Antares Zygo report

[neil phillips]

Hi guys i ordered a 1/30th Antares secondary.  For my 10" Orion F6.3 Now installed, Dont really understand the numbers on this. Any experts out there, that do understand these zygo reports.
Interested what they make of these numbers. Cheers for any insights

Edited March 29, 2021 by neil phillips

[neil phillips]

Well after 28 views all i can say is me neither ha ha.

Though i will say the oblique plot looks very flat. as does the surface wavefront profile. Better than a few other  Antares zygo reports i looked at on google.

Edited March 29, 2021 by neil phillips

[Roy Challen]

Well, I use a zygo all the time at work. However, we analyse surface roughness (not the same as wavefront error but probably related) of metals, step heights, form etc. The line across the top left image is being analysed in the plot below it. However, I don't know what the analysis is looking for, so can't tell you what the numbers mean. No units either. This is from an old zygo, maybe Newview 7000, has a resolution of about 0.1 nm (for roughness).

Comparing the images to our old zygo, it certainly seems that the mirror is smooth. But we'd expect that - it's easy to make glass smooth.

Sorry I can't be of more help!

[neil phillips]

F

27 minutes ago, Roy Challen said:

Well, I use a zygo all the time at work. However, we analyse surface roughness (not the same as wavefront error but probably related) of metals, step heights, form etc. The line across the top left image is being analysed in the plot below it. However, I don't know what the analysis is looking for, so can't tell you what the numbers mean. No units either. This is from an old zygo, maybe Newview 7000, has a resolution of about 0.1 nm (for roughness).

Comparing the images to our old zygo, it certainly seems that the mirror is smooth. But we'd expect that - it's easy to make glass smooth.

Sorry I can't be of more help!

Hi Roy thanks for that. On CN they seem to be concurring that it is around 1/26th pv wavefront

Here is a qoute

I read it as 0.038 wave error, ie 1/26 PV Wavefront over the whole surface. Not using the very edge quickly brings it in much better than 1/30th.

Edited March 29, 2021 by neil phillips

[vlaiv]

Not sure what 1/30th wave refers to (surface or wavefront) - but your reflected wavefront is 1/26th PV wave which makes surface quality twice that - with flat mirror reflected wave will have twice difference between peak and valley - since light travels that distance twice - once on the way "in" and once on the way "out".

You can see that from top left diagram where it says PV 0.038 and reciprocal of that is ~26.32, so it is 1/26.32 PV wave. Paper does not say what wavelength of light was used for measurement, so I would assume above 600nm.

Surface roughness in nanometers depends on wavelength of light as one wave can be 600nm or 400nm - depending on light used to measure (and it is customary to include that in report).

[Adam J]

Basically its a fantastic mirror and you will never tell the difference between this and perfect. 

[neil phillips]

Ok cheers for the input much appreciated. Hopefully soon i can see what the cleaned and recollimated scope can do with it. Antares have a great reputation for thier  secondarys. So hopefully the old beast will perform well. Will be a while before first light. But hopefully not too long. 

Edited March 29, 2021 by neil phillips

[jetstream]

My 24" has an Antares secondary and is excellent.

[jetstream]

Btw, whats just as important as the secondary specs is what is holding it in place...

[neil phillips]

Hi Jetstream. The spider and secondary holder are robust. Never had a problem with it. Got my bobs type knobs from ebay. For a fiver. We will see how they go

Edited March 30, 2021 by neil phillips

[Astrobits]

It is generally recommended that surface analysis is done with several complete interference bands across the surface. If the analysis is done on the image shown in the report then it is not following best practice. There might be a good reason for this and there is no suggestion that the results would be any different if more bands were shown and/or used.

The report could also be a bit more informative with regard to the actual measurements. Two sections are headed "Surface/Wavefront" and as Vlaiv points out, one is twice that of the other, so what is being shown/claimed?

Nigel

[Adam J]

4 minutes ago, Astrobits said:

It is generally recommended that surface analysis is done with several complete interference bands across the surface. If the analysis is done on the image shown in the report then it is not following best practice. There might be a good reason for this and there is no suggestion that the results would be any different if more bands were shown and/or used.

The report could also be a bit more informative with regard to the actual measurements. Two sections are headed "Surface/Wavefront" and as Vlaiv points out, one is twice that of the other, so what is being shown/claimed?

Nigel

Yes I saw that but I did not feel they had cherry picked the band so did not think to long on it. Even if it's 650nm It still seems to be in spec, so again I think it's all great. I don't see anything that would worry me if it was mine. 

[neil phillips]

I will know quite quickly how it performs. I have a good feeling about how the old beast will pan out. Stay tuned.