Re: ATM Off axis mask

[Richard Schwartz <richas@idt.net>]

-- [ From: Richard Schwartz * EMC.Ver #2.5.02 ] --

> Date: Thursday, 08-May-97 04:16 PM
> From: espector@mlswc.uk.lucent.com \ Internet:   

> I've wondered about this. If one hole is good, because   it avoids the
spider 
> legs and central obstruction, then how about four   holes?
> 
> And then put smaller holes between the bigger holes   etc.
> 
> I eventually concluded that the resulting image would   be diffraction-
limited by
> the smallest hole. 
> 
> Note: I haven't proved this, but I'd expect to see the   large Airey disc
due to
> the small aperture, but with the brightness of a large   aperture.
> 


Behold! I have performed a though experiment!  I start with an off-aperture
mask.  I then add holes to it, between the spider vanes, to produce four
large holes.  I then add smaller holes between those.  I then add smaller
and smaller holes... until nothing is left!  The result is the same as no
mask.

I have performed a second thought experiment!   If an off-center mask works,
I add a second off-center mask in front of it to increase the improvement. 
I keep adding more off-center masks, with smaller and smaller apertures,
until the entire telescope is blocked off.  At this point, the optical
performance is beyond belief; it is equivalent to the performance of a
PERFECT unobstructed mirror or lens with all aberrations ZERO!

Should the fan blow, or suck?