Miscellaneous Items

       

Subject: Experiences with the Lumicon Giant Rich Field Viewer

From: George Malyj

>>>I was wondering if anyone has the Lumicon Giant Rich Field Viewer (akin to the GEG but without the guiding part). I have a 10 inch LX50 with TV 2" mirror diagonal and SCT adapter. Do I need any other kinds of attachments to fit this reducer into my set up, also can you vary the focal ratio the way you apparently can with the GEG.<<<

I have the Giant Rich Field Viewer (GRFV), currently $250 from Lumicon, and use it for visual only on an AltAz-mounted 10" f/10 LX200. I believe your TV 2" mirror diagonal has the same 2" OD front barrel as my AP Maxbright, so it will fit directly into the back of the GRFV; no need for the SCT adapter.

The 10" and 12" Meade SCT OTAs have an approx. 3.25" ID threaded flange on the back end of the optical tube that screws off, exposing the primary baffle tube. Since I have one of the early (1992) "unbaffled" baffles (!), the fully-illuminated circle exiting the primary baffle tube is about 2.3" diameter. I believe it's more like 2.0-2.05" diameter in the newer baffled 10" OTAs. The standard SCT visual back has an ID of only 1.5", thus severely vignettes the light path if left in place. Lumicon makes a 3.25"-to-2" adapter (a $59 accessory) which, using 3 brass set screws, allows you to easily interchange between the GRFV and direct f/10 viewing with 2" OD barrels. In other words, you can quickly remove the GRFV and insert your TV 2" diagonal directly into the adapter, holding it in place with the 3 brass set screws instead of having to deal with screwing and unscrewing the various SCT back-end adapters when you switch. The 80mm diameter achromatic in the GRFV gives excellent center-to-edge views with the 35mm Panoptic (pinpoint stars over most of field, slight coma near edge of FOV), but does introduce aberrations and a bit of color that become evident with high-power eyepieces. So strongly recommend getting that adapter for quick switches back to f/10 for medium-to-high-power viewing.

So, you're wondering how wide a field do you actually get with the GRFV? As others have pointed out, f/10 SCTs gain a bit in focal length when you introduce the longer light path of a 2" diagonal vs. straight-thru eyepiece views. I calculated mine at f/10.4 with the 2" diagonal, yielding a true FOV of 54' and 75X magnification using a 35mm Panoptic. With the GRFV's 80mm achromatic in the rear position (closer to the eyepiece) the true FOV increased to about 78'. Moving the achromatic to the lens-forward position, which is how I use it, the resulting (about f/6.2) system with GRFV, 2" diagonal and 35mm Panoptic yields a true FOV of 90' and a magnification of 45X. I looked at blue sky in daytime as well as drifted star clusters from center to edge and could not tell any noticeable vignetting across the 1.5 degree field of view. However, you may have some vignetting near the extreme edge in the lens-forward position if your 10" is a newer baffled OTA as noted at top. Your actual true field will be considerably greater than with Meade's or Celestron's f/6.3 reducers because both of those have limited 1.68" apertures paired with the 1.5" ID of the standard SCT visual back adapter. BTW, the GRFV can be converted into a GEG with a parts package from Lumicon should you decide to do guided photography in the future.

Items of caution. First is your eyes. If you have astigmatism in your viewing eye, it may be barely noticeable at the 3.5mm exit pupil of a 35mm Panoptic used at f/10, but really affect star images at the 6mm exit pupil of the GRFV in lens-forward position. Affect the view enough that you may need to wear glasses to correct for the astigmatism and thus limit your ability to see that wider field. Most eyepieces perform well at f/10 but some not so good at f/6, so that may be a consideration if you don't have the 35mm Panoptic. Don't even think of using a 55/56mm Plossl with the GRFV; a 35-40mm f.l. eyepiece is really the max. Another consideration is that the background sky is naturally brighter at lower power. If you do not have a regular dark-sky site and most of your viewing is done from urban/suburban skies, you may decide the aesthetics of that brighter background make the view less pleasing at lower power. Next, forget about swing-through on an LX200, and would assume on an LX50 as well. The GRFV adds >4" length to the back of the OTA, enough so that with the 2" diagonal hanging off its back the diagonal contacts the base when the tube is pointing 11 degrees from the zenith in AltAz set-up. So you folks with LX200s need to watch your GoTo selections so that your diagonal doesn't slam into the base and fries your Dec motor! Stay away from the zenith in AltAz and the Pole if using a wedge. Counterweighting mandatory. A GRFV, 2" diagonal, and 35mm Panoptic combine for a lot of weight on the eyepiece end.

If you can live with the above and have a dark sky site to view from, I think you'll really enjoy the wider fields. M31, M33, Double Cluster, Pleiades, etc. better-framed. Two decades ago I owned an unwieldy 10" f/5.6 Newtonian that was impossible to properly balance on a way-undersized GEM mount, but I did miss having the rich fields when moved to an f/10 SCT. Now I can have that 1.5 degree wide field on a 10" aperture, yet takes only a minute to release set screws and switch back to f/10 for regular viewing.

Subject: Magnitudes, Mirror Sizes, and Reflectivity's  

From: Robert Preston

We've had some back-and-forth about magnitudes and sizes and coatings lately. I've learned some surprising facts during the process. Most recently, someone (sorry, can't access the name at the moment) pointed out the actual magnitude difference observable with 96% vs. 89% reflectivity (a single mirror, ignoring the secondary). If I've recalculated that number correctly, it amounts to 0.082 magnitudes - almost no difference at all, on a magnitude scale. Even throwing in a second mirror and comparing (0.89 x 0.89)= 0.79 vs. (0.96 x 0.96)= 0.92 system reflectivity, the magnitude difference is only 0.167!

