Under or Overcorrection via Interferogram?

Hi All,

I'm shopping for a refractor objective for an ATM project. The company rep said that he could let me have the interferograms of the objectives that he has in stock. Is there any way that the interferograms could be used to determine whether the objective is under or overcorrected? Also, can these interferograms be used to determine how much astigmatism (if any) is present in the objectives? Thank you.

Anjal.

Yes all these parameters can be easily determined. Usually the interferogram will already have been processed through some software, and the quantities will be listed in thr report. In addition, an overall quality rating called the "Strehl ratio" will be listed, and the closer this is to 1.00 the better the lens. Strehl ratios values above 0.96 generally indicate a high-quality lens.

If you have only the raw interferogram image to look at, in general you want to look for very straight, evenly spaced, lines (often called fringes) in the interferogram.

There are many examples of interferograms and their interpretation in Wolfgang Rohr's postings at this website. Here are a few quick examples. You can learn a lot by perusing his postings. Here are links to just a few on refractors:

http://www.astro-foren.de/showthread.php?12497-Sechs-reisetaugliche-Refraktoren

http://www.astro-foren.de/showthread.php?11530-Vixen-ED-APO-115-S-F-890

http://www.astro-foren.de/showthread.php?11436-Takahashi-TSA-120-900

http://www.astro-foren.de/showthread.php?10123-LOMO-Triplett-80-600

http://www.astro-foren.de/showthread.php?11698-Lzos-apo-115-805-354