Object Files - <http://members.rogers.com/michaeljcook/>


Subject: Astrophoto Math      Top

From: Mark Florian <mfloriana_twans.net>

To determine the lunar image size with a particular lens or telescope, divide the focal length in mm by 110 to arrive at the lunar diameter in mm on the film.

To find the image size on your film in mm of any object in the sky:

(Object in degrees) x (focal length in mm) / 57.3 degrees

If you have a calculator with the tan function, then take the tan of the object in degrees and multiply by the f.l. of your scope (or lens) in mm.

For the moon: tan .5 degree = .00873.

My Ranger has a FL of 480mm, so .00873 x 480mm = 4.19mm. I find this procedure quicker than working in inches.

Some of you may recognize this as the true field formula rearranged:

(Field stop dia. in mm) x (57.3 degrees) = True field in degrees in sky

Finally, by converting the size of your film to degrees based on your focal length, you can quickly decide if an object will fit. A 35mm negative measures 24mm on the short side & 36mm on the long side. So taking each side in turn:

24mm x 57.3 degrees = length of short side in degrees F.L (mm)
36mm x 57.3 degrees = length of long side in degrees F.L. (mm)

Thus for my Ranger, a 35mm negative will record 2.9 deg. x 4.3 deg. If I use a 2X teleconverter on my camera, the field size drops to 1.5 deg x 2.2 deg.

If you have a 2000mm Schmidt-Cass, you can record only 0.69 x 1.03 degrees.


Subject: Tokai Light Pollution Suppression Filter    Top

From: Greg Hartke, <ghartkea_tclark.net> Date: March, 2000

Those MAPUG subscribers who hang out on APML are already familiar with the Tokai light pollution suppression (LPS) filter but I thought I would pass along a few observations of my first efforts using this filter.

I've used the 48 mm Orion Skyglow filter and (as I'm sure many others have discovered) noted that it gives a red cast to color slides taken thru it. I understand that results with the Lumicon broadband filter are similar.

Keep in mind that these filters work and work well: I've taken some 1 hour shots that have *no* problem with sky fog. They do, however, show the dreaded reddish cast mentioned above, anathema to someone who shoots slide film and has no means of performing any image processing. For someone who routinely scans and processes their slides, this is less of an issue because the background color can be removed leaving a fine looking shot. (I this can be done because I sent a few of these to my brother-in-law to play with and he removed the background with very pleasing results.) The background is, however, rather unesthetic when viewing the unenhanced slide.

To those who have not heard, the Tokai LPS filter is (as far as I know) a relatively new item that is rather different than the light pollution filters we've seen before. The typical broadband filters remove a fairly substantial swath of the visible spectrum. Most of the visible spectrum is confined between 450 and 650 nm; the Lumicon Deep Sky filter basically blocks transmission from approx 535 nm to 615 nm, an area of the spectrum that has many of the lines associated with typical municipal lighting using sodium and mercury based units. Clearly, this is a substantial reduction from the full spectrum. (The Orion Skyglow is similar, though no doubt different in detail.)

The Tokai LPS filter takes a rather different approach. It actually suppresses transmission around a series of wavelengths centered at 405 nm (a mercury line), 436 nm (another mercury line), 546 nm (still a third mercury line), and a block of lines thru 570 nm (sodium), 579 nm (mercury), 583 nm (sodium), and 600 nm (sodium). It also suppresses transmission of a line at approx 630 nm, but I haven't been able to identify the source of this line. In any case, the point is that the filter provides some transmission in the 535 nm to 615 nm range that is usually completely blocked by other broadband light pollution filters. I would prefer that the blocked portions of the spectrum were narrower (a transmission plot is included for your particular filter when you buy one), but I expect this couldn't be done nearly as easily or economically.

The effect of this more selective blocking? The makers claim very good suppression of sky fog in areas with typical light pollution problems while doing a good job of maintaining color balance. Does it work? Betcha dupa it works. In spades.

I sold my old 48 mm Orion Skyglow and 1 1/4" Lumicon UHC on Astromart and proceeded to buy one of these puppies to see what it would do. I bought the 48 mm size since that accomodates the 2" size I use for all of my accessories. (The 2"-to-T adaptor I use for astrophotography vignettes considerably less than a 1 1/4" adaptor would.)

The skies at my house are nothing to write home about: Approx mag 5.5 in the dark parts of the sky with plenty of glow near the horizons and in particular directions. I have what would be considered decent suburban skies, though I'm plagued by a couple of street lights near me that confine me to the area on the deck directly behind my house. Shooting thru my 10" f/6.3 LX200 (there we go, a little MAPUG topicality at last ;) ) at prime focus with Kodak Elite Chrome 200 push processed 1 stop, I find that sky glow is typically noticeable after 20 minutes and objectionable at 30 minutes. It can be *very* objectionable at that time or not too bad but quite noticeable, depending on many factors. (Temperature, dew point, direction, time of night, etc.)

