Quote:
Originally Posted by M54
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?
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Molly,
Great insight. And it's the terminology that's causing the confusion.
A relatively short focal length in comparison to the aperture size is often referred to as a short focal ratio. This is where the confusion comes in. As, for example, the Hale Telescope has a short focal ratio but a long focal length. That's why I like Troy's point of using fast for a short focal ratio to save confusion with focal length. A relatively long focal length in comparison to the mirror size is often referred to as a long focal ratio but the term slow would again save confusion with long focal length. For example, an 80mm aperture, f/10 telescope only has an 800mm focal length.
Regards, Rob