Quote:
Originally Posted by multiweb
To recap you want more light in get more aperture. ....
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Well, I still don't think that's the full story... would it not be more correct to say: "you want more light in get more aperture (for the given focal length)" ?
If you have an 8" at 200mm focal length, as you say it is putting the light across a smaller area hence intensifying the light per pixel hence brighter image.
If you have an 8" at 2000mm focal length, the light is spread out more, so you will not get as bright an image.
An 8" at 200mm is F/1, and 8" at 2000mm is F/10.
Right?