Suppose I let secondary smoke, oxidation, and other crud accumulate on the mirrors so the reflectivity drops to 70% on both primary and secondary?

delta mag = 2.5 log (ratio of brightnesses)
	 = 2.5 log ((0.96 x 0.96)/(0.70 x 0.70))
	 = 0.68 magnitudes.

Well, I guess I might lose one or two moons of Saturn, then, but my 8" tarnished scope will still be good enough to let me put off recoating for another year or three. The formula for delta mag vs. brightness ratio is simply the definition of "magnitude" - a five magnitude difference is defined as a brightness ratio of 100. Or, brightness ratio = 100^(delta mag/5), which rearranges to the first equation, above, when the log of both sides is taken and the algebra is done

Subject: Adaptive Optics for Refractors? --Part 1 of 2    

From: Michael Hart, Date: June, 1998

> Is it possible to get adaptive optics on a refractor?

> Well, ah, yes you can, but I doubt you would want to. SBIG's

> unit looks just like a standard star diagonal. The mirror

> tilts on two axis to provide the AO action. It will work

> with any OTA that has enough back focus.

> Most refractors are short focal length wide field instruments.

> Since the focal length is so short AO will not materially improve

> the image - although it can compensate for a bad mount. AO

> really shines on improving images taken through a long FL instrument.

> SBIG's AO bolts to the front of the camera and has a standard

> female t-thread opening in the front. If you can mount a camera

> to your OTA you can mount the AO. The biggest problem, as I

> mentioned, is back focus. If you are planning on using a

> focal reducer there is a very good chance that it won't work.

> > Gene Horr <genehorrswbell.net>

Gene does a great job in describing the AO-7 accessory. I have quoted Gene's entire post because I believe it will help those considering the AO-7 accessory for their LX200 or refractor make an informed choice. I believe the term "adaptive optics" sometimes used for the SBIG AO-7 unit may also lead to some confusion as to the results one can obtain from this accessory and when it is appropriate to use. First, the AO-7 will not compensate for poor seeing. The AO-7 appears to like 2 arc second seeing or better before improvements over a good mount start to show. Most of us (except the lower Florida area and mountains such as Mt. Pinos) do not experience 2 arc second seeing very often. Adaptive optics in large observatory scopes such as the WIYN use large quantities of computer controlled hydraulic actuators under the primary mirror to alter (adapt) the mirrors figure corresponding to the patch of sky seen by the optics, often aided by secondary tip-tilt mirror systems and lasers which can place a bright "guidestar" where needed. The AO-7 does not perform in this way, rather it is more like a really fast autoguider controlling a low inertia mechanism (a first surface mirror flat controlled by X-Y voice coils) which enables a fast guiding correction response time with minimal backlash. For brighter guidestars, the corrections possible approach 30 Hz., though I have seen values reported as high as 50 Hz. At the focal lengths where the AO-7 works best, a moderately bright to dim guidestar is more likely found, limiting the guiding correction speed. The Hubble GSC along with a field of view overlay showing the guiding chip location is useful to select the most appropriate guidestar for the AO-7. In this way, one can orientate the AO-7 to a brighter guidestar resulting in faster corrections. As we lower the focal length, the distance from the guiding chip used to control the AO-7 accessory and the imaging chip (as related to patch of sky) seen by the chips increases. A fast guiding correction required to return the guidestar centroid to position may not be needed or is even incorrect for the imaging chip. As a result, as we lower the focal length, the potential for improving atmospheric blurring decreases rapidly.

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

Subject: Adaptive Optics for Refractors?--Part 2 of 2    

From: Gene Horr <genehorrswbell.net>

> Hi Gene - thanks for the information. The focal length of the 7"

> APO is 1600mm, so do you think this is too low for any worthwhile

> expense? Why is it that the AO only works with longer focal lengths anyway?

You might notice a slight improvement. With shorter focal lengths the resolution is much lower. Example: A .5 arc-second improvement in "seeing" is much more dramatic at 3,000mm FL where each pixel of a ST-7 covers .6 arc seconds versus 1,000mm FL where each pixel covers 1.8 arc seconds.

(Note: I am not saying that the AO will improve "seeing" by this amount, I am just throwing out numbers as an example). Now, in my opinion the improvement in resolution due to the AO fighting atmospheric effects ("seeing") is highly overrated. It does result in am improvement, just not as much as the ads would lead one to believe. It is much better to think of it as a backlash-free drive corrector. If you are detecting errors in your mount *THIS* is where the AO really shines. The AO runs ~US$900 shipped, but keep in mind that it only works with either the ST-7 or ST-8.

Subject: Language Translator URL 

From: Pat McGuire

Perhaps I can suggest MAPUG members who are having difficulty with foreign language translations etc. access the following web site:
   <http://babel.altavista.com/tr?>
     Note: should open a new browser window over this one.

I find it does an adequate job on most all my translation needs and can be used with both e-mail and web pages. Using this site, you can now access all those European web sites featuring Meade advanced products.

Subject: Spectrograph Sources --part 1 of 2 

From: Matthew Ganis

>Does anyone knows any spectrograph manufacturers
>that fits amateur size telescopes? I've searched and
>found only models that fit the "big ones"...1.2 meters min.

