Hartmann mask and seeing

[sculptor]

Hi, folks,

I use a 3-hole Hartmann mask for precise focus (and often forget to take it off before doing 10 minute exposures, just before it clouds over.)

I dimly recall (many years ago) seeing a Catalyst or Quantum or Beyond 2000 or some such in which an Astronomer discussed using something like a Hartmann mask, but with holes in a clever, assymetrical position, not just to focus, but to somehow improve the seeing.

I think he was doing clever wavefront analysis with a super-computer, but back in the real world, it occurred to me that a Hartmann mask with widely separated holes preserves theoretical resolving power but looks through a smaller sample of air. Looked at Gassendi last night (seeing ghastly), with and without mask. Seemed to be far, far better with the mask.

But just stopping the aperture down (ie using one of the three holes) also seemed to help amazingly. Could not really distinguish between one hole and three.

Any thoughts on masks vs simple stopping down to gain crispness without losing resolution?

[sheeny (Al)]

Interesting question. Looking forward to the responses.

If it hasn't been done before (surely it has!) it would be an interesting little experiment to do.

Al.