Optical Testing

[mick pinner]

does anyone know what it costs to have a mirror tested and an appraisal of it's optical quality.

[matt]

No. Sorry, Mick.

But I reckon it's something which should be more readily available.

Maybe it is, but I'm unaware of anyone offering such a service.

[jase (Jason)]

At this point, I'm only aware of Deep Sky Optics - http://deepsky.cia.com.au/optics/

There are numerous optical tests that can be performed, each with increasing complexity requiring specialised equipment. Its depends on what type of information on your mirror you are after.

[skies2clear]

Originally Posted by jase

At this point, I'm only aware of Deep Sky Optics - http://deepsky.cia.com.au/optics/

Mark from Deep Sky Optics can do this, but depending on what type of report/test you want. If you want to know how good (or bad) your mirror is, the types of aberrations (turned edge, spherical aberation, astigmatism, polish, etc, then DSO can do this, but as far as I know, will not give you an interferometric report, even though he has the expertise. Best to discuss directly with Mark from DSO. Speaking from my own experience, he definitely knows what he is doing and is one of the best around, and has not only tested one of my mirrors, but refigured it to perfection.
Of course, for this kind of support, there will be a fee.

Clear skies,
Nick

[bojan]

Why don't you have a look at some ATM site and do it yourself?
It is quite easy thing to do (to determine your mirror is bad I mean) by using a point light source and edge (Fucault test, easy and widely used).
And of course, visual test on bright star (with good eyepiece) or difficult double should be enough to satisfy your first levels of curiosity.....
These tests, performed by others are not cheap, to do them may cost you more than new mirror (from GSO)

[Geoff45 (Geoff)]

Originally Posted by bojan

Why don't you have a look at some ATM site and do it yourself?
It is quite easy thing to do (to determine your mirror is bad I mean) by using a point light source and edge (Fucault test, easy and widely used).
And of course, visual test on bright star (with good eyepiece) or difficult double should be enough to satisfy your first levels of curiosity.....
These tests, performed by others are not cheap, to do them may cost you more than new mirror (from GSO)

Yes, it's quite easy to check if the mirror is bad--turned edge, rough surface, zones etc. However, with focal ratios of f5 and faster, testing to see if the mirror is good (ie how close the mirror is to a perfect paraboloid) is quite tricky if you haven't ever done it before. The star test is probably your best bet. See "Star Testing Astronomical Telescopes" by H R Suiter. Bintel sell it for $69--it's well worth the price.
Geoff

[allan gould]

Originally Posted by ghsmith45

Yes, it's quite easy to check if the mirror is bad--turned edge, rough surface, zones etc. However, with focal ratios of f5 and faster, testing to see if the mirror is good (ie how close the mirror is to a perfect paraboloid) is quite tricky if you haven't ever done it before. The star test is probably your best bet. See "Star Testing Astronomical Telescopes" by H R Suiter. Bintel sell it for $69--it's well worth the price.
Geoff

Getting Suiter's book is excellent advice. Using it I was able in about 10 min to show that an apo refractor I had sent to me was below par with undercorrection as well as astigmatism. Scope replaced with one that was near perfect. Easy to see once you know the signs (and you buy from a good retailer).

[Satchmo]

Originally Posted by bojan

These tests, performed by others are not cheap, to do them may cost you more than new mirror (from GSO)

Bojan

I don't know how cheap GSO mirrors have gotten these days, but I've always charged $100 for a full test including quantitative measure of spherical aberration and any features that may depart from Diffraction Limited quality. Funnily enough ,while most people would like to know how good their mirrors are few have ever paid to have their mirrors measured.