(SNES) re: Optical Resolution

[Albireo54@aol.com]

Hi Les,

Thank you for the informative article you placed on the website about optical 
resolution! This is one of those important topics we all discuss in astronomy 
circles, but one about which we seem to have little understanding. 
Conceptualizing what happens within the optical path of a telescope requires 
that we "bone up" on the wave nature of light, and I admit that I'm still a 
bit gray in this area. (Those physics classes were many years ago!)

Your diagram (showing the difference in time for the two beams of light 
emanating from a double star) was very helpful. I drew myself a few practice 
schematics of various sized systems, and it became very clear what happens in 
larger apertures. Rays of light from each star take much different length 
routes in reaching the focal plane. The actual difference in time is obvious 
from the sketches, although measuring this in reality would be quite a task!

I have a good feel for the manner in which light rays strike our eyes, with 
the differing electromagnetic wavelengths creating different reactions on the 
retina - these our mind translates as colors. What is much harder to picture 
is why the [t1 minus t2] time difference, when at least as great as the time 
it takes for one full light wave to pass the focal plane, results in our 
being able to discern the two stars as separate points. You've explained WHAT 
happens to cause this very well. But WHY it should be so is still a bit 
beyond my feel for the physics of it. 

Perhaps we could delve into this a bit more at some future time - unless I'm 
the only one in our astro group "nerdy" enough to be interested in such 
minutia! In that case, perhaps you could recommend a good reference source 
out there. I've picked up a few things on the internet, but so far it's been 
at too basic a level.

One other thought. Suppose we masked out the entire surface of the mirror on 
the FDO 16" scope - except for the last 1". (Leave a circle of exposed mirror 
that's 16" across, but only 1" thick.) Obviously, the light grasp would be 
drastically reduced - by 75% after including the central obstruction factor. 
You'd now have the light grasp of about a 4" refractor, and this alone would 
make seeing dim companion stars more difficult. But what about resolution? Is 
it solely that remaining surface, with sides 16" apart, that does the job? 
Reminds me of the theory behind interferometry - either optical or radio.

Thanks again, 
Doug
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