Quote:
Quote:
Quote:
Originally Posted by Alchemy
400-750mm short
750-1250mm medium
1250-2000 plus long
f5 and below fast
f5 to f8 midrange
f8 to f15 plus slow
|
|
Quote:
There is still some confusion over the terms fast and slow as against short and long. I prefer Troy's use of the terms fast and slow with focal ratios. An f/5 scope with large aperture can have a longer focal length than a f/10 scope of small aperture.
Focal lengths can be shorter or longer, but the absence of a defined scale makes this is an even more contentious area. Just where does a short focal length range end ... at 750mm or 900mm or ? And where does a long focal length start?... the 200-inch (5.1m, f/3.3) Hale Telescope on Mt Palomar has a 16.8m focal length.
Regards, Rob
|
|
Am I beginning to suspect that whether a focal length is short or long is entirely dependent on the relationship to its aperture?
So the 5.1M Hale Telescope would have a short focal length when related to its mirror?