Re[2]: ATM Airy disk frustrations

[Dwight Elvey <elvey@hal.com>]

SHANE LAPIERRE <SLAPIERR@bcbsct.com> wrote:
> 
> Does this mean there is no airy disk if there is no tube?  Does the shape of
> the mirror contribute to diffraction?

The light limiting obstruction is what causes the diffraction.
In the case of a refractor, it is the lens cell. In the
case of a reflector, it is usually the edge of the mirror.
In a Schmidt camera it is the opening at the front.
Diffraction from things out side of the light path
are there but usually so dim that they are not considered.
The edge of the mirror is a limiting in the same way as
the limiting of a mask in front of the mirror. This was
something that was discussed in an earlier thread.
 Now an infinite mirror, would have no edge. It would
produce an infinitely small disk or an impulse spot.
Well in reality, we should be able to measure the size
of the stars disk. Something like a f/.000000000001 mirror
would be interesting. Can you imaging the field curvature
at focus for this? I guess there really are practical limits.
Dwight