Check out Sivo Scientific at :

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

I bought one about a year ago and I'm VERY happy....

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

Subject: Spectrograph Sources --part 2

From: John Teel <mapuglist2yahoo.com>

Try the following link. I don't have any experience with this unit but ran across it a while back and bookmarked it for future use since I plan to someday get one.

  <http://www.optomechanicsresearch.com/10c.htm>
    Note: should open a new window over this one.

Subject: Controlling Streetlights w/Laser 

From: Ricky Cain

The laser needs to be one that can shoot over 1600 feet, because it has to have a good size splatter of light on the sensor. When I first tried doing this I had the same problem the light kicking back on after a few minutes. Correction of several problems has solved the issue and the light stays off for as long as I want it to now.

The first problem was that I didn't have an accurate idea of where the photo cell for the light was located. There is usually a plastic or metal cover around the sensor with an opening where the cell is located. The laser needs to be pointed exactly (to a degree) at the sensor and directly in front of it if possible. An angled shot always make the light come back on. I use binoculars to make fine adjustments and get the light concentrated on the sensor. The laser attached to a tripod (I used Velcro) accomplishes this need for accurate pointing and it keeps the laser very still. Also, the tripod needs to be securely set up. It took a while for me to determine the need for this adjustment but, I finally noticed the tripod the laser was mounted on was "bleeding" down and thus moving the laser just enough to kick the light back on and screw everything up.

Subject: Eyeglasses for Observing  

From: Paul Rodbell

Franel Optical has an amazing variety of possibilities:

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

R. A. Greiner wrote:

> The glasses are "Franel - Double view" They have double frames so you can use a pair of
> lenses with no lens or a pair of lenses with another pair. This gives you great versatility.
> You can have far correction and then near correction with a flip of the second
> lens set or any other combination you would like. They are very well built (seem to be designed for heavy use)

Subject: Pupil Size vs. Laser Vision Correction  

From: Ed Cannon <ecannonmail.utexas.edu> Date: May 2003

>... recent research on large pupil size (night vision)
> problems with laser vision correction. Read it here:
> <http://www.eurekalert.org/pub_releases/2003-05/uorm-dfo050603.php>

I know someone very well who had laser correction surgery and now has some night-vision problems due at least in part to her pupils dilating to a diameter larger than the treated area.

Here's another informative article about the laser surgery and night-vision issue:
   <http://www.refractivesource.com/doctors/clinical_pearls/role_pupil.htm>

Some months ago I read that in Canada the standard size of the corrected area is 9 mm and that they tend to have better night-vision outcomes there than here where the standard is only 6 mm. That article said more or less that people who are very satisfied with their night vision probably should avoid laser eye surgery.

Another problem I can easily think of is getting the surgery and then ten years later finding out you have to wear (reading) glasses anyway due to presbyopia.

Subject: Thread Specs for Misc. Telescopes & Accessories  

From: Roger Hamlett <ttelmahntlworld.com>

This is a list, of some threads used in telescopes and accessories. Some are 'from specifications', while others have been taken from measurements. There are also some notes about 'oddities', with some parts, and in a few cases other data covering such things as the design 'focal plane' distance. If you have additional specs or corrrections, please contact me.

Meade:
Rear Port on 10" and larger models (excluding the C16) 3.25" * 16TPI
  2" SCT 2" * 24TPI
  ETX Rear Port 1.375" * 24TPI
This is to me, an 'oddity', since in general Meade threads are imperial, but the external measurement, seems to be fractionally 'oversize', and the thread is really closer to 35mm OD.

Celestron:
  Rear port on C11 C14 etc. 3.3 * 16TPI
Many of the scopes outside diameters, measure slightly 'small', at about 3.29", but cutting to 3.3 for the outside of the thread teeth, gives a good fit, with reasonable clearance.
The rear cell on the smaller scopes, and on the rear of the adapter attached to the larger scopes, is the 2" SCT thread above.

On the 1.25" 'visual back', the external thread, is:1.38" * 24TPI
This is very close to the thread on the ETX, but is very slightly larger. The relationship of these two threads, is definately an 'oddity'. In most cases, accesories for each, will fit the other, provided they are slightly 'oversized' on the Meade fitting...

General:
  M42/Pentax. 42mm * 1mm
This is the thread on the older StarLight camera noses, and on quite a few odd accessories.
The focal plane, is meant to be at 45.46mm from the camera face (45.5mm to the _rear_ of the film on a normal camera 'body').

  T42 42mm * 0.75mm
This is the thread on the extension tubes supplied by Meade/Celestron, for their focal reducers, on the rear of some OAG's, and on a lot of camera attachments. The newer Starlight SVX-H9 family have this thread.
This is the thread normally called simply the 'T' thread. Beware though, that a lot of accessories that refer to a 'T' coupling, may use the alternative 'T bayonet', so make sure you are dealing with 'T-threaded' accessories when buying parts...

CS 1" * 32TPI
This is the thread found on some WebCams, and on the Starlight guide camera for the SVX. The focal plane, is meant to be at 12.5mm from the face.

C 1" * 32TPI
Identical to the 'CS', but with the focal plane at 0.69" from the nose (17.526mm).
The commonest 'webcam' lens thread, is 12mm*0.5

Filters:
  1.25" eyepieces. These take filters measuring 28.4 * 0.6mm
This is another 'oddity'. Technically, there is a standard for camera filters, which are 99%, in 1mm (or occasionally in 0.5mm) steps, with pitches of 0.6mm, 0.75mm, and 1mm, according to size. The version used on telescopes, is (I believe), an imperial 'conversion', which has been modified to bring it 'in line' with the filter standard. I suspect the 'orginal', was: 1.125" * 42TPI.

