I am confused about Crop sensor ratios and their impact on EF-S Lenses

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Hi All,

I was asked this question by someone who thought I knew a lot about Canon gear (fool!).

Anyways, I know that if I put an EF Lens (like my 16-35mm) on my 7d I know that I should multiply the focal lengths by 1.6 i.e the Lens really acts as a roughly 25-56mm. Now does the same apply to EF-S lenses as they are specifically designed for the crop frame cameras (I could not use it on a FF 5D) so does this still multiply?? i.e Is this really a 16-35mm Lens when it is fitted to my 7d?

Sorry to ask stupid questions, but I really don't know the correct answer and am curious.

Many thanks in advance
 
Please dont let the Crop factor confuse you.. The factor is only a comparison to a full frame camera using the same lens, so the images taken by both cameras will be different when printed out as the full frame camera is using the whole of the EF lens, where the 7D will look like its cropped the image as its only using a smaller section of the lens, the EFs lenses have smaller Diameter glass in them, so can not be used on full frame camera's so there is no crop ratio anyway..

Just remember what you see through "YOUR" viewfinder is the shot you will get, whether an EF or EFs lens,
 
Please dont let the Crop factor confuse you.. The factor is only a comparison to a full frame camera using the same lens, so the images taken by both cameras will be different when printed out as the full frame camera is using the whole of the EF lens, where the 7D will look like its cropped the image as its only using a smaller section of the lens, the EFs lenses have smaller Diameter glass in them, so can not be used on full frame camera's so there is no crop ratio anyway..

Just remember what you see through "YOUR" viewfinder is the shot you will get, whether an EF or EFs lens,

Thanks for the reply Steve, but I think you missed the point of my question. I know that if I use an EF Lens on my 7d it crops out some of the outer range of the lens due to the sensor which creates an effective multiplier for the focal range and I get this.

My query is that if the EF-S lenses ONLY work on cropped frame cameras are they really designed as 10-22mm when used on that body. I.E if I wanted to replicate the image as seen from the exact same same position with a FF Camera would I need a 10mm lens or a 16mm. Do you see where I am coming from?

Its not important to my photography as I can always move around or zoom to get the composition that I want, but with a curious mind I am keen to know the real answer.
 
An EF-S 50mm and an EF 50mm are the same fl; 50mm. The EF-S lenses rear element protrudes further into the body to better cover the sensor. This protrusion is why they won't work on FF bodies. So, yes, you still take crop factor into account. And yes, I realize there is no EF-S 50mm, it was for example only.
 
An EF-S 50mm and an EF 50mm are the same fl; 50mm. The EF-S lenses rear element protrudes further into the body to better cover the sensor. This protrusion is why they won't work on FF bodies. So, yes, you still take crop factor into account. And yes, I realize there is no EF-S 50mm, it was for example only.

Thanks very much for the clarification. Exactly the answer that I was looking for.
 
I posted a few pictures in another thread to illustrate this fact : 50 mm is 50mm, regardless of whether it's on a crop sensor body or not. If you take a 50mm lens, say the EF 50 1.8, and take a shot, and then put on, for example, the EF-S 18-135 lens, zoom it to 50mm, and take a shot, you will get EXACTLY the same frame that you got with the 50mm EF lens. You DO NOT get a "telephoto" view, or a "magnfied view", or 1.6x of anything, when you are using a crop body camera.

What you DO get, though, is the field of view that is roughly the same as one you would get if you had a lens 1.6 times the focal length, on a FULL FRAME camera. In other words, 50mm on a crop sensor looks like 80mm does on a full frame camera. But it is NOT 80mm on a crop body.
 
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CanonJim said:
I posted a few pictures in another thread to illustrate this fact : 50 mm is 50mm, regardless of whether it's on a crop sensor body or not. If you take a 50mm lens, say the EF 50 1.8, and take a shot, and then put on, for example, the EF-S 18-135 lens, zoom it to 50mm, and take a shot, you will get EXACTLY the same frame that you got with the 50mm EF lens. You DO NOT get a "telephoto" view, or a "magnfied view", or 1.6x of anything, when you are using a crop body camera.

What? I'm pretty sure this is wrong.

The only difference between ef ad ef-s lenses is the back element is closer to the mirror and the lens produces a smaller image circle. You still get the magnified view no matter what at the same focal length because the image circle is smaller.

Edit: ok now I'm just confused by what he said. Seems to contradict himself... Maybe lol
 
As said - focal length is focal length. The focal length of a lens is not affected by the sensor or film size behind the lens. As a result 50mm is always 50mm - no matter if its a lens designed for crop sensor, fullframe (35mm film), medium format or large format. What does change is the area of the frame that is captured. Now a lens for a larger sensor/film size has to cast a larger image circle into the camera so that it can record the whole image. As a result your EF lenses are larger than your EFs as more glass is needed to reflect those bigger image circles (although saying that many EFs lenses can still cast a pretty big image circle - however those edge zones will be significantly softer and less well corrected against distortions and aberrations).

There are also other physical differences and, as said, with Canon the EFs lenses have a protruding rear element which, when mounted to a fullframe (35mm) camera body can result in damage to the mirror inside the camera as it flicks up to take a shot. Some can be modified to work on fullframe bodies, however not all can. Note also that almost all 3rd party lenses use the EF mount shape rather than the EFs mount shape even on their crop sensor only lenses (which still have the protruding rear elements and thus shouldn't be used on 35mm/fullframe cameras).