Concrete examples:
I shot M79 (globular cluster in Lepus) for 20 minutes w/o filter, 50 minutes w/o filter, and 60 minutes w/LPS filter. South is not a good direction for me: The 20 minute shot showed yuck. (Please forgive the technical terminology...) The 50 minute shot showed a lot of yuck. From a sky glow standpoint, the 60 minute shot with filter is *much* better than the 20 minute shot w/o. It also is a much deeper shot. (No surprise there but it's hard to quantify a filter factor here without careful controlled testing which I am making no pretense of doing yet.)

M1 shot for 50 minutes was downright ugly without the filter. M1 shot for 60 minutes with the filter demonstrated absolutely enormous improvement -nice colors in the nebula and a pleasing background.

I shot M81 and M82 for 80 minutes. *Very* cool. M82 showed lots of color, M81 an amazing amount of detail, and the background is nice and dark. (That shot might really be neat with enhancement. I'm also thinking stacking. Soon. Soon...) M51, 80 minutes: Amazing amount of detail. What sky fog? Oh, all right, there's some but it sure isn't very much. M104 (the Sombrero - I'm excited about the coming galaxy season) was quite remarkable. I couldn't believe how dark the sky background was for an 85 minute exposure in that part of the sky. (Of course, according to my notes I started that shot at 2:20 AM and it was actually noticeably darker at that hour than it was earlier - I assume this is because a lot of outdoor house lights are turned off by then. I've noted this before. Fewer cars out, too, and that might make a noticeable difference in sky glow.) I shot M65 and M66 in Leo for 90 minutes, and that pic came out very nicely, too. M3 in Bootes, 60 minutes and 90 minutes: Ditto.

I also now have a 90 minute shot of IC434, NGC2024, and B33 (the Flame Nebula and the Horsehead Nebula in Orion) that might raise some eyebrows. Well, it raised mine but I'm easy.

Take note that all of these assessments were made *without* image enhancement of any kind. I was looking at the bare slides. The difference in the raw film strip between shots with and without the filter was immediately noticeable. I have my slides processed, then cut and mount them myself. The difference in background level between the shots w/o filter and those w/LPS filter has to be seen to be believed. It's actually a lot harder to cut the slides accurately where the filter has been used because the background is so dark. I expect most of you would have to look at the strip yourself and see the difference to believe it.

The bottom line, folks, is that someone trying to shoot in any light polluted area likely *must* have one of these babies. For me it's now an absolute must: I wouldn't be without it. Let me reiterate, though: The typical broadband filters work and work well. This new filter is, however, much better suited to photography because it does not obviously affect the color balance. This is particularly useful to those who do slide work and who don't scan and process their own pictures. Those who routinely scan and enhance their pics (especially those who shoot color print film) may not need it as much as those of us who must do without.

No doubt some will want to know the particulars for ordering the Tokai LPS filter. The distributor is Hutech Corp. of Torrance, CA. The URL is:

<http://www.sciencecenter.net/hutech/> Note: should open a new browser window over this one.

There you will find examples of pictures with and without the filter (taken by Mike Cook, if I recall correctly), transmission characteristics, and pricing and availability information. The 48 mm filter I have (they come in many sizes) was $189 + $8.75 S&H. I dealt with Mr. Ted Ishikawa <ishikawaa_thutech.com>, who was extremely polite and helpful.

I should mention (because someone is bound to ask) that I really haven't gotten interested in doing any visual testing. I know it sounds weird, but I can't get too excited in observing DSOs here in my not-especially-impressive skies after having spent years using better instruments in much darker skies. Call me jaded. I'll let someone else pick up that ball.


Subject: Focal Point Focuser    Top

From: Guido Pasi, Genova, Italy, Date: March, 2000

>I have seen a product called Focal Point that is made
>in Italy but have no clue how to contact the manufacturer..

FocalPoint is made by Laborfoto SRL - via Marini 1 - 30030 GARDIGIANO (VE)- ITALY -
   e-mail: <Laborfotoastronomiaa_tshineline.it>

Today I phoned to Laborfoto and they answered me that they still make it and have no problem with sending to the US.

I did not understand from your private e-mail that you need help: my English is not so good...but I speak Italian! so if you (or anyone else) need assistance I will be very glad to help you with the manufacturing (anyway they probabily speak English).


Subject: MAPUG Observatory Site for Posting Member Images Top

From: Don Tabbutt <dona_ttabbutt.com> Aug., 2000

I have put together a web site that will eventually be the MAPUG Observatory for members to display their work who don't have their own web site. Contact me directly for procedure to submit your images and information about them. The site can be viewed at:



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