Zygo Wavefront Analysis

[magnahrl]

I have an Orion Optics  UK 8" f/6 Newton. It came with a test called Zygotest. There are some numbers I don`t fully understand. Maybe someone can help me?

Strehl 0,982

PV. Wavefront 0.139 wave

rms  0,021 wave

Ast.Mag 0,029 wave

What are those numbers really saying, could be intressting to know....

Test was done Jan 10 2007.

 

Anyway I like this Newtonian. It delivers nice wievs at decent seeing. Startest looks rather good as far as I can judge and  it snaps to focus.

 

Clear Skies!

Magnus A.

[Stuart1971]

Suffice to say those numbers are excellent….👍🏻

Edited April 11 by Stuart1971

[John]

Quite close to the figures that I had for my Orion Optics 12 inch F/5.3 which had Orion Optic's mid-ranking optics. Good optics. Probably a little bit better than the average chinese made primary mirror. 

 

Edited April 11 by John

[Captain Scarlet]

Sounds like a very nice mirror, I have two OO mirrors myself.

Magnus B.

[magnahrl]

Thank you Stuart, John and Magnus for feedback. Very kind! 

Magnus A.

[syd_malicious]

Random question, based on ignorance but something I have pondered.

I too have an OO 'scope with a report. Much is talked about the 1/8th or 1/10th accuracy but surely this doesn't tell the full story? It's a fraction of something and so the wavelength used must, surely, be important too.

My report seems that a red light wavelength is used which must be more forgiving than a green or blue.

That then begs the questions

 

1) what is "normal" for the wavelength used to measure?

2) If most use green or shorted and OO use red then it's a slightly meaningless report to use to compare.

3) What does 1/4 wave (I've read is diffraction limited) in blue translate to in red or what does 1/8th (or 1/10th) in red translate to for other wavelengths?

 

Whilst my mirror seems fine (reported as 1/8th wavew PV) I still have no idea how it compares to others purely based on numbers (and yes I appreciate some answers will be a star test will show things and I don't have the book or the time to analyse using Suiter's book.)

[AstroKeith]

17 minutes ago, syd_malicious said:

Random question, based on ignorance but something I have pondered.

I too have an OO 'scope with a report. Much is talked about the 1/8th or 1/10th accuracy but surely this doesn't tell the full story? It's a fraction of something and so the wavelength used must, surely, be important too.

My report seems that a red light wavelength is used which must be more forgiving than a green or blue.

That then begs the questions

 

1) what is "normal" for the wavelength used to measure?

2) If most use green or shorted and OO use red then it's a slightly meaningless report to use to compare.

3) What does 1/4 wave (I've read is diffraction limited) in blue translate to in red or what does 1/8th (or 1/10th) in red translate to for other wavelengths?

 

Whilst my mirror seems fine (reported as 1/8th wavew PV) I still have no idea how it compares to others purely based on numbers (and yes I appreciate some answers will be a star test will show things and I don't have the book or the time to analyse using Suiter's book.)

Are you sure it's red? I've only ever seen green Zygo tests.

The report should also give strehl, rms and astigmatism figures. 

[syd_malicious]

thought it was, may be wrong. I'll check later.

[davidc135]

Zygo tests are often carried out at both 632 and 532nm as far as I can see. I've never seen one in blue but I expect they could be if it was important for the instrument's use. The p-v rating could be adjusted in proportion if the test was at 632nm so for reflectors it's easy to make an adjustment.

Because modern refractors usually suffer from sphero chromatism ie variation of spherical aberration with wavelength it's more important to know how the objective behaves in green light especially for visual use. I'd be suspicious of one that tested perfectly in red light although there is some tolerance.

Whilst p-v is a handy measure, rms (and Strehl) give a better, weighted, averaged out assessment of the surface. Even then I'm not sure if the Zygo test would pick up roughness, for instance 'record grooves' in the mirror's figure. Maybe it would.

If a mirror has a smooth 1/6th p-v surface, I wonder how many could tell it from one with 1/10th wave optics.

David

[niallk]

I've an OMI mirror, tested at 550nm (green).

Here's their tech note on interferometry results:

https://web.archive.org/web/20080509195633/http://www.opticalmechanics.com/technical_articles/interferometric_testing.html

 

The numbers quoted for your mirror are very good!

Edited April 20 by niallk