Quote:
Originally Posted by RickS
Approximately 1.57 times assuming a 50% obstruction by diameter.
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Correct (I got 1.56). And if the 12" has say a 10% larger obstruction (i.e. 55%) then the ratio is 1.48 (ideally).
Cheers, Marcus
PS: my idealized calculation is based on aperture, central obstruction, focal length and pixel size.