Crop factor question

minicoop1985 · Jul 3, 2014

OK, we're all aware that there's a 1.5x crop factor between a Canon 7D and a Canon 5D mk. III. Well, I have a slightly different question. I have an 80mm f2.8 medium format lens I've been sorta mounting on my 7D. I was wondering... Since it's not a standard 35mm full frame lens, does the crop factor here change? What does this 80mm now become? If it helps, it's designed for 6x6.

Derrel · Jul 3, 2014

IT IS STILL an 80mm lens. The FOV equivalence in 135 format would be spec'd as 80mm x1.6= 128mm equivalent field of view angle in 135 AKA "24x36mm" format.

Your 80mm lens will ALWAYS REMAIN an 80mm focal length lens. It just happens to be an 80mm that can "cover" a large-ish piece of film.

minicoop1985 · Jul 3, 2014

Derrel said:
IT IS STILL an 80mm lens. The FOV equivalence in 135 format would be spec'd as 80mm x1.6= 128mm equivalent field of view angle in 135 AKA "24x36mm" format.

Your 80mm lens will ALWAYS REMAIN an 80mm focal length lens. It just happens to be an 80mm that can "cover" a large-ish piece of film.

FOV change is what I meant-poor phrasing on my part. Wow, that's about the length I really, really need for a nice prime. Thanks, Derrel.

Vince.1551 · Jul 4, 2014

Sensor size determines crop factor

KmH · Jul 4, 2014

Canon APS-C crop factor is 1.6x. Nikon APS-C crop factor is 1.5x.

There is also a Canon APS-H size image sensor that has a 1.3x crop factor.

AlanKlein · Jul 4, 2014

Here's a little graphic I made to explain crop factors to myself. It shows how the same lens will double the telephoto zoom appearance on a 2x crop factor camera. Maybe it will help you.

AlanKlein · Jul 4, 2014

Both graphics are the same - only the size is different. Somehow I posted both.

Mike_E · Jul 4, 2014

So, you're putting a CZ 80mm Planar on a Canon, is that what you're doing?

If so, how is it?

minicoop1985 · Jul 4, 2014

It's actually older than a CZ Planar. I'm putting a Kodak Ektar 80mm f2.8 and a Mir 3 65mm f3.5 on there.

See, that's what I'm wondering-the crop factor of 1.5x applies to the APS-C vs the standard "full frame" 35mm size, but does it apply with APS-C to 6x6 medium format? That's what I'm getting at. I understand that a 50mm lens designed for a 35mm or full frame camera on a 1.5 crop factor camera will produce an equivalent field of view of 75mm on a full frame. I get that, it's just comparing the crop between MF and APS-C.

Mike, it works pretty well, actually. I made a cardboard tube adapter I have to hold on the camera to test this theory, and this is what I got:

Fractions by longm1985, on Flickr

I was a pretty good distance away, too. That's what brought me to this question.

greybeard · Jul 5, 2014

Yeah, it should produce the same image as any other 80mm on your 7d. The big difference is that it will produce an image that will cover a 2 1/4" format sensor were as lenses designed for 7d will only cover the much smaller 7d sensor.

Patrice · Jul 5, 2014

80mm lens on MF body is considered a 'normal' lens as is a 50mm on FX or 35mm on DX. You can compare diagonals of various formats to get 'crop factors' : DX diagonal 28mm, 135 (FX) diagonal 42mm, 645 diagonal 75mm, 6x6 diagonal 85mm. So 'crop factors' : DX-FX 42/28=1.5, FX-645 75/42=1.8, FX-6x6 85/42=2. The 'crop factor' is not related to lenses but to differences in sensor sizes. An 80mm lens, from any system of any size, will always give the same rendering when mounted on a DX camera because it's not the lens but the sensor which is at the root of the 'crop factor'.