There are a couple of old 'Leica' filters, which show this same 'between the steps' sizing.
Occasionally, some old filters turn up, which are very 'tight' in the modern threads (the imperial measurement, is 0.007" larger).

  2" eyepieces. 48mm * 0.6mm
Again there is an 'oddity' here. Generally, on threads, the 'bore' is cut to the specified size, and the thread to fit inside is made a few thousands of an inch 'small', to give a comfortable fit. Some Meade 48mm filters, seem to be made with this thread slightly 'oversized', making them unconfortably tight (to the point where in some cases they won't fit...), in some other makes of eyepiece. Beware....

Others:
Takahashi, use an assortment of 'unusual' threads. So their eyepiece extension tubes, use 43mm * 0.75mm. The 'Rear Port' , on their scopes, is normally 72mm * 1mm.

Borg use a similar (even larger!), assortment of threads, offering adapters to many other makes, as well as their own variants. Fortunately, they publish a good list of the threads available, at:
   <http://www.sciencecenter.net/hutech/techdocs.htm>

The 'component catalogue', gives the thread sizes for each end of the adapters in their range of products, including, the thread sizes used to fit many other makes of scope (Takahashi, Televue, Vixen etc,). This is therefore a 'gold mine' for anybody wanting to make adapters. :-)

'Base' threads & Camera tripod:
  1/4   * 20TPI. This is the thread in the side of an SBIG camera, and also in the base of ETX scopes.
  5/16 * 18TPI. This is the thread in the top of most Meade/Celestron tripods.
  3/8   * 16TPI. This is the thread into the base of several scope (the LX200, and the Celestron C11 for instance).
  1/2   * 13TPI. This is the _centre bolt_, on the LX200 models.

Generally, all the imperial bolts are 'UNC' tooth form (60 degree). The metric threads are also this shape.

Subject: Gear Vendors     

From: Michael McNeil

Great news, I found the company that supplies some, if not all gears, and bearings to Meade, Celestron, Parks, and some others. They even have anti back lash gears, that can replace gears in Meade, a problem I read about on here!. Also they have the replacement Ball Bearings for Meade, like flange ball bearings to replace the oil lite, and also, Nylon. They sell to Meade?

W. M. Berg Inc., 1-800232-BERG, Address: 499 Ocean Avenue, East Rockaway, NY 11518
Web page address : http://www.wmberg.com/ -- From: Michael Conte mcontecrosslink.net
    Note: should open a new window over this one.

The have 2 catalogs. One main with inches, etc., and another in metric. Ask for both. Just my new shaft and worm gear, and ball bearings for the Compustar, No jerky motion in the DEC now. 4 ea. shafts both Dec and RA, spare rib timing type belts from motors to worm gear shaft gear, and worm gears, and 4 set of bearings for all,, $24.70 and they opened an account for me, as they know that Celestron or Epoch Ist, can no longer back up at all the Compustars. Hope some of you find this product line useful, and after seeing the Meade gears, I wonder why they didn't spend a few bucks more to do it better, like even the bearings, 15 cents difference in large lots???

I should of also said, that you won't be able to just ask for replacement part, you'll need to figure out the size of the bearings and gears your self, or ask Meade, what is this, teeth count, pitch, shaft size, etc. Don't expect Berg, to know this, they don't and I'm sure the sales person that handle special accounts has orders not to give out info, as they did with Compustar. I had to get some of the info from my friend at Epoch, who made the Celestrons into the Compustar, the rest I had to figure out, but no big deal.

Subject: Meade 500 Series Mount Dec Axis Upgrade  

From: Jeff Mammele

An idea I've had for months, to make DEC axis move smoother. I'll try to keep this short as possible.
Mount: Meade 500 series.

It involves using 1/4" ball bearings. I tried it many times before, but could never get it right. Last night (in a vision) it came to me. There is a center bolt that the axis turns on. I took off dovetail plate that holds OTA. Then you see the nut that holds the bolt. It has a set screw in it. (the nut) Take that off, then you can pull top part of DEC assembly off. (carefully) inside it is round (of course) The outer most part is divided by a wall (you are looking down into DEC axis) ball bearings fit perfectly in this outer grove. The top assembly sits on top of bearings, when putting back together.

When I did this before the bearings naturally makes the top assembly sit up a 1/4" higher. The bolt wasn't long enough to put nut back on. Damn.... Then, my revelation. Get a longer bolt! I went to hardware store, they had 1 exactly the right size! It was a bit more difficult for me because the DEC encoder (for computer) fits on the top of bolt inside the front opening. You know, take off that plastic cap. That is where a polar finder would go. Look up inside to see top of bolt.

I had to take encoder out, then unscrew the counterweight shaft (it has a tiny Allen screw) on front of it. Once I got shaft off I had enough room to take out bolt & put longer 1 in. Then it was just a matter of putting everything back together.

Before I put top of DEC assembly back on I sprayed bearings with a graphite, silicone spray. There is a gap (of course) but who cares!

