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large mak/newts

Started by opticsguy, 02/09/2007 08:35PM
Posted 02/09/2007 08:35PM Opening Post
I am curious about the performance of larger mak/newts, 12" and up. In a past thread in the refractors forum it was stated the big problem with a large mak/nwet would be cooling of the thick corrector plate. One person with very considerable optical and practicle knowledge stated that the real problem was cooling of the primary mirror.

So, with proper cooling (moving air across the face of the primary mirror to disrupt the heated boundary layer) can a large make/newt perform????

I love my 6" f/6 mak/newt and looking for both aperture And refractor like images.


Posted 02/12/2007 10:39AM #1
I used a 14" Mak-Newt which had zero cooling problems, even though it had both thick corrector and fairly thick mirror. In fact, it was cooled down and ready to go as soon as the sun set and had none of the thermal plumes and swirling that I saw in a 16" Dob at a friend's observatory.

Having made Maks up to 10" myself, and used a 14" Mak-Newt with Russian optics, with none of the dreaded cooldown problems, I believe that most of these problems stem from the way the tube assemblies are constructed, not from the basic optical design. The corrector itself is basically a zero power window, so no amount of thermal distortion will affect the wavefront to any significant degree. I have actually taken a warm corrector from an 8" Mak out to the scope, which was at freezing temperature, placed it on the front of the scope, and measured the amount of correction change. Except for an initial 5-10 minute thermal plume, there was no change in the optical figure of the telescope.

Posted 02/28/2007 09:11AM | Edited 02/28/2007 09:26AM #2
Reading this thread a week ago reminded me of a visit to the Grubb-Parsons works in Newcastle ( UK ) in the late seventies and a group of us being shown around by the late David Sinden to see the wonders that were then being made there, amongst which was the 150" IR thin mirror for Hawaii, the Isaac Newton mirror, another 100" for somewhere I've forgotten and the newly cemented 48" achromatic Schmidt corrector plate for Siding Springs in Oz, ( ...a world first I seem to recall ) and this one presented here ; a 50" Maksutov Corrector plate. ( it says on the caption to the slide of the picture I took at the time )
When I came across this slide again for the first time in thirty some years ( ..was it? ) a few weeks ago, I was at first sceptical that any Mak. had ever been made that large but on scanning it into the computer a few weeks ago, and looking at it again now, I see that it must be about right as the brickwork to the rear looks to be right for that scale. An English brick being 9"x3" on the face.
I came across this picture again today and thought some of you might be interested. It's not good I know: hand held available light and not very fast colour film of the time.
I now wonder where it went to ?


Attached Image:

Bruce Mills's attachment for post 112015