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Re: p.t.v. error on Discovery mirrors?

Started by Kevin Barker, 11/14/2002 07:19PM
Posted 11/14/2002 07:19PM Opening Post
If you are happy with your telescopes optics perhaps do not worry about the mirror figure. The secondary mirror will also add to the errors in the images as may also your eyepieces.

It must be a reasonably good figure if the views are nice and sharp. To get a near perfect figure will cost a lot more and may not improve images by all that much more.

P-V,etc is quite a complex subject. Also how much of the wavefront is in error and measures of overall average error e.g.(rms)need to be considered when judging an mirror or optics. The main P-V error of part of the mirror may be quite small or the mirror may have a small P-V but quite a bit of surface roughness.

Quoted figures of manufacturers are often the surface accuracy of the main mirror rather than the overall wavefront error leaving the optical system.

Star testing is one way of assessing the optics of a telescope. Suiter's book "Star testing Astronomical Telescopes"is useful here but it is not an easy read. The physics is rather complex. Star testing is not easy to master.

Best wishes

Kevin B