I then put dovetail plate back on & gave it a spin (make sure cord to drive motor is out) IT spun around like there was no tomorrow! Then the real test. Put on OTA. I couldn't believe it! I SWEAR, I could almost make it spin by blowing on it! I'm still in shock. I'll bet it could handle twice the weight now. The bolt, ball bearings & can of spray - $12. Took less than 2 hours. Course I was really taking my time. Gives my NGC-MAX 100% accuracy! I realize it's a cheap mount, but it moves more freely now, than any high-end mount I have ever used.... Perhaps the application could be used in other (not user friendly) mounts.

Subject: Used SCT Buyer's Guide & History of the SCT

From: Jack Estes <jackesteshotmail.com> Oct 2001

This is a .pdf download: <http://skywatch.brainiac.com/sct-user/usedSCT.PDF>

Subject: Is Lunar Observing Better with Larger Meade SCTs? --part 1 of 3  

From: Roger Hamlett <ttelmahntlworld.com> Date: Nov 2003

> Does anyone on the list regularly observe the Moon with the
> larger (10" +) Meade SCTs?
> I own a Meade ETX-90/RA but wonder if the large telescopes
> produce excellent images with regards to the Moon. I have
> heard that SCTs in general are not that good for the Moon
> due to the central obstruction lowering the contrast. I find
> this hard to believe as I get good views with my 90mm Mak.
> Which Meade scope would be the best for observing the Moon in detail?

In all honesty, what you can see, varies with the weather, more than the scope!...

The 'downside' of obstructed scopes, is as you say, that the central obstruction moves a small amount of the light from the central 'peak' of the Airy disk structure, out into the surrounding rings. However the amount is often overstated, with wild claims, such as people saying that a 4" unobstructed scope is as good as a much larger obstructed scope. In all honesty, if people are seeing an obstructed scope perform this badly, on a reasonable night, then there is something wrong with it (usually collimation, which is very critical for observing fine detail). However see the comments below about the atmosphere. The old 'rule of thumb', which gives results very close to the values you get if you plot the MTF of the scopes, is that you simply subtract the secondary diameter from the primary diameter, to get a good estimate of the 'comparable' unobstructed refractor. Realistically though, as the scope gets larger, the number of occasions when the sky will allow anything close to the resolution to be achieved, falls. This is why so much successful imaging of Mars on it's recent closest approach, was done using webcams. The imagers, took often thousands of frames, and then 'threw away' a large percentage where the atmospheric disturbance was bad, and averaged the better images. Your eyes will perform a similar function (to a somewhat lesser extent), with persistence of vision, allowing you to see detail from the momentary 'good' flashes. The webcam approach, because of the sheer number of images involved, will (if properly done), give finer images, than your eyes manage (unless you have one of those 'lucky' nights of good seeing).

The actual resolution 'limits' of a scope, rise directly with aperture, so though the contrast 'edges' will be slightly degraded by the central obstruction, the larger scopes will (in perfect conditions), be able to see more than smaller units. However there is then a separate 'issue', from the atmosphere. The atmosphere, tends to have 'cells', which result in the shifting, and focus changes seen through a scope, as they move through the field of view. The commonest 'size range' for these, is between about 5" and 8" across. Now a scope that is small enough to look through one 'cell', can then even on quite turbulent nights have the momentary flashes of good seeing. However larger scopes will be looking through several cells at once, and the good moments will not be quite as clear. This is why scopes like 6" refractors, are often felt to be the 'best' planetary scopes, since they give the best resolution for the light path diameter, and this is still small enough to take advantage of a cell when it does happen to line up right. However on those nights when the air is still, a larger scope will resolve more. Some planetary observers, have even deliberately 'stopped down' larger scopes with a mask, to work on the poorer nights. Larger scopes, have the 'downside', of their size (in terms of setup etc.), and with this comes a very much extended cooling interval. Your ETX, will probably be giving good views, within only a few minutes of your starting observing. With a 10" scope, the 'thermal adjustment' time, can be hours (on some nights, the temperature is shifting so much, that the larger scope never 'catches up'. This again degrades the 'perceived' ability of these scopes...

So, at the 'ultimate,' a bigger scope will win, but on a lot of normal occasions, something like a 6" ED refractor, will be easier to handle, and often match the performance of the bigger scope, for planetary views.

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

Subject: Is Lunar Observing Better with Larger Meade SCTs? --part 2

From: Doc G

That it is a "spectacular" reply. Mr Hamlett is very knowledgeable. I always read his replies even when it is not a topic of prime interest to me.

That said, I take issue with one comment. "something like a 6" ED refractor will be easier to handle..." There is nothing "easy" about a 6" refractor. It is large, heavy, clumsy and costly. Not only that, but the eyepiece is often, if not always, in a poor location for viewing.

I would think that an excellent MAK, like the 125 mm, would be very good for viewing bright objects. The Meade ED is not really fully apochromatic. Several other makers do provide fully apochromatic refractors. I would take a 4" TeleVue or Takahashi, or one of many others that are fully apochromatic. For bright objects chromaticism is a very important feature of a telescope. There are even a few super achromatic refractors available, but they get quite expensive.

You have never seen the moon until you look through a TV NP101 with a binocular viewer. Try that sometime.

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

Subject: Is Lunar Observing Better with Larger Meade SCTs? --part 3 of 3  

From: Roger Hamlett

Doc G wrote:
> That said, I take issue with one comment. "something like a 6" ED refractor
> will be easier to handle..." There is nothing "easy" about a 6" refractor.
> It is large, heavy, clumsy and costly. Not only that, but the eyepiece is
> often, if not always, in a poor location for viewing.

