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I have a Canon 550D with the standard 18-55mm kit lens. The 550D has a 1.6× crop factor.

My question is very simple but whenever I've asked before (Yahoo Answers) I always got overly-complicated answers which confused me even more. So here goes.

If I get the EF 50mm f/1.4 USM lens, will it be the same as setting my EF-S zoom lens to 50mm when attached to the 550D? Or will it be the equivalent of an 80mm EF-S lens?

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Welcome to the site, Ozzy. We've got a couple of questions already that cover this ground pretty closely. Specifically:, but also and a few others under the "crop-factor" tag: Does any of that help, or does it only add to the confusion even more? – mattdm May 4 '11 at 2:28
And also, also see… – mattdm May 4 '11 at 12:14

6 Answers 6

up vote 13 down vote accepted

I'm going to go with the very simple answer here:

The lens does not change. The f/1.4 50mm EF lens has exactly the same focal length (and everything that goes with that) as your EF-S zoom lens set to 50mm.

The "crop factor" is not useful for comparing different lenses on the same camera. It's only useful for comparing lenses across different camera formats — which means different film or sensor size.

And then, because I can't help myself, I'm going to go a bit further. This seems like overcomplicated nonsense, but it's actually both pretty simple (it only seems complicated — honest!), and a reasonably useful tool to know about.

So, in case you want to chase things further, once you're definitely unconfused and clear about the basics, see:

Which give some depth and background. But still, remember, the answer to your question is simple: focal length is a property of the lens, and you can't change it without more optics.

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thank you for the links, helped out alot :) so now that i got this out of the way... i just have to get used to shooting a 50mm prime O_O or might just get a 30mm 1.4 sigma XD – Ozzy May 4 '11 at 2:46
Cool, glad to help. So now, you want and :) – mattdm May 4 '11 at 2:49

The field of view (the picture you see through your lens) will be the same with any 50mm lens - regardless if its EF or EF-S.

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It will be the same as your zoom set to 50mm.

A 50mm focal length lens is a 50mm focal length lens, neither lens "knows" what sort of sensor you have behind it. It's just that the smaller sensor captures less of the projected image, so the resulting image is cropped. This is similar (but not the same) as what you'd get on an FX sensor with about an 80mm lens. This is true whether you are using an 18-55mm zoom at 50mm, or any fixed focal length 50mm.

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This was my favourite "simple" explanation for the whole crop factor thing. I like that you worded it "captures less". I feel like this is the most layman's way of putting it. That a 50mm is the same focal length regardless, but on APS-C and so on, it captures less. – Vian Esterhuizen May 4 '11 at 3:17

Both lenses are 50mm. the only real difference is that the EF-S can be a smaller piece of glass, because it need only illuminate a smaller sensor. The EF must be able to illuminate at full frame sensor, so it is a physically bigger piece of glass. This is the primary reason that EF-S lenses are less expensive.

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As the previous answers stated correctly, the Field of View (FoV) will be the same with the two lenses. That means that you will capture the same scene with the two. However, note that there is a difference in the maximum aperture between the lenses. The 50/1.4 will let you shoot in lower light, and can produce shallower Depth of Field (DoF) than the kit lens. It is also much sturdier than the kit lens.

I added this answer b/c your question was "...will it be the same as...". So, to be picky, no - it will not be the same, but it will be pretty similar.

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+1 you beat me to it by seconds... :) – John Cavan May 4 '11 at 3:03
There are other differences too: the EF 50mm f/1.4 is sharper than the kit lens, but like many prime lenses it lacks image stabilization. – Caleb Jun 18 at 4:50

Most of the answers above are misleading. A Canon APC sensor has a crop factor of 1.6 which effectively changes the focal length by 1.6, therefore a 100mm lens has an effective length of 160mm. A simple exercise is to use the same lens on two difference bodies, one full frame and one cropped and you will instantly see the difference.

You cannot use a full frame lens on a cropped sensor body if it is a Canon but you can if you own a Nikon. Nikons have a crop factor of either 1.5 or 1.7 for older models but crop (DX) lenses will still work on a full frame setup, although the image does not use the entire frame.

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What is misleading about the answers above? The majority specify that the lenses must be on the same body, which is specified in the question. – damned truths Jun 17 at 22:05
Of course you CAN use an "full frame lens" (supposedly, EF mount) on a a crop body (having EF-S mount). It is the other way that is not possible (i.e., you can use a EF 50mm on a EOS 7D, but you cannot use the EF-S 10-22mm on a 5D). – ysap Jun 18 at 19:40

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