crop factor on older lenses

Started Jun 6, 2014 | Questions thread
Kim Letkeman
Kim Letkeman Forum Pro • Posts: 33,428
Re: crop factor on older lenses

micksh6 wrote:

yonsito wrote:

mbower wrote:

Ok, my next question -

I understand crop factor and that my 45mm lens is equivalent to a 90mm lens in the 35mm world.

But how do I calculate the crop factor for an older lens? I have the adaptor that lets me attach my Nikon 35mm prime to my M43s body.

What is the general crop factor that should be applied when one uses older lenses?


The crop factor depends on the size of the camera sensor, compared to a 35mm film. The lenses have nothing to do with it.

The focal length is an optical characteristic of the lens. The Olympus 45mm should always be a 45mm lens. Your Nikon 35mm is also always a 35mm lens.

The crop factor tells you what the field of view of a lens on your camera will be. The lens perspective, however, remains the same. This is important and it's why I don't think you should consider your 45mm lens a 90mm lens.

Forum members are sometimes helpful, but other times they can make a very simple matter too complicated.
Olympus states 35mm equivalent focal length 90mm on their 45mm F1.8 lens product page.
It could have been as simple as that.

Actually, not really.

For exposures, it is as simple as that. And for the 1/EFL rule for shutter speed, it is as simple as that.

But if they don't also mention the CF * aperture rule for subject isolation, then an important bit of data is still missing.

Hint to OP: do some research yourself. Search works.
Especially if you also plan to ask about equivalent aperture. Such questions make seemingly simple threads to grow above post limit.

Good explanation of the crop factor:

Good explanation of lens perspective:

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