Remember in the real world there can be differences when comparing lenses which have the same focal lengths. Focal length is measured when the lens is focused to infinity and many lenses will actually reduce their effective focal length once you start to move into close distance focusing. As a result comparing a 50mm lens to a 50mm lens at close distances might show some difference in the frame captured even if nothing else changes. You might also see small differences, even at infinity, as a result of manufacture tolerances

Furthermore when it comes to zoom lenses remember that the mm markers on the barrel are not always exact. The wide and long end are normally accurate, but the middle points can have some variation, so comparing a 50mm prime to a zoom set to 50mm might, again show some differences.
 
If you put a EFs 10-22mm lens on a crop camera, you still multiply it by 1.6 and come up with the equivalent field of view of a 16-35mm on a full frame camera.
 
Ok, let's try this one more time. There is a common misconception that when you put a XX mm focal length lens on a crop body camera, you can multiply the XX by the crop factor, fooling yourself into thinking you have a 'greater' focal length lens. This is simply not true. Here are two pictures, taken on my crop sensor 50D. One was taken with a 100mm EF lens. The other was taken with an 18-135mm EF-S lens, but EXIF info shows it to be at the 100mm focal length. Both images have exactly the same field of view.

Now, here's the kicker. If I put a 100mm+ lens on a FULL FRAME camera, and set it to 160mm, it would show just about exactly the same field of view ON THAT FULL FRAME CAMERA, as both of these 100mm lenses did on my 50D.

That's the "crop factor". I know, it kinda sounds backwards, but that's because the camera companies tried to pull a fast one on the consumer when crop bodies came out by telling you that you'd have a 'multiplication', or 'telephoto' lens automagically appear on your crop sensor camera. That is not true. The crop factor is only in play WHEN COMPARED TO A FULL FRAME CAMERA.

This has nothing to do with the mechanical differences in the construction of an EF-S lens versus an EF lens, and they have nothing to do with the differences in sensor size and image circle.

Please, look at these two images. They are both 100mm focal lengths. The 100mm focal length lens does not look like 160mm on a crop sensor body.
 

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If you put a EFs 10-22mm lens on a crop camera, you still multiply it by 1.6 and come up with the equivalent field of view of a 16-35mm on a full frame camera.
But you're not looking through a F/F camera! You're looking through a crop sensor camera. 10mm is 10mm. It's only if you could put that 10-22 EF-S on a F/F body (which you can't) that it would give you a 16-35mm FOV. On the crop body, it's giving you 10-22mm.
 
CanonJim, you're just confusing the issue needlessly. The OP got the answer from Subscuck already, and a few others just reitterated it.

Put a prime lens on a full frame camera and take a shot. Now put the same prime lens on a crop body camera. Field of view is different by a factor of 1.6x, which is the "crop factor" of a crop-sensor camera body.

Put the EFs 10-22mm on a full frame camera (if you could) and your field of view would be 10-22mm, but just like the prime lens, on a crop factor camera, it's 1.6x = 16-35mm for the field of view. If you don't believe me, you can look it up on the Canon site.

That doesn't mean that you get extra zoom power by 1.6, and nobody's saying it does. It's a CROP factor, not a ZOOM factor.

But all that doesn't answer OP's question in any way though. He just wanted to know if the field of view is calculated as a 1.6x factor on EFs lenses on a crop factor camera, like it is with regular EF lenses on a crop factor camera. Answer: Yes.

That simple.
 
If you put a EFs 10-22mm lens on a crop camera, you still multiply it by 1.6 and come up with the equivalent field of view of a 16-35mm on a full frame camera.
But you're not looking through a F/F camera! You're looking through a crop sensor camera. 10mm is 10mm. It's only if you could put that 10-22 EF-S on a F/F body (which you can't) that it would give you a 16-35mm FOV. On the crop body, it's giving you 10-22mm.
No, it's not. You've got it backwards. You're giving out incorrect information. Go to the Canon site, look up the lens, and see for yourself.
 
If you put a EFs 10-22mm lens on a crop camera, you still multiply it by 1.6 and come up with the equivalent field of view of a 16-35mm on a full frame camera.
But you're not looking through a F/F camera! You're looking through a crop sensor camera. 10mm is 10mm. It's only if you could put that 10-22 EF-S on a F/F body (which you can't) that it would give you a 16-35mm FOV. On the crop body, it's giving you 10-22mm.
No, it's not. You've got it backwards. You're giving out incorrect information. Go to the Canon site, look up the lens, and see for yourself.
I didn't say you were wrong - it's just that I don't think its USEFUL to think in terms of the equivalent FF image circle when you're looking through a crop sensor body. That's like sitting in a Toyota Celica with the accelerator pressed to the floor, and thinking, "oh, If I was in a Ferrari, with the pedal pressed to the floor, I'd be going faster." Yeah, maybe true, but it has no bearing whatsoever on the current situation.

And are you saying that the 10-22 EF-S lens is really 16-35 mm ? Then why isn't it labeled 16-35mm?
 

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