Crop sensor

Identityxp

Identityxp

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Adam Skitt
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I have a canon 800D and I am looking at getting a sigma f/1.4 35mm art DG HSM. I have read that this lens works on a crop sensor but does that mean I still times the focal length or will I have the view of 35mm??
 
So no matter what lens i choose i will always have to give it a 1.6 crop factor?
 
Yes, the crop factor is camera dependant not lens dependant. All Canon APS-C sensors have a 1.6x crop factor. Nikon 1.5x crop factor.
 
Identityxp said:
So no matter what lens i choose i will always have to give it a 1.6 crop factor?
Click to expand...

The lens will still be a 35mm, the field of you that you get on a cropped sensor will differ from what you would see on a full frame sensor. You do not have to calculate unless you run the lens on both regularly. People insist on this 'equivalence' in terms of full frame, but if you never actually use full frame or don't plan to, then it shouldn't matter.
 
I'm not sure that the OP, @Identityxp, really understands what crop factors mean. Let's see if I can explain.

The first thing to note is that the focal length of a lens is an inherent physical property of the lens. It doesn't matter whether the lens was designed for a full frame camera, crop sensor, medium format, or whatever. It doesn't change depending on what camera you're using. A 35mm lens is a 35mm lens is a 35mm lens, simple as that.

Mount your 35mm lens on a full frame camera (i.e. a camera with a sensor measuring 36mm x 24mm) and you'll get a moderately "wide angle" field of view - in fact the horizontal field of view is about 57°. But on a crop sensor camera it behaves differently. It's exactly as if you had cropped the edges of the full frame camera's picture, leaving you with the bit in the middle. It's a narrower field of view. For a Canon crop sensor, which typically measures about 22.5mm x 15mm, the field of view of your 35mm lens is now about 36°. It's not really a wide angle any more; it's behaving more like what we'd call a "standard" lens.

And here's where the crop factor comes in. The angle of view - and therefore the framing, or composition - you get when you mount the 35mm lens on a crop sensor camera is the same as you'd get if you had stuck with the full frame camera and put a longer lens on it instead. How much longer? Well, the way the geometry works out, the focal length multiplier is the same as the ratio of the sensor sizes. So for Canon crop sensors it's about 36/22.5, which is 1.6. Hence the view you get with the 35mm lens on a Canon crop sensor is "equivalent" to the view you get with a 56mm lens on a full frame camera.

And that is the *only* time you need to think about crop factors - when you're looking at two different cameras with differently sized sensors. For example if you really like the look you get with a 35mm lens on a crop sensor camera, but you're thinking of switching to a full frame camera, then you'd need a 56mm lens to give you the same framing. But if you're only using one camera system, you really don't need to worry about it at all.

Does that make sense?
 
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