DX/EF-S versus Full Frame focal lengths?

[rexbobcat]

I'm just curious.....if there are lenses that ONLY work with crop sensors such as the DX and EF-S lenses and Nikon and Canon had, then why are they still labeled with the full frame focal length? If a lens is 18-55mm, and the crop sensor equivalent is about 28-90mm, then why don't they just label the lens as the actual length that it is on a crop sensor, since that is the only size of sensor that the lens will work with?

Maybe this is a stupid question. :P

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[gryphonslair99]

Focal length is focal length. Physics do not change because of sensor size.

Focal Length of a Lens
Understanding Camera Lenses

[kundalini]

Because focal length does not change. 50mm is 50mm. Period. The effective Field of View from a DX and FX lens does thiough.

[rexbobcat]

Yes, but why don't they just label it as the effective FoV? I guess it's a matter of what a lenses focal length physically is as opposed to the focal length that it truly represents in an image.

I mean, the physics may not change, but the physical image does. It just seems kind of pointless to have crop sensor lenses if in reality they offer the same FoV of the full frame lenses.

[2WheelPhoto]

Keep coming back.

[rexbobcat]

Keep coming back.

What?

[usayit]

Yes, but why don't they just label it as the effective FoV?

Because they want to confuse people who go by the username "rexbobcat".... joking...

"equivalent" FOV... then one has to ask equivalent to what? Don't get hung up on it... its just a way to help older 135 film folks to relate to smaller sensors then it just stuck. At least the medium format guys are smart enough to figure it out without having to translate to another format.


besides....

If they did.. then those shooters who have never shot with full frame would ask

"WTF do they put equiv FOV focal length on a lens that only is for crop sensor?"