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TerryWood
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Reged: 03/15/12

Loc: Blue Ridge Mountains, USA
Help with Zygo Report
      #6121366 - 10/06/13 09:43 PM Attachment (54 downloads)

Can anyone out there decipher this Zygo Report? I know the mirror is supposed to be good, but the numbers in the attached report have me confused. Any help is greatly appreciated.

I have to send report in 4 parts due to file size limits. Thanks!

Very Respectfully,

Terry


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TerryWood
professor emeritus
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Reged: 03/15/12

Loc: Blue Ridge Mountains, USA
Help with Zygo Report (pt 2) new [Re: TerryWood]
      #6121367 - 10/06/13 09:43 PM Attachment (45 downloads)

Pt 2

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TerryWood
professor emeritus
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Reged: 03/15/12

Loc: Blue Ridge Mountains, USA
Help with Zygo Report (pt 3) new [Re: TerryWood]
      #6121368 - 10/06/13 09:44 PM Attachment (42 downloads)

Pt 3

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TerryWood
professor emeritus
*****

Reged: 03/15/12

Loc: Blue Ridge Mountains, USA
Help with Zygo Report (pt 4) new [Re: TerryWood]
      #6121369 - 10/06/13 09:46 PM Attachment (43 downloads)

Pt 4

Thanks again for any assistance!

V/R

Terry


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ColoHank
Carpal Tunnel
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Reged: 06/07/07

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Re: Help with Zygo Report (pt 4) new [Re: TerryWood]
      #6123725 - 10/07/13 10:24 PM

I'm not familiar in the least with Zygo Reports, my guess is that the various plots show the deviation, measured in wavelengths (probably of green light), of the mirror's surface from some theoretically ideal shape. Those deviations, as shown in the top chart, range from plus 0.03606 wavelength to minus 0.05083 wavelength, for a total wavefront error of 0.08689. That's about 1/12 wave.

The second chart appears to be a greatly exaggerated three-dimensional representation of the same errors (deviations from the ideal) on the mirror's surface.

Again, just guesses on my part, but charts are charts no matter what they're called.


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Les
scholastic sledgehammer
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Reged: 04/22/06

Loc: Maryland
Re: Help with Zygo Report (pt 4) new [Re: ColoHank]
      #6123850 - 10/07/13 11:42 PM

I think Hank got that right. The surface roughness as measured by the rms errors is about 1/71 wave (pretty good). Also shown are various cuts through the mirror showing the wave error (in fractions of wavelength deviation from perfect figure). Lastly is the intensity pattern generated by placing a Ronchi grating in the optical path. Perfect would be straight black and white bars. This test quickly locates places in the mirror where there are large error denoted by curvature of the lines. All in all, a nice example of an anniversary model. I've seen some better rms values but the large areas where you have the peak errors is inflating those rms readings, although 1/12 PV wave error is nothing to sneeze at. My Q50 comes in at 1/10 wave PV but with about the same rms that you show because the worse error occurs over a smaller region confined to the inside end of the donut.

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TerryWood
professor emeritus
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Reged: 03/15/12

Loc: Blue Ridge Mountains, USA
Re: Help with Zygo Report (pt 4) new [Re: Les]
      #6127782 - 10/09/13 08:06 PM

Thanks for the technical information, that eases my mind a bit. It looks like it meets advertised specs so that make me happy. Thanks again!

V/R

Terry


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DAVIDG
Post Laureate
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Reged: 12/02/04

Loc: Hockessin, De
Re: Help with Zygo Report (pt 4) new [Re: TerryWood]
      #6137171 - 10/14/13 02:27 PM

The "bar" pattern is not from a Ronchi grating but by interference fringes. What a Zygo is doing is combinning a known spherical reference wavefront with the one produced by the Questar and the result are interference fringes. The deviation from straightness of the fringes produced is a direct measure of the wavefront error. So 'PV' is Peak to Valley or a measure of highest to lowest wavefront errors which is about 1/12 wave. The 'RMS' is Root Mean Squared or weighted average of wavefront errors, again it is very good at 1/72 waves. The 'Power' is measure of the amount of astigmatism in the system which is about 1/25 wave, again excellent.
Was the test done on the just the mirror or the whole telescope ?

- Dave


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Les
scholastic sledgehammer
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Reged: 04/22/06

Loc: Maryland
Re: Help with Zygo Report (pt 4) new [Re: DAVIDG]
      #6137712 - 10/14/13 07:36 PM

Thanks for straightening that part out for me. It is essentially what is obtained by typical testing with a Ronchi grating while the mirror technician is working the figure to minimize high and low spots.

If it's a 50th anniversary model then it is a report supplied by Questar showing wavefront errors through four surfaces.


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TerryWood
professor emeritus
*****

Reged: 03/15/12

Loc: Blue Ridge Mountains, USA
Re: Help with Zygo Report (pt 4) new [Re: Les]
      #6150283 - 10/21/13 05:34 PM

You guys are wizards, thanks! I think I'll give Jupiter a try tonight. I also have a Daystar filter heading my way. It's being tweaked by Questar right now. Hope to have it back within a month or so. Thanks again!

V/R

Terry


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