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I had the mirror made by one vendor and tested with an interferometer by another This independent testing led to the return of the first mirror for a refund. I then had the mirror fabricated by a different mirror maker (Steve Swayze) with these results.
The process of having a mirror fabricated and then rejecting it took quite a lot longer than I had planned, but the wait was well worth it. The mirror from Swayze Optical is excellent. Maybe better than that. Below are the interferometer test results.
Residual Wavefront Variations Over Uniform Grid (in waves)
Number of points 2970
P-V .199 (1/5 wave)
RMS P-V .029 (1/34 wave)
Strehl Ratio 0.968
CHOOSING THE f RATIO
Keep in mind:
1. The smaller the f-ratio, the larger the diagonal will need to be to maintain a given 100% image plane.
2. The smaller the f-ratio, the shorter the OTA and the closer the eyepiece is to the ground.
3. The smaller the f-ratio, the shorter the exposure time for imaging.
4. The smaller the f-ratio, the smaller the coma-free image plane and the harder the telescope is to collimate..
5. For a given mirror maker, the larger the f-ratio the better the mirror.
6. For a given mirror maker, the larger the f-ratio the better the mirror. (this probably should be #7 as well)