All this talk about "equivalence" is silly

Started Jun 10, 2011 | Discussions thread
tko Forum Pro • Posts: 12,590
you read, but did you understand?

Case 1: if you want to stop action, in the same lighting condition, with the same ISO, a f/2.8 lens gives you the same shutter speed on a crop sensor or a FF sensor, so to same something like a 300 f/4 lens is "equivalent" to a 420 f/5.6 lens is completely misleading.

No. You forgot ISO. Since you can go with a higher ISO for the same noise, you can use a F5.6 on your large sensor instead of a F2.8 and get a similar looking photo.

Using a F2.8 lens on a crop sensor and a FF sensor will give you (1) a different DOF and a (2) a different amount of noise. They are NOT equivalent.

Case 2: if your primary concern is reach, then a 300 f/4 lens is decidedly similar to a 480 f/4 lens on a 1.6 crop camera, not 480 f/5.6.

Nope. . You start to talk about reach, then use aperture as an example. What does aperture have to do with reach? Nothing. DOF is controlled by aperture, not reach. F4 and F5.6 will give you the same DOF, 300MM and 480MM will give you the same reach.

Anyway, I can go on. But I think this "equivalence" talk is very confusing to beginners and causes more harm (confusion) than good (clarification).

Well, obviously it is confusing to many people. But that doesn't make it any less true. It's a basic fact, like F-stop or EV. Should be taught in any photography class. Just follow the rules to adjust ISO, F-stop, and FL between different sensor size systems. It's not perfect, but it's the best way to make similar images.

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