Unless the binary is very tight, I don't see how diffraction will throw
light outside the secondary star--even mostly outside the secondary star.

I was thinking about it and I realize my first answer was rather silly
actually. If I understand it correctly, the Airy disk is ALL diffraction
pattern. After all a star is a point source, so strictly speaking its image is
completely obliterated by diffraction. We have just come to accept that this is
what a star looks like in a telescope, and we aren't particularly looking for
low contrast details on stars, are we?

The effects of diffraction on an extended image, while not as catastrophic as
those on a star image, still blur lines where light and dark meet, smearing
detail. For this reason, I am more "bothered" by diffraction on extended
objects than on point sources, even though it is obviously the star that gets
the real short end of the stick when it comes to diffraction.


I suspect the main reason why higher powers seem tolerable on binary
stars (and lunar observing) is because the input contrast is so high.
Even when you are low on the MTF, the output contrast is still high
enough for your eye to pick up on the detail.


Again, not much detail there. And the other thing is I have a much easier time
looking around floaters in my eye on objects that subtend less than a half arc
sec in total.

In contrast, on DSOs, the contrast is low, so that being low on the
MTF means low output contrast as well. If the object is magnified too
much, the variations in brightness may be too difficult for the eye to
pick out.

DSO's... I wasn't thinking about them. I was thinking mainly about Jupiter.

Another aspect of binary observing that might be relevant is that it is
a relatively well-circumscribed observation. Primary color, primary
brightness, secondary color, secondary brightness, separation, and
position angle. That's about it. Whereas other sorts of observation
are much more varied, and benefit much more from greater contrast.

Yup.

rat
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