Fair comment. It does (of course) depend on the focal length. A friend has a 'short tube' 6" ED scope, and this is pretty easy to handle, but not a Meade scope. I must admit I have an 8" Mak Cass for exactly these reasons (not a Meade scope either).

The Mak though, suffers even worse than the SCT, from cooldown issues (though mine has twin fans, which largely 'solve' this). It has a smaller CO, than the Meade unit, and a faster focal ratio (f/20). With a measured Strehl ratio, over 97%, as a purely 'planetary' scope, it is pretty much unbeatable, since any refractor to match it's aperture, without too much chromatic aberration, would be 'astronomically priced'... So revise the comments, to say that in terms of pure value for money, convenience, and really good views on planets, something like this would 'win'.

> You have never seen the moon until you look through a
> TeleView NP101 with a binocular viewer. Try that sometime.

A good point. The effects of binocular vision, do help the brain to process the images, and even through normal sized binoculars, the appearance of 'form' in the views, especially on some of the surface features, can really be impressive.

As has been mentioned here, planets are particularly 'bad', when the problems of chromatic aberration enter the equation. A pure 'reflector' (Newtonian) scope, does not show CA. However an SCT, will. However relatively little compared to many refractors. The finest 'detail' images I have taken of the moon using an SCT, were actually done using a H-a filter, which noticeably improved the ability to get really 'pinpoint' focus. A Mak (if properly designed), does not show measurable CA. Refractors will show CA, with the designs that bring it down to acceptable levels being the most expensive types. The NP101 mentioned above, is one of the best. I have never tried the combination mentioned, but have tried a binoviewer on a FS102 (which does not have quite such good color correction as the NP101, but gives a slightly larger image scale), and it does give a new meaning to 'seeing'...

Subject: Dressing for Cold Weather Observing--part 1 of 4 

From: Keith

On the subject of keeping ones toes warm in winter... I've discovered that the best way to keep your toes warm is to keep your legs warm. Your legs can take an incredible amount of cold and you won't be aware of how much their enduring until your knees feel it, -- but your toes REALLY are the ones that suffer. No amount of socks will keep your toes warm if the blood is cooled on the way to them. I've found if I wear long johns and something like a snowmobile suit or insulated work suit or equivalent, that you can almost get by with street shoes and ordinary fuzzy socks.

The next most important thing after keeping your legs warm, is wearing clothes and footwear that restricts circulation as little as possible -- almost loose. Make sure everything on your feet is close to being loose. Too many socks or too thick socks that make for a snug fit cut down circulation, and are actually worse than less or thinner socks. If it's really cold, I like dedicated cold weather footwear with the 1/2" insulated felt inserts.

If you really want to get into the fine points, socks that leave marks on your ankles from the elastic are on the verge of too tight. Add to that the elastic from long johns that end up in about the same place on your high ankle, and you've got a circulation restriction that adds up to colder feet sooner if your out there for hours. So does too tight pants over long johns that cause binding in the knees.

My last tricks are concerned with what's between me and what I'm standing on. What your standing on is what comes through to cool the bottoms of your feet. Simply moving around helps here, but not much unless it's steady. By the time you have to move around to get your feet warm -- it's too late. If it's not so cold, and you've just got regular shoes, putting on a simple pair of loose-ish rubber overshoes can help a lot.

Editor's Note: a piece of carpet or an entry mat to stand on can help a lot to keep the cold from coming in thru the bottom of your shoes.

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

Subject: Dressing for Cold Weather Observing --part 2

From: John Oliver

From my experience at the South Pole. Multiple layers, overlapping at transitions are best:

• stand on an insulating mat (old carpet works, too)
• thick, insulating soles on boots (I preferred inflated, air-insulated "Bunny Boots" but perspiration collects and the feet risk bad things if not dried regularly) ... good high top hunting boots will be better
• two pairs of socks, cotton inner, wool outer, but not so thick as to be too constricting
• thermal underwear, tucked into boot top inside outer wool socks
• wool pants, inside boot top but outside outer socks
• outer canvas pants or jump suit gathered around outside of boot tops.
• similar upper wear

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

Subject: Dressing for Cold Weather Observing --part 3

From: Scott Baker <scottb80cts.com>

I bought a pair of the convertible fingerless mittens last year from Wal-Mart, and they were great! But I managed to loose one at an observing site, and it never turned up. I went back to Wal-Mart last week to but replacements, only to find, that they don't carry them anymore. I shopped all around local stores and no one had any. I ended up buying them from the following URL:

   <http://www.harrietcarter.com/>

They're a little more then the $7.95 I paid at Wal-Mart, but this is the cheapest I could find them on the Internet. One thing I'm going to try with this pair is to cut a slit at the joint of the thumbs so that they can be exposed as well. I found that tightening thumb screws with the gloves on, even with bear fingers, just didn't feel secure. And typing on my laptop didn't feel right either. With a slit at the joint of the thumb, I should be able to pull it up and over my thumb, then slip it back in when done (I hope).

Editor' Note: also try the hunting section in sporting goods dept./stores for these fingerless mittens.

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Subject: Dressing for Cold Weather Observing --part 4

From: Mickey McInnis

Be careful with heat packs. Some of them warn that you shouldn't place them directly against the skin due to the potential of burns. This is exacerbated by the fact that when your hands are numb, you may not feel the burning. Also, there's a level of temperature that, if you apply it for a few hours, you'll get a burn without necessarily feeling pain. This is part of the reason a lot of people get really bad burns from electric heating pads.

