Like many do, don't lose sight of the arcsec/pixel combination Mike. Your telescope and camera are one. They should compliment each other, not work against. As the focal length changes, so will the arcsec/pixel value. By all means you can image DSOs at .25 arcsec/pixel, but will be wasting sensitivity with little gain to resolution (due to seeing limitations). A higher arcsec/pixel such as 2 or so will capture more light per pixel increasing sensitivity. Too high and you'll lose resolution. This is the reason why on the end of many long focal length instruments, you'll find cameras with 16u - 24u+ pixel size. They are a better match for the telescope focal length.
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