[Wavytone]

Good point Logan, and it has me scratching my head as to what was actually measured/calculated.

P-V 1/8.8 does not correlate with Strehl 0.993, no way, something wrong there IMHO. Also “surface error” is meaningless (a refractor objective has 4, 6 or more surfaces) - wavefront is what it’s really measuring - which suggests the software was written for testing mirrors - in which case the wavefront error is exactly double the “surface error” plotted on the graph at the bottom. If that’s the case the P-V wavefront error is more like 1/4 and RNS 1/10, which are still both entirely respectable.

Conversely when testing lenses the refractive index matters when calculating surface errors ... but then the P-V value is way off for the contours shown.

The contours do suggest the outer 3mm has a turned edge, but whether its worth masking off is another matter (its minor and I would not - aperture counts).

In any case it appears quite good if the measurements are to be believed, and for imaging, anything above 0.93 I'd defy anyone to tell the difference because so much depends on the seeing on the night and other factors such as flatteners, reducers and filters all of which may not be so good - and all of which contribute to the end result at the focal plane. It all comes down to the end result.

Visually you might - and only maybe - spot a difference visually side-by-side with say an AP130GTX on a night with 10/10 seeing.