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

Subject: Dressing for Cold Weather Observing --part 5of 5  

From: Jack Estes <jackesteshotmail.com> Date: Dec 2003

Take a look at Refridgewear: <http://www.refrigiwear.com/>

Subject: Telescope Storage-- Use of Heat Tape for Condensation Control

From: Dave Graham

I would use a product widely used in reptile cages, cat and dog enclosures and the like called Flexwatt heat tape. It is made by CalorIQue. It comes in several widths, in nice rolls with pre-segmented 1-foot sections. The manufacturer's home page is <http://www.calorique.com/>

Flexwatt comes in different widths which determine how many watts you get per foot. This link will take you to a page where everything you might need can be found: <http://www.beanfarm.com/>

If I were to build one, I would just mount the Flexwatt onto a piece of 1/4" plywood with the foil tape, and stand it up on edge so as to get good air circulation, radiation and minimum loss of heat to the floor. Either that or put on top of something like a milk crate if you don't want it standing on edge. I might go for a thermostat in line, but would pass on the dimmer as overkill.

Subject: Green Laser Pointer Selection Advice

From: Todd Hargis

Todd Hargis, who frequents the TSP every year (gave a sketching talk last year) and is a collector and expert of laser pointers. He advised (see quote following) that the DeHarpporte stocked pointer is not a quality product, in his opinion. See: DeHarpporte Trading Co., link:

<http://store.yahoo.com/deharpport/jk.html>

Todd Hargis wrote:
About the DeHarpporte laser pointer, you can only buy that one from the dealers listed on their web page. I have that exact laser and to be honest they are not that great. I have sent one back to the company, twice, and still did not get a good one. I ended up getting a refund.

The best green laser on the market right now costs $119 + S&H and here is the webpage:
       <http://www.lasersale.com/catalog/display_item.asp?id=1063>
Get the one that is continuous wave not pulsed! Model: HLI 8000CW Green Beam Laser Pointer 532nm

This laser is way brighter than the DeHarpporte! Only comes in silver as opposed to black. And it works best when it is cold! All lasers behave differently though. Some get brighter when warm, others get brighter when it is cold, and some don't change at all. I have been collecting lasers for a long time now, and I know which ones are best. This laser is a very good one!

Subject: Green Laser Caution & Star Party Etiquette Links 

From: Darin Koch

For those of you who are getting a green laser and those who might in the future or for any laser device, please read the following concerning their use and safety.
Other links about how they work/star party etiquette/safety:

<http://www.scopestuff.com/ss_lasr5.htm>
<http://web.princeton.edu/sites/ehs/LabPage/laserpointers.htm>
<http://www.hps.org/hpspublications/articles/laser.html>

Mickey McInnis wrote: Even if you do point a legal laser pointer into someone's eyes, it won't cause a detached retina. If anything, it will cause a "burned" spot on the retina. This would be a (probably temporary) blind spot, like the after image from staring into any bright light. In severe cases, it would be a permanent scarred spot. They actually use medical lasers to cause burned spots on the retina as treatment for detached retinas. It "welds" the retina back to the eyeball.

Permanent eye damage with legal laser pointers is very difficult to do accidentally. Looking through a telescope doesn't really make the problem any worse.

However, be careful and don't do it anyway. It's an unpleasant experience. You might also cause some physical injuries if the person jumps in reaction. At the very least, they'll experience the same kind of temporary blindness that a flashbulb will cause. They might also react and cause physical injuries to your or your laser pointer. 8-)

You might do eye damage if you deliberately stare into a laser pointer. Even that is iffy.

The following article was written by "the Department of Ophthalmology, Mayo Clinic, Mayo Foundation, and Mayo Medical School, Rochester, Minn." It was reported in the AMA's "Archives of Ophthalmology." Vol. 118 No. 12, December 2000.

Don't read further if medical details bother you.
   <http://archopht.ama-assn.org/cgi/content/short/118/12/1686>

My summary: Patients stared directly at a laser pointer for 60 seconds in the "fovea" (center of vision) for 1 minute, 5 degrees off for 5 or 15 minutes. No obvious permanent damage occurred.

These were 3 volunteers with medical conditions that required removal of the eye in question. The patients were examined after the exposure and the eye was removed weeks later and examined. The patients reported short term afterimage effects. Nothing major was reported in the discussion.

And to say it again anyway, despite the low risk of injury: Never point a laser pointer at someone's eye deliberately, or stare into the beam.

Subject: Green Vs. Red Lasers

From: Bill Keicher <wekeichercomcast.net>

I have a number of red laser pointers and one green laser pointer ($60 on E-bay including shipping). The red laser is based on a simple semiconductor laser diode an a regulator and is similar to the diodes in DVD players (650 nm). This is why it is cheap. The green laser is a much more sophisticated system. It uses a high power (~1 watt cw) infrared semiconductor laser operating at 808 nm that is used to pump a Neodymium doped, Yttrium OrthoVanadate (a doped crystal) solid state laser which then lases at 1064 nm (infrared). The solid state laser is polarized and is used to optically pump a crystal of Potassium Titanyl Phosphate (KTP). The KTP crystal is use to frequency double the 1064 nm signal to a 5 mW 532 nm (green). The light is polarized and of very high spatial quality (close to diffraction limited). The laser pointer has focusing optics, a filter to block the 808 nm and 1064 nm infrared signals and, of course, a DC regulator. This laser eats batteries and if used continuously, overheats and the optical power drops.

