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mmm whilst admitting I know jack about astro imaging, I find this all odd. When it comes to terrestial imaging, the exposure triangle (aperture, iso, shutter speed) all come into play. As an example, a 500mm f4 telephoto lens, used at 1/1000 second, ISO 400 and f4 will provide twice as much light as the same shutter speed and iso but f5.6. Why is it different for astro imaging? Logic indicates to me that f stop (at the same focal length ratio and aperture) *does* make a difference. Not so much in the amount of light hitting, but in the amount of time required to hit a particular level of exposure. I fail to see why astro imaging is any different to terrestial, digital or film be damnéd.
Dave
edit: so a f3 10" newt will gather light twice as fast as one that is one stop slower in terms of f ratio (but same aperture, i.e 10"). Am I just misunderstanding what you guys are all saying, or just completely off track here with my thinking?
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