Quote:
Originally Posted by Satchmo
I did ray traces once that showed perfected optics with a 45% obstruction producced an EER ( Strehl taking into account the obstruction ) of 0.72 and system with 1/4 wave spherical aberration of 0.8 ended up at EER of 0.68 obstructed.
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To calarify :
The Strehl ratio is the proportion of possible light into the the Airy disc that
optics can deliver. In broad terms an unobstructed system can theoretically deliver 1.0 and a system with 1/4 wave P-V of pure spherical aberration delivers 80% into the disc and 20 % scattered into the rings.
My example of the 45% obstructed instrument was to show that a system with `perfect' optics and a Strehl ratio indicating a full 20% more light intensity into the centre of the airy disc ( compared to the the 1/4 wave system ) only achieves a real gain of 5% when the large obstruction is taken into account. In other words it's really a case of diminishing returns seeking perfection in a heavily obstructed instrument..
Hope this is not too arousing
Mark