|
F Ratios ??
Some of you may have noticed that after my ponderings, I ended up with a 10" Bintel Premium dob which is still sitting faithfully in its box until 31st July, (birthday time) UNBELIEVABLE RESTRAINT, but it's ungratious to push for your own present....
Anyway, in the mean time I'm here pondering about stuff. Can anyone shed any light on the F ratio thing. My scope is 1250mm focal length and f/5. If a scope was 1250mm focal length and half the diameter it would be f/10, and suddenly really good for planets. So how come letting in a quarter of the light transforms this into a good planet viewer? And so then, if I cut a 5" hole in the end dust cover (theoretical here), why wouldn't it be equivalent to an f/10. I'm quite sure it isn't, but just pondering the theory.
PS After months of clear skies and a drought down here near Canberra, the day we bought the telescope it rained 35mm and hasn't really been clear since. But I fooled them......it's still in the box..ha ha...he he aaaAAARRRH
|