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09-12-2007, 03:38 AM   #16
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Kguru, I like your logic, makes sense to me. Gives us a constant value which compares what really matters, that is, how does it affect my photo.

09-12-2007, 06:02 PM   #17
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QuoteOriginally posted by DMH Quote
Kguru, I like your logic, makes sense to me. Gives us a constant value which compares what really matters, that is, how does it affect my photo.
Also too confusing, since so many different versions of "X" exist, and even the definition of "normal" for 35mm has a small amount of leeway.

Focal length is focal length, PERIOD, and is the number that should be on the lens. It should be up to the photographer to know whether or not they have a cropped field of view or not.

Many other aspects of a photo are still dependent on the actual lens focal length and not it's "35mm equivalent", such as depth of field. DOF remains based on lens focal length, not "35mm equiv" focal length, while field of view is based on "35mm equivalent" focal length.

That is to say that a 50mm lens will deliver the same DOF regardless of what sensor size it is used with. The field of view will differ depending on sensor size though.
09-12-2007, 07:46 PM   #18
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QuoteOriginally posted by Kguru Quote
In the "old money" 50mm was the mid-point between W(ide) and T(ele) so I tend to think:
17mm=3W, 20mm=2.5W, 28mm=1.8W
70mm=1.4T, 100mm=2T, 300mm=6T

With APS-C mid-point is 33mm therefore:
17mm=2W, 20mm=1.7W, 28mm=1.2W
70mm=2T, 100mm=3T, 300mm=9T

It's simpler to say 70mm in APS-C is 2x Tele rather than it's equivalent to 100mm focal length in 35mm system.
It also readily explains 28mm= 1.2x Wide is no longer very wide.
Actually, it you should change "T" to "S", and not use "W" at all, because the FL is a fraction or multiple of "S"tandard (human binocular field of view equivalent:-)

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