Quote:
Originally Posted by clive milne
That is truly an excellent image Peter... I think the point that you have just established is that it is possible to take a world class image with an OTA that has the equivalent of 1/4 wave spherical aberration.
(An RC with a 32% central obstruction has exactly that)
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Well not quite, just because the airy disk energy is, well, not in the disk and has moved to the first ( or more ) diffraction ring doesn't mean the spot sizes will be bloated.
A modulation transfer function only tells part of the story....as does a ray trace which I think has more relevance to deep sky imaging.....
Differences in deep sky images from telescope with a figure error (eg 1/4 spherical) and one with none is obvious....with the latter putting all the energy into a small spot ( albeit larger than the "perfect" airy disk) rather than smearing it over tens of microns due the figure error.
One need look no further than Hubble images pre and post servicing missions to better understand my point....the secondary obstruction remained the same
but the figure and images were sooo much better
