Hi Guys! Your answers to my earlier questions regarding F numbers and shutter speeds and ISO's for DSLR's are great! However there is one last query I can't seem to work out too well, and that is, that with my super fast lens on my Pentax of 1.4, I can get an almost passable picture of the crooked J in Scorpious at 40 seconds and F1.4. My little camera lens is a mere 2.5 inches diameter. Now I realise that most telescopes are lucky if they have F4 numbers, so an equivalent exposure to my 40 sec at F1.4 will be about 320 sec (over 5 minutes), BUT on the other hand, the telescope will have a much larger diameter lens and so will be able to concentrate all that light from its large aperture, onto the CCD chip. So how come some folk take humungous numbers of shots maybe totalling 1 hour or more. Why doesn't all that light overexpose the photos and turn them all white? Is it because the scope is looking at a much dimmer location?? (But...M42 isn't that dim though?) I guess that must be it then! Am I right??
Answers please on a postcard
