A parabolizing corrector? ..

brian livesey · Post by **brian livesey** » Fri Jan 27, 2012 11:49 am

We've heard of coma correctors for short-focus 'scopes, but is there such a thing as a parabolizing corrector for spherical mirrors?
I'm thinking here of the SKYWATCHER 130/f.7 Newtonian with its spherical primary mirror.

David Frydman · Post by **David Frydman** » Fri Jan 27, 2012 12:11 pm

A Maksutov corrector plate I think.

I will have to think of smaller correctors, there probably are, likely to be Russian.
Also maybe some Finnish, U.S. and British and Dutch.

I will ponder.

Regards, David

A Schmidt Newtonian is probably the best known.
A Schmidt corrector with a spherical primary.

I am pretty sure there are others.

There were Wynne correctors 4 element maybe but I think with parabolic mirrors and maybe Ross correctors also.

David Frydman · Post by **David Frydman** » Fri Jan 27, 2012 12:32 pm

There are numerous photo mirror lens designs. Some are complex. Using spherical main mirrors.
Some with doublet correctors, some with more.
Tamron SP, Sigma 500mm f/4
Russar single and doublet correctors for various MTO lenses. At least three types.
Bouwers

I suppose Brian, you are looking for an add corrector near the eyepiece.

There is a wierd 1000mm and 2000mm movie mirror lens with an adaptor half way down the tube.
I found it never stabilised with temperature and gave awful images, but it is rare, expensive and sought after. Why I don't know.

Regards, David

The whole point is that with the 130mm f/7 scope the performance is adequate.
And if you want something better £20 more will buy you a parabolic mirror scope.
So the whole idea of a corrector here is not cost effective.

David Frydman · Post by **David Frydman** » Fri Jan 27, 2012 12:48 pm

There is a wierd optical device with a fast mirror and sideways eyepiece at the front I think using a spherical mirror and unusual corrector.
I cannot recall whether this was an imaging device or visual, but very decidedly odd.

It is pretty certain if we think of something, most of the ideas will have been done before.

However, John Wall of Coventry keeps coming up with new ideas.
He would probably be the man to ask.
He has just written more of the Hypochromatic refractor.

David

LeoLion · Post by **LeoLion** » Fri Jan 27, 2012 1:47 pm

Have you given thought to a 'warping harness' as a means of flexing a spherical mirror to a paraboloid (or other figure) . There is an article in Sky & Telescope - Nov 2000 by Alan Adler titled- "Flexing Spheres into High-Quality Telescope Mirrors" . There is thread on Cloudy Nights Forum - ATM Section too on the subject. I should have the S & T listed in the bookshelves (in my 30 year + collection) . Let me know by PM if you need a scan of the article.

brian livesey · Post by **brian livesey** » Sat Jan 28, 2012 9:55 am

What I had in mind was a small parabolising lens that can be fitted at the eyepiece end, not a front corrector.
I don't have a spherical mirror, but I wondered if it could be done.

David Frydman · Post by **David Frydman** » Sat Jan 28, 2012 10:02 am

It might be possible but it may need several lens elements.
It would only be cost effective for a large spherical mirror.
For such a small scope as a 130mm f/7 it is cheaper at least for the Chinese to provide a parabolic primary mirror.

Regards, David