Opinion on this telescope interferogram?

Hello Everyone,

Just wondering what is your opinion on this 200/800 Newtonian telescope based on the following interferogram images.

Test wavelength: 632.8 nm
Evaluation wavelength: 550.0 nm

RMS: 0.0348
P-V: 0.233
Strehl ratio: 0.953
Astigmatism: 0.039 Axis 11
Coma: 0.0138 Axis 52
SA: -0.0148 P-V -0.0495
Based on 180 points

Why do the intra and extrafocal images show some "squariness"?

Thanks,
Levente

Attached Image:

The numbers imply an excellent f/4 mirror, at the level of 1/8.5 wave
PV of spherical aberration. The squareness most likely results from
pinching by the mirror holder - interferograms show no cause for it whatsoever.

Vlad

Thank you very much for your comments. The top-left image looks as if it were made using a ronchi-grid. In this case the lines should be straight with even spacing, aren't they?

I ran your interferogram through my copy of Quick Fringe. I got slightly different numbers, probably because I ran the fringes right to the edge, including the slight turned edge.

P-V .33
RMS .052 (1/19)
Strehl .90

Interferometric analysis measures everything! If this mirror had been tested through a Foucault, it would probably show 1/10 wave or better.

Steve Dodds

Attached Image: