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Mirror Evaluation

Started by dan kowall, 09/28/2004 11:35AM
Posted 09/28/2004 11:35AM | Edited 09/28/2004 11:46AM Opening Post
Can someone interpret the attached numbers and image for me?
Dumb it down, please.
Thanks in advance,

dan kowall

Attached Image:

dan  kowall's attachment for post 19048
Posted 09/28/2004 01:01PM #1
Between 1/5 and 1/4 wave peak to valley surface with a RMS of 1/25 wave overall smoothness.
Would be an OK mirror but nothing special.
Defraction Limited
"Diffraction-Limited Optics have a maximum difference between the shortest and longest optical path of 1/4 wave. The root-mean-square deviation is 4-6 times smaller than the total error."
This would be my take on it, let's see what others think.

[SIZE="Large"][/SIZE][COLOR="Blue"][/COLOR] Floyd Blue grin
Amateur Imager
Posted 09/28/2004 01:18PM #2
If the numbers are expressed in wavefront, as Floyd is assuming, it should be okay. The P-V is marginal, but the RMS is actually quite good (which just means that the peak affects a small area of the mirror). If the numbers are surface error, then it is going to be marginal at best (in this case P-V is almost double the diffraction limit, and the RMS is just a bit above the diffraction limit).

But it's kind of a funnly looking picture to me. Does this mirror have a central perforation? It's hard to tell what's going on in the center, there's no sharp edge that I would expect if it was a perforation, but if there is no hole then there is one heck of a mess near the center. Granted, most of it should be in shadow of the secondary most of the time, but still.... I also see a little bit of turned edge both at the outside and near the central whatever-it-is, and the lines on the upper left all have a bend in them. I am not sure that I would believe those number came from this picture if they are supposed to be wavefront.....