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Re: Question About Crop Factor Differences

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Todd Terry
Re: Question About Crop Factor Differences
on Apr 2, 2016 at 5:56:40 am

Ehh... I think you're thinking of things in a little bit of a wacky way, or at least a way that I've never quite heard anyone put it.

A couple of things...

[enrique bartolo] "is there any changes in quality that makes a difference because of one sensor being bigger for the lens and vice versa?"

Don't think of the one-bigger-than-the-other thing in reference to the lens/sensor, that is irrelevant. But, when using a 16mm sensor vs. a 35mm sensor, keep in mind that the 16mm sensor is only using the very center of the lens, where the "sweet spot" is, so it's possible the same lens might look sharper on the 16mm camera (although of course the field of view is radically different).

[enrique bartolo] "And lets also assume the crop factor on both cameras is by 3, therefore 35mm will be a fixed focal length of 105mm on BOTH cameras."

Not quite following you there. I'm not sure why you are saying the 35mm lens will be a 105mm. A 35mm lens (or whatever focal length) is a 35mm lens no matter what size sensor you are using... that doesn't change the focal length. BUT, because a smaller sensor only uses a smaller portion of the image, the field of view (as said above) will be radically different depending on the sensor size. For example, that 35mm lens will be medium-widish on a S35mm sensor camera... but the same 35mm lens will be quite a telephoto if mounted on a camera with a small 1/3" sensor. Sometimes people will say something like it's the "equivalent of a 50mm lens" or whatever, but that's really a very consumerish way of expressing that and not a legit cinematographic way of looking at it. Focal lengths are what they are, they don't change.

[enrique bartolo] "lets say I have a Micro Four Thirds prime lens with a focal length of 35mm...Now lets also assume the lens mounts into the Pocket Camera and the a7 (with an adapter) just fine."

You can't assume that though, and it likely won't. Well, it might mount, but it might not cover... two very different things. Lets take the example of a two film cameras, a 16mm and a 35mm, both with PL mount. One might think that all PL mount lenses would work with both cameras, but they wont (although they would all mount). All lenses designed for 35mm cameras would work on either, but lenses designed for 16mm cameras would only work on the 16mm... because they do not project a big enough "circle" of the image to completely cover the 35mm frame. The same thing will happen on a lens designed for a MFT camera. Assuming it mounts, it will definitely work on the Pocket Camera with it's small sensor. But a full-frame or 35mm sensor is bigger than a MFT sensor, so the MFT lens might not cover the 35mm frame. You'd likely get clipped corners or vignetting when using it with a sensor larger than MFT size.


Todd Terry
Creative Director
Fantastic Plastic Entertainment, Inc.

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