Re: [ATM] Tough questions about Aperature Stops

["Paul Bradley" <paul@paul-bradley.com>]

Hi Mike,

I can't answer your first question, and will be interested to see what 
answers come up.

As to the second, you could use any shape aperture stop. The size is 
dictated by how big
you can make it without the spider vanes being inside the aperture. If you 
used something
other than a circle the diffraction pattern (there is diffraction caused by 
both the aperture
stop and the spider/secondary holder) would be something other than the airy 
disk. I seem
to recall circles have the least objectionable diffraction effects, someone 
else will probably
be able to elaborate.

Paul

> 2. Does the shape of the opening in the aperature stop
> matter? Could you use a square for instance? Why not a
> half circle? Could you use more than one opening in
> another place? Why do you use a circle, and why that
> specific size?

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