Posts Made By: Walter Hamler

Floyd, where are you getting them coated?

Walt

Are they making one for the older C-8 as well? I just took a rubber washer, 1.5" od with a 1/2" hole in it that I pushed over the existing C-8 knob. It actually works pretty good.

Walt

There is a member of our astronomy club who has a Celestron version of the Sky View Pro with an 8" f/5 ota that he does some pretty good astrophoto's with on film and digital. Other members have the LXD55 and the 10" f/4 SN, but I haven't seen any actual results from their attempts. I like the looks and feel of the Celestron much better myself.

Walt

Before you "fix" it, make sure it is "broke". Actually, every Meade 16" that I have viewed through gave some pretty good images. Do a simple star test first, because a turned edge is easy to spot when you know what to look for. Also, get a ronchi screen, about 100 lpi, and check on a star again. I can't easily describe what you need to look for here, but there are plenty of web assets out there that will give nice pictures of what to look for. Others may chime in as well and some may know some exact links to go to. Also, the ultimate test is your views to date. How satisfied have you been with the views the scope has given? Unless you have some concrete complaints, I doubt that you have a bad mirror. The problem is with the larger mirrors is that the sky conditions rarely allow any scope larger than 10" to really "strut its stuff".
Once you are able to make some quantitative tests you will be in a better position to decide where to go from there.

Walt

Joe, there is a surplus type store here in Orlando that has a limited supply of Teflon pads, approx 1" x 2.5" x 1/8" thick. 0.50 each. If you want me to pick some up let me know.
They already have been drilled and countersunk at the ends for screws to attach to a surface.

Walt

As Rick has pointed out, NEWT will give you all the possibilities as you plug in the numbers.
Back in the 70's and 80's when I used to do a lot of film astrophotography. I used an 8" f/5 that I custom built for photography. It had a 2.14" scondary that gave about 75% illumination over a 35mm frame. In all honesty, I could barely see the falloff at the extreme corners, and if I cropped any at all, which was usual, there was no problem. A few years after building the scope I tries a 1.83 diagonal for some visual use, and ended up taking some photo's one night with the smaller diagonal. I could barely tell the difference.
The truth is that even very expensive camera lenses do not fully 100% cover the film plane at wide open aperture. I tend to think that we sometimes overrate the "fully illuminated fov" issue.

Walt

Adam, the RA drive you have is most likely driven by an ac synchronous motor. They are good motors but unfortunately the telescope industry has made several iterations since that drive was new. Now stepper motors and even newer, servo motors, are most commonly used. They both run on DC voltage. Changing your motor over to one of these is possible but I wouldn't recommend it unless as a last resort.
There used to be commonly available drive correctors that would change 12dc into 110vac with a variable frequency output. The variable frequency would allow minute changes in the speed of the ra motor to make corrections for drive errors when doing astrophotography. However, no synchronous motor can be sped up enough to allow a goto type operation. That is why most have gone to servo motors because the speed range available is very great.
First you have to ask yourself why you want to have the variable speed capability. If for photography purposes, Astromart frequently has older drive correctors like I mentioned available. As a matter of fact, one was just listed a few days ago and may still be available. As for the declination axis, if there is a manual slow motion system there you can simply add a 12vdc slow speed motor, maybe 1 rpm, to that and the controller mentioned usually has an output for the dec axis that allows you to run that type motor.
Once you get a system like that going you would be good for some piggyback wide field type astrophotography, which is a great place to start. Once you master that, you are well on your way to wanting bigger and better, which is where we all end up sooner or later!
Welcome to the world of amateur astronomy!

Walt

Depends. If you are in a temperate climate with mederate temperature swings the plate will probably be fine. If the conditions are more harsh maybe pyrex would be better. I say "maybe" because the tube current problems would most likely be more prominent than any expansion/contraction factors in the glass.
I live in FL and have made several mirrors, both pyrex and plate, and have never had a problem with either that was temperature difference related. I have found that plate is faster to polish but a pyrex polish is superior. Also, plate is much easier to scratch than pyrex.
Hope this helps.

Walt

I concur. Floyd. The differences are so minimal that it's not really worth it.
Your description of the mirror surface is interesting. I just had a friend bring a mirror to me that I made about 5 years ago. It looked similiar to what you describe. I put the mirror in a solution of Circuit Board Etc from Radio Shack and the coating started coming off almost immediately. Usually it takes an hour or so to see it starting to work. Something was wrong with the coating for sure.

Walt

Here is my attempt this noon. 6" f/6.7 newt, Coolpix and 18mm ep.

Walt