Quote:
Originally Posted by clive milne
...Even a perfectly constructed OTA (of any configuration) that has a 50% central obstruction is in reality no better than 1/2 wave once you include the effects of diffraction.
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...............Roland does not suggest that a Riccardi-Honders delivers 5 micron images (which it cannot) What he says is that a 12" f3.8 produces an airy disk with a diameter of 5 microns, and that his OTA is diffraction limited over a 60mm field.
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I understand the modulation transfer function to only be a measure of frequency preservation....hence and not sure what you mean by saying a 50% obstructed telescope is like having a telescope with 1/2 wave of spherical error... hence.... I still don't agree with your analysis
That much spherical error looks bad visually and easily shows up in images. (I've had some clunkers in my time )
You are indeed correct about Roland's spec claims... but I did some extra research prior to getting the scope, and the Honders has spot diagrams well within the diffraction limit across a 60mm field (attached)
I'd be interested to see a ray trace of a 1/2 wave spherical error....but so far I've not manage to track any down.