Some models are pulsed so that the maximum duty cycle is 50%. This miracle of electro optics is amazing and it is packaged and sold for only ~$60! I bought it because it not only is a cool pointer (very bright - near the peak of your eye's sensitivity, and not really capable of burning your retina - i.e., no permanent eye damage) but an incredible electro optic system. Did I need it? No. Do I like it? YES! How do I use it? - As a laser pointer, of course. It's fun to explain how it works to other engineers and physicists. There are web sites that show a disassembled green laser.

Caution: recently an amateur astronomer who has a federal indictment against him because of pointing a green laser at an airplane. He claimed he was showing his son the sky.

Subject: Chart Illuminator Recommendation  

From: Dennis Hardy

Well it arrived on Saturday in the mail. Since the weather here was not the best for observing and I was anxious to try it out, so I took it and my star charts down into the basement to give it a try. It works great. Not too bright that it annoys you, but bright enough to light up the charts.

For those that are not sure what I am talking about here is a brief summary. I found a chart illuminator that pilots use when they are flying at night. It comes in your choice of white light or red. They both use 2 LEDs and run on 4-AAAs. It is made of a sheet of acrylic that measures 5 1/4" x 8 3/4". The over all size is 6 3/4" x 9 1/4". On the edge is a black plastic housing that holds the batteries and a small push button that allows you to turn it on to two different brightness levels on also off. The batteries are supposed to last around 40 hrs. It comes in its own foam padded box that looks like a book, very cool.

When in use I turn it on to the highest brightness level and set it on the area of the charts that I intend to use. No need to hold it like a flashlight. It illuminates a large enough area that you need not move it very often. I messed around with it for about 15 minutes and found that I could even use it on the lower brightness level after my eyes adapted to the darkness. I figure the batteries might last longer on the lower setting.

If anyone is interested in getting one go to Sportys Pilot Shop. Their web address is: <www.sportys.com> The part number is: 7828A. The cost is a little high I think, $44.95, but now that I have it in my hands I think it is money well spent.

Subject: Red Light Bulb Paint for Star Parties  

From: Jack Estes <jackesteshotmail.com>

I have for years been using a red film doubled up over my light fixtures. This has worked okay but the film eventually melts over the incandescent bulbs.

I've found a paint made by Dupli-Color that is an engine enamel spray on paint rated for 500 degrees. I've tested two bulbs in their Ford Red DE1605 paint and it looks as though this is the solution I've been looking for.

Though the bulb after painting looks as though it's not translucent it is in fact the perfect luminosity and color. I've found the product at K-Mart and Pep Boys auto parts.

Subject: Testing for Diagonal Positioning Error Caused by Rotation

From: Eugene Lanning <ealannialltel.net> Date: May 2003

Goal of the test:
To quantify the positioning error that results from rotating a standard 1.25" Meade diagonal in the eyepiece holder.
    Download the PDF here.

Subject: "FAKE" Lumicon Filters?   

From: Ed Isenberg <Public1isenberg-family.net> Date: May 2005

Folks, I have just spoken again with "Mike," who identifies himself as the General Manager of Lumicon International. Here is what he has to say. Much of the following has been reported elsewhere.

1) Lumicon INC. used to be based in Livermore. Lumicon INTERNATIONAL is based in Simi Valley, and is a company purchased by Park. This change happened in 2002, some three years ago.

2) Certainly in the last three years, and probably for as many as 10-20 years ago, Lumicon engraved at least their name and possibly the filter type (e.g., O-III) in the filter ring. Before that time, possibly 10-15 years or even longer, they may either have had no label or just a "paper label" that could have been worn away.

3) With excellent care, Lumicon filters should last a lifetime. However, if an owner has washed the filter with unknown chemicals, or wiped a dirty filter with a cloth (where the filter could have been abraded), or under other quite-possible circumstances, then the filter quality could have been degraded substantially. This is particularly important for H-alpha filters, where "pinhole" or other impurities or problems could result in damage one's telescope or even worse one's eye.

4) Lumicon INC. (the older Livermore company) may also have sold good-quality "seconds" and cosmetically blemished filters new without any brand name being inscribed. That is NOT true with Lumicon INTERNATIONAL, which only sells filters designed for astronomical use and that have been manufactured by them to the highest tolerances.

5) Lumicon INTERNATIONAL argues that the quality and/or longevity of their filters may surpass those of Lumico INCORPORATED, due to technological improvements.

6) THEREFORE, those of you with "Lumicon" filters identified only with paper labels or no labels at all will have (a) been sold good if old filters, or (b) may have been sold filters manufacturer by Lumicon but that were "seconds," cosmetically blemished, or manufactured by unknown parties and resold by Lumicon. The current quality of these filters cannot be determined, and could be anywhere from absolutely excellent to very poor (either through deterioration or poor quality control right from the beginning). Lumicon INTERNATIONAL does not stand by these older filters.

6) FINALLY, filters bought from Lumicon INTERNATIONAL since sometime in 2002 WILL DEFINITELY HAVE THE BRAND NAME ETCHED IN THE FILTER RING.

As a personal note, I might add my apologies for any confusion or worry people may have gotten. I worked off of what Mike had told me at the time, rather than what I learned from him just this morning. Should you wish to buy a new Lumicon filter, you probably should double-check that it is engraved with the word "Lumicon" on it. OTOH, if you plan on buying a used filter, you might want to restrict your search to those that have been etched with the brand name on the metal ring (thus showing it is in fact a new filter) and also to insure oneself that the filter has been well taken care of.