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Posts Made By: Keith Lawson

November 20, 2004 03:46 AM Forum: Refractors

Is B58-53 problem glass?

Posted By Keith Lawson

Here is a screen capture shot of the performance of a corrector I worked on using Corning B58-53 glass (yes, I know others have been down this road). The attached file shows the on axis performance. Screen 1 in the picture shows the final color spots to be well within the airy disk. I have other examples if anyone is interested. Coor2.jpg will show the on axis performance with the corrector knocked out of alignment. The corrector is tilted 1/2 degree and is moved off the axis by almost a 1/4 of an inch. All the color spots are still within the airy disk. Coor3.jpg will show the on axis performance at the edge of a 1/2 degree field of view. It's still almost diffraction limited at this extent. The curves on the corrector are gentle and it's a oiled triplet. The primary objective (203mm F/15) is designed as an oiled doublet using common glass. The corrector is only 85mm in diameter. I've run the design through another optics program and I get the same result. Can anyone tell me what the problem is with this approach? Is Corning B58-53 a problem? Price, availiability, etc. I can post the other files if anyone is interested.

December 2, 2004 10:33 PM Forum: Pictures of Me and My Telescope and........

Active Cooled C9

Posted By Keith Lawson

Hi All,

This is what happens when you are a planetary observer/machinist and can't afford a "High End" apochromatic refractor. Here is an active cooled C9 on a modified Meade fork mount. The fork mount has been converted to a GEM (rock solid). The C9 has a closed loop (sealed) cooling system and a modified secondary holder (reduced from 36.5 to 32.4%). I completed it in the summer of 2001. Did all the mods make an already good scope a better performer? Oh yeah!

December 3, 2004 10:42 PM Forum: Refractors

Re: Jaegers Optics

Posted By Keith Lawson

Ouch! Those prices! Some of us have been around long enough to remember that the bulk of the sales for Edmund Scientific and Jeagers were to amateur astronomers and telescope makers. It seems like once the "sons" took over the prices changed by quite a bit.

December 18, 2004 11:49 PM Forum: Pictures of Me and My Telescope and........

Active Cooled C8

Posted By Keith Lawson

Just finished my mods on a C8 OTA. The active cooling system (closed loop) really helps clear up the images. This combined with pin-point collimation helps to make the scope perform to it's optical limit. I would compare it to a 6" Apo on planetary performance (contrast) with brighter images of course. High power star images show the classic airy disk with a single diffraction ring. The dew shield is a custom machined tube with machined grooves inside for a truly flat black internal surface. I don't like those "wrap around" types. I wanted it to look like it was part of the scope like refractors. Lotta work? Yep! Worth it? I think so. Hope to demo it at RTMC 2005.

March 27, 2005 04:40 AM Forum: Celestron

Did it again (Cooled C-11)

Posted By Keith Lawson

After good success with my C-8 I decided to do a C-11. Currently observing Saturn through the sucker holes in the high clouds. It's amazing what you can see through a large, well collimated and cooled SCT. Crisp, well defined detail. Easily as good as some of the best CCD image of Saturn Ive seen. WOW! High end apo refractors are nice but if I can get the same performance without breaking the bank or my back well......

April 15, 2005 05:00 AM Forum: Solar System Observing

GRS Disturbances

Posted By Keith Lawson

Anyone looking at or photographing the large disturbances next to the GRS on Jupiter?

May 8, 2005 03:30 AM Forum: Refractors

Refractor on a Stick (Lens testing)

Posted By Keith Lawson

This is for all the "pristeen" refractor owners. Yes, it works quite well. Only two baffles? Yep, but well placed though. Getting a good view of Saturn right now and I'm going to Jupiter next. The lens tests out quite well so far. It's a 6" F/8 from Antares in Canada. Just having fun grin

June 14, 2005 10:46 PM Forum: Equipment Talk

One For Roland Christen

Posted By Keith Lawson

I don't know if this has been asked of you before but, if you were an "average" amateur astronomer like the rest of us and didn't have access to an interferometer, what would you use to test compound instruments for optical quality? I know that some don't care but I like to know the optical quality of my instruments. I have read and re-read your "essays" at: many times and love the detailed info on telescope performance ( your CCD/MAK photos are flat incredible!) but what can the "average" amateur telescope owner do to know his or her optical quality?

At present I use a 250 line glass grating inside focus showing 4 bands and the out of focus star test to test my instruments. I use the airy disk (when seeing allows)as my final test. It's all I got smile

September 1, 2005 01:52 AM Forum: Pictures of Me and My Telescope and........

Re: Ugliest Scope Contest!

Posted By Keith Lawson

Ok, I figured I would throw in my "refractor on a stick". This was a fully functional 6" F/8 refractor. After testing the lens I installed it in a Meade AR6 OTA to replace a bad lens that came with the OTA.

September 6, 2005 03:22 AM Forum: Refractors

Magic Glass (8inch F/7 Simi-Apo)

Posted By Keith Lawson

This is for the lens designers out there. Just something to play with. The design uses all common glasses except for one. Can anyone tell me if the "magic glass" can be made? If not, why? Just trying to learn something so please don't flame me 8) BTW, the design at F/9 is an APO. If anyone is interested I will post the data.