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Old 27-04-2008, 04:57 PM
B.Wilson
B Wilson

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differences in optical systems

As a newb could somene explain advantages/disadvantages of 300mm canon lens over 8 inch reflector over ed 100 if used on gem with good tracking. I thought aperture rules. Cost is not a factor.
Thanks for other information I have learned from other members.

B Wilson Swan Hill Vic
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Old 27-04-2008, 05:17 PM
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edwardsdj (Doug)
Doug Edwards

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Hi,

Apeture determines how much detail you can capture and how short your exposures will be.

A 300mm camera lens will have a very small apeture compared to either the 8" reflector or the ED100. This means longer exposures and less resolution if you can get the optical systems working at the same focal length.

You obviously get much less magnification with the 300mm focal length of the camera lens though, making it ideal for very wide field shots of whole constellations. An 8" reflector will zoom in on a much smaller part of the sky.

Have fun,
Doug
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Old 27-04-2008, 05:43 PM
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bojan
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Well, for the whole constellations, it is necessary to use even much shorter FL, say 70-135mm.
For example, Crux will fill the FOV of 135mm lens used on Canon 400D (See attachment).
For really wide fields I use 28mm, and for constellations 50mm lens.
Wide fields are a great fun.. :-)
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Old 27-04-2008, 06:13 PM
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edwardsdj (Doug)
Doug Edwards

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Sorry bojan, you are so correct. I assumed he meant a zoom lens but looking again at the post, I wonder if there is some confusion between apeture and focal length.
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Old 27-04-2008, 06:34 PM
B.Wilson
B Wilson

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Thanks for your responses Im not a photographer but wish to learn how to photograph what I see with my 10" dob

BW
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