1.3 vs 1.6 Crop factor

[kndreyn]

I've read here that the crop factor on digital cameras doesn't increase magnification. But comparing my D60's 1.6 to my 1D's 1.3 crop factor, I can definately see a magnification difference. Has anyone else done a side by side like this? Am I misunderstanding this?

[dhbailey]

There are various threads on this at this forum and elsewhere.

What happens, if I understand things correctly, is that a full size sensor capture the same amount of data as a 35mm film would. A sensor with a 1.3 factor means that the 35mm film area is 1.3 times as large as the sensor, and the same with a 1.6 sensor.

Think of it as simply chopping off some of the data that a 35mm full-frame sensor would capture. Imagine a ruler, where the 35mm camera would capture the full 12" stretching across the frame. If you then put a 1.3 sensor camera in the same location and took the same picture (assuming the same lens, camera mounted on the same tripod in the same location relative to the ruler) the camera's picture would only show the middle 9 inches (approximately). Now if both cameras produce the same size files, e.g. 8MB pictures, you have one picture at 8MB showing a full 12 inches and one picture at 8MB showing only the middle 9 inches. If you print them both at the same size, the picture taken with the 1.3 sensor will appear to be larger.

However, full-frame sensor cameras usually shoot larger MB pictures, so you lose the 1-to-1 relationship between the two pictures. The full-frame cameras shoot at 12MB or larger, so if you then crop THAT image to be 8MB in size by chopping the outer 1/3 (1/6 from each edge) and you will see the same thing as you see with the 1.3 sensor.

So it's not really that the 1.3 sensor magnifies the image, it just APPEARS to magnifiy the image. And since in photography it really is all about appearances, in one sense it does magnify things. But not actually, when everything is put on a 1-to-1 basis, the image isn't actually larger.

What that crop factor DOES do, though, is to reduce the size of the image you can get with the same lens. That means that you either have to move back if using the same lens to get the same field of view, or you have to use a shorter lens to get the same field of view from the same location.

That is where the 1.3 factor or 1.6 factor becomes important in deciding how to shoot a scene, especially for people who are coming to digital from the film world. So when you put your 50mm lens on a 20D, it becomes effectively a 80mm lens (50mmx1.6=80), with the reduced field of view that an 80mm lens would give. So to get the same field of view that you would get with a 50mm lens on a 35mm film body, you need to put a 32mm lens on a 20D body if you are standing in the same spot as with the film camera.

Again, since what we see is of utmost importance in photography, you are actually seeing a magnified image, when both images are printed straight to paper. But if the images are made to be the same size by cropping the larger file to equal the smaller file, there isn't really magnification.

[CyberDyneSystems]

At the top of this forum.. there is a "sticky thread"

It is called -=READ FIRST=- EOS "Sticky" Thread

If you read it first.. you will find this link;

-=CROP FACTOR=- 10,000 posts on the X-Factor (http://photography-on-the.net/forum/showthread.php?t=45388)

Which covers all you ask.. and far far too much more. :wink:


P.S.
David.. that is a brilliant reponse.. thanks for that thorough answer. :)