Stupid question about EFS/EF lenses

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AndyJC

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So, stupid question which I'm sure I used to know the answer to...

On a 1.6 crop body, if you use an EF lens (eg a 200mm prime) it gives you basically a 320mm lens. If you use a 200mm EFS lens on the same body.. does it give you 200mm or 320mm? I assume 200 as it's made for the 1.6 body and as such makes perfect sense for it to be actually 200.
 
The mm designation on a lens is the actual focal length of the lens, that is not affected by what body you use and is also not affected by being EF or EF-S. What has now become pretty standard to do is for people to equate things to a 35mm equivalent so that they can compare the field of view of different lens/camera combinations.

So a 200mm lens is always a 200mm lens, but if you use it on a crop body you get a narrower field of view making it look more like a 320 mm lens would look on a 35mm body, however aspects like depth of field are not the same as a 320mm lens on 35mm.
 
Do a search, it's been done to death already! The focal length is the focal length, it's the field of view that changes.

Still can't believe this is still 'cropping' up...
 
odd jim said:
Still can't believe this is still 'cropping' up...
Click to expand...
It's at times like this that I wish there were a 'Stone him to death!' smilie-thingy...
 
Hi Andy

I believe if you use an EF lens on a crop body you do not effectively use all the lens (i.e you use more of the centre not the edges), but if you use an EFS lens on a crop body you do.

But if you put a 200mm EF and a 200 EFS lens on a crop body your field of view will be the same. If you put the 200mm on a full frame body your FOV will be different to your 200mm on your crop Camera (the first full frame will look like a wider angle).

Hope that helps, and don't worry about the above two. There is no such thing as a stupid question!

Al
 
StewartR said:
It's at times like this that I wish there were a 'Stone him to death!' smilie-thingy...
Click to expand...

I thought it was good... :)
 
Soo...

If I have an 18-55mm kit canon lens on a 1.6body I have, at the widest zoom, a FOV of 18mm (Same as if I put an 18mm EF lens on a full frame?). If i put a 24-70mm EF lens on the 1.6x body - what would the FOV be at the widest ~38?

Thus should I get a 24-70 EF F2.8 L or a 17-55 F2.8 EFS lens?
 
AndyJC said:
Soo...

If I have an 18-55mm kit canon lens on a 1.6body I have, at the widest zoom, a FOV of 18mm (Same as if I put an 18mm EF lens on a full frame?). If i put a 24-70mm EF lens on the 1.6x body - what would the FOV be at the widest ~38?

Thus should I get a 24-70 EF F2.8 L or a 17-55 F2.8 EFS lens?
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Yes and no and no....... but not in that order, you are missing the relative part.

18mm is 18mm, but if you are talking about the 35mm equivalent to make a standard then 18mm on a Canon crop body has a FOV of about 29mm in 35mm terms. All lenses are marked with their real focal length, the crop factor is only something that people have added in later for them to make comparisons....... so if your lens says 18mm then if it is on a crop body it will look like a longer lens then if it is on 35mm, and if you had the option of 18mm on a medium format then that's going to be really wide as the sensor is quite a lot larger.

You are correct that the 24mm end on a crop body will give approx a 38mm equivalent in 35mm terms, now to answer if you should get a 24-70 or 17-55 it really does depend if you want wider angle or longer options.
 
Ah ok - so even an 18-55 EFS lens hasn't been adjusted to give you a field of view of 18mm (when compared to an 18mm on a full frame) - would have thought they'd have made it so it was 18 :/
 
Nope, all lenses, no matter what camera they are on are measured in mm, it is the physical property of the lens. Even little point and shoot cameras should have this measurement and you will see things like 5mm - 30mm on them. They might talk about a range that is in the 35mm equivalent but that's all it is.

Unless comparing cameras I would almost forgot about the 35mm equivalent. Someone shooting with a medium or large format camera doesn't (generally) take out their 80mm lens and think 'ah, that's my 50mm' even though the field of views are likely similar. Get used to the real focal lengths, sure, be aware of how to convert, I do when I sometimes shoot with 2 cameras and want to think about focal length crossover. I make my life harder as I have APS-C (1.6x crop), APS-H (1.3x crop) and full frame cameras so it keeps my maths working, however, as soon as I'm shooting I'm not worried about 35mm equivalents, I just use what I need for the shot.
 
AndyJC said:
Ah ok - so even an 18-55 EFS lens hasn't been adjusted to give you a field of view of 18mm (when compared to an 18mm on a full frame) - would have thought they'd have made it so it was 18 :/
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A number of people have told you the same thing with slightly different wording.

Stop. Think. Stop. Think again. Field of view is measured in degrees not millimetres.... The lens gives you the focal length, the sensor gives you the field of view.
 
In practical terms, the only difference between an EF lens and an EF-S lens is the mount. EF lenses will fit on all Canon DSLRs, EF-S lenses will only fit on crop cameras.
 
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