ICY SCIENCE: SCIENCE SPACE ASTRONOMY Spring 2014 | Page 10

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My telescope has an f-ratio of f/15 - its written on
the tube, so 127 x 15 means the focal length of the
objective is 1905 mm.

Now, where were we. Oh yes magnification. So
with a 26mm eyepiece, I have 1905/26 = 73. So
I have 73x magnification. If I put a 9mm lens in, I
get 211x. My smallest lens is a 6.4mm one, which
would therefore give 298x magnification. All well
and good, but I rarely use this eyepiece, and I’m
sure if you have similar you know why too. You get

Above: Airy disk - simulated, credit wikipedia

terrible results. The focusing is dreadful, balanced
on a knife edge. The image is typically blurry, and
when all is said and done, a star looks like a dot,
no matter how much you magnify it. Interestingly I
know people with 200mm objectives, much bigger
telescopes. They have a focal length of 1000mm, so
a 26mm lens on that would be 38x. So bigger mirror,
more impressive size, less magnification! Weird!

I could get a 1 mm lens, and have it magnify 1900x
- but it wouldn’t be worth bothering with. You can
get any magnification you like, just like you can blow
up a digital image to any size you like - but beyond
ICY SCIENCE | QTR 2 SPRING 2014

Below: Airy disk from a laser passing through a pin hole
- Wikipedi