Originally posted by flyer The "crop factor" is absolutely useless.
Yves, it doesn't look like we will be able to convince each other. I won't prolong this but let me give me one more example:
You are interested in portraiture and read that the classic range recommended for portraiture is 85-135mm. But you own an APS-C camera and while you could mount a lot of lenses in the range of 85-135 on your camera, you should rather be mounting lenses in the range 55-87. That doesn't sound "totally useless" to me, unless you want everyone to rediscover what has been discovered in the FF world.
Originally posted by flyer It just keeps people in the 35mm bubble.
I'd say it allows people to learn from 35mm experiences.
Originally posted by flyer A 50mm lens is a 50 mm lens.
Of course, only beginners think that a focal length could change. However, "50mm" doesn't mean anything. The only meaning "50mm" has is its association with a certain AOV. If we used AOV to refer to lenses then we could say "I love my 46.8° AOV lens" and that sentence would make sense independently of the format.
If someone says "I love my 50mm lens" (on FF) then this has to be translated. We could translate the sentence to refer to an AOV but since most photographers talk about AOV in terms of the focal length associated with it, we use a focal length that represents that AOV. Since it is a different focal length on a different format, the "crop factor" comes into play.
Originally posted by flyer The angle of view will be different, and you need to get used to that, but the focal length didn't change.
I agree that anytime one uses a focal length that was obtained by using a crop factor one should qualify it with the term "<old format>-equivalent", e.g., "50mm FF-equivalent".
Originally posted by flyer When working with an APS-C size sensor/film, you should get used to what a specific lens will do on your camera. Trying to compare to 35mm all the time is just handicapping you.
I fully agree with the first statement. The second doesn't apply to me and, I feel, not to a lot of other photographers either.
Originally posted by flyer You must associate the word to the idea it represents, not to it's translation.
I see your point but note that there are a lot of books that associate words to translated words (not to the ideas they represent). These books are called "foreign language dictionaries". Are they useless?