Misinformation about m4/3

Started Feb 14, 2014 | Discussions thread
Sean Nelson
Sean Nelson Forum Pro • Posts: 12,866
Re: Tom, easy solution

Marty4650 wrote:

One thing we do agree on is that there is a crop factor involved. And that some crop factor must be applied in every single case when you use a lens on a different format camera than the one it was designed for.

This is a bit of a semantic argument, but I disagree with the idea that "crop factor" applies for lenses that are used on a "different format camera than the one it was designed for".   And that's because the normal use of term "crop factor" is to derive the field of view of the lens as expressed in terms of the focal length required to give the same field of view on a 35mm full-frame camera.

My Panasonic 20mm f/1.7 was designed for my M43 camera, yet it still has a 2X crop factor because it gives the same field of view as a 40mm lens used on a 35mm full frame camera.  No, it's not "cropped" in the sense that I don't get to use the lens's entire imaging circle.   But it is the same field of view as that hypothetical 40mm full frame lens (other factors, such as aspect ratio, being equal).

As such, "crop factor" is really dependent on the sensor size and has nothing to do with the lens beyond whether or not its image circle covers the sensor.

If we all expressed fields of view in terms of angular degrees instead of "35mm equivalent focal lengths" then we wouldn't need to worry about "crop factor" at all, at least not for describing fields of view.

Now you may disagree with this use of the phrase "crop factor".   But if that's the case, then I have to ask you what other term would you use to describe the relationship between various sensor sizes and the fields of view of lenses used on them?

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