Can anyone explain lens focal length on cropped sensor

BIGEYE

BIGEYE

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I have a Canon EF-S 10-22mm lens that I have been using on my 60D. Now this lens is made for cropped sensor cameras, and so the focal length should be multiplied by 1.6. This makes an effective focal length of 16-35mm on a cropped sensor.
As this lens cannot be used on full frame, only a cropped sensor, why not just call it a 16-35mm lens?
 
Because not all Canon cameras have the same crop ratio?
 
BIGEYE said:
As this lens cannot be used on full frame, only a cropped sensor, why not just call it a 16-35mm lens?
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Because it isn't. The focal length of the lens doesn't change. It's the camera body which dictates how much of the scene it captures.


Steve.
 
The focal length is the same but you just get a smaller portion of the image, if you have a 50mm lens on a FF camera and a 30mm (48mm eq.) lens on a crop the pictures will not look the same.

Keeping all focal lengths to the 35mm is a lot more logical.
 
The focal length is a specification of the lens and nothing to do with the camera.
A lenses focal length is the same whether on a full frame camera or a crop sensor camera. It is just the field of view that differs as the crop sensor captures less of the image.
This narrower field of view is what is reffered to as a equivalent focal length.
 
BIGEYE said:
I have a Canon EF-S 10-22mm lens that I have been using on my 60D. Now this lens is made for cropped sensor cameras, and so the focal length should be multiplied by 1.6. This makes an effective focal length of 16-35mm on a cropped sensor.
As this lens cannot be used on full frame, only a cropped sensor, why not just call it a 16-35mm lens?
Click to expand...

The focal length of the lens is the same no matter what you fit it to. It just is what it is so they stick with the correct name... 10-22mm.

Your 60D has an APS-C sensor which is smaller than a FF sensor. So...

Imagine a FF sensor... someone takes some black sticky tape and tapes off the top, bottom, left and right hand sides. What you now have is an APS-C sensor.

The lens is the same, it's a 10-22mm, but you can't see the top, bottom left and right because of the sticky tape so it looks like a 16-35mm.

Becuse you can't see the top, bottom, left and right Canon don't include the glass in that area of the lens, they leave it out and call it an EF-S lens and although it'll work just fine on an APS-C camera if you could mount it on a FF camera the missing glass would mean that not all of the sensor would receive light and you'd get heavy vignetting or indeed just a black ring with an image in the middle.
 
woof woof said:
The focal length of the lens is the same no matter what you fit it to. It just is what it is so they stick with the correct name... 10-22mm.

Your 60D has an APS-C sensor which is smaller than a FF sensor. So...

Imagine a FF sensor... someone takes some black sticky tape and tapes off the top, bottom, left and right hand sides. What you now have is an APS-C sensor.

The lens is the same, it's a 10-22mm, but you can't see the top, bottom left and right because of the sticky tape so it looks like a 16-35mm.

Becuse you can't see the top, bottom, left and right Canon don't include the glass in that area of the lens, they leave it out and call it an EF-S lens and although it'll work just fine on an APS-C camera if you could mount it on a FF camera the missing glass would mean that not all of the sensor would receive light and you'd get heavy vignetting or indeed just a black ring with an image in the middle.
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There is no missing glass on an ef-s lens, it is simply designed to project a smaller image circle on to the chip which is why it doesn't cover an ff chip.
 
^^youve said exactly the same as woof woof just in a different way:)
 
Brachytron said:
There is no missing glass on an ef-s lens, it is simply designed to project a smaller image circle on to the chip which is why it doesn't cover an ff chip.
Click to expand...

And it does so with less glass.
 
BIGEYE said:
As this lens cannot be used on full frame, only a cropped sensor, why not just call it a 16-35mm lens?
Click to expand...

Because it's not a 16-35, it's a 10-22.

If I crop the centre 1037 x 691 pixels from my 7D images does the lens suddenly change from a 10-22 to a 50-104mm? According to some people's logic it should change - my image now has the same field of view as a 50-104mm lens would give on a 35mm camera.

Crop factor is totally pointless unless you're used to shooting with a different format. Otherwise it's less painful and completely legitimate to ignore it.
 
hollis_f said:
Crop factor is totally pointless unless you're used to shooting with a different format. Otherwise it's less painful and completely legitimate to ignore it.
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I think it's pointless even if you do use different formats.

I use 35mm, 120 (in three sizes) and 5x4 film. I don't think of the 120 or 5x4 in 35mm terms, I just know what the standard lens for each format is and work from there.


Steve.
 
I find the crop very useful to know.

In fact I wish I'd known all about crops when I bought my first DSLR lens as I wouldn't have bought a zoom lens starting at 28mm for my 300D. In fact I don't think the salesman knew about it either as he told me that to go wider I'd need a fisheye.

If you've never used an interchangable lens camera before then you'll be in the hands of the salesman or will need advice from elsewhere but if you grew up using 35mm cameras of course it helps to know that your next possible purchase is a x1.5 or x2 crop or whatever it happens to be as it helps you visualise the FoV you'll get from a lens and choose wisely.
 
Actually changing lens focal length while standing in same location does not change perspective, but moving the camera does and difference in these sensor sizes causes different visual effects.
 
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