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Old 18-09-2017, 10:29 PM
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alocky (Andrew lockwood)
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Join Date: Aug 2010
Location: perth australia
Posts: 1,289
The impact of aperture on resolution is pretty old news, the size of the airy disc is determined solely by the aperture of the telescope. This is because the hole in the end of the tube is a boxcar window filtering the wavefront coming towards us. Even if you don't know what a Bessel function is, the fact is, an infinitely wider aperture gives you a perfect spike response to a star, and a small aperture gives you a sort of ringing peak with sidelobes that would be a lot easier to draw than describe.
This leads to another of the frustrating myths - my 4" APO is better than a 25" dob because I can see the airy discs on a good night. The fact is, those discs are more than 6 times bigger in the 4"!
Now of course then you have the impact of central obstruction and all the other fun and games but these are secondary (excuse the pun).
Unfortunately, galaxies are small and faint.
And apart from Mike, we really aren't getting much out of the planetary nebulae yet! That's next challenge.
cheers,
Andrew.
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