DSLR crop factor

OK...so I understand the 1.6 or 1.3 crop factor, however, when someone says that their lens becomes effectively a 112mm (70mm) on a 1.6 is this really true?

You still have the same image that you would have had with a FF only cropped, you have not zoomed in at 112mm have you? And when you then print the cropped image in a format that would be typical to FF, are you really only enlarging it by expanding the cropped image to i.e. 4 x 6, with the associated increase in noise (grain) that you would get by blowing an image up to a larger size?

Crop factor is the result of the fact that the sensor is not as big as the image circle from a 35mm lens. It "crops" out the center of the image. The lens does not change focal length, but the "effect" is that the image looks like a longer lens was used to take it.

DarenM wrote in post #8238175
OK...so I understand the 1.6 or 1.3 crop factor, however, when someone says that their lens becomes effectively a 112mm (70mm) on a 1.6 is this really true?

NO.

What is true is that the field (angle) of view of a 70mm lens used on an APS-C DSLR is the same as field (angle) of view of a 112mm lens used on a 35mm film camera (or a so-called "full-frame" DSLR).

The term "35mm equivalent focal length" is often used to describe the field (angle) of view of a given focal length on a particular camera - even a point-n-shoot camera - relative to a particular focal length used on a 35mm film camera. Manufacturers of small consumer cameras use the 35mm film format as a reference (thus the "35mm equivalent focal length" which they publish) because its an easy way for many folks to compare lenses on point-n-shoot cameras which have different size film frames or digital sensors

The fact is that the 35mm film format (24mm by 36mm) is not, never has been, and never will be the standard camera format against which all others are measured. Even though the manufacturers of small cameras often use the "35mm equivalent focal length" in their advertising, that does not make the 35mm film format enough of a standard to say that a focal length used on some other format is "effectively" anything other than the focal length it actually is.

DarenM wrote in post #8238175
You still have the same image that you would have had with a FF only cropped, you have not zoomed in at 112mm have you? And when you then print the cropped image in a format that would be typical to FF, are you really only enlarging it by expanding the cropped image to i.e. 4 x 6, with the associated increase in noise (grain) that you would get by blowing an image up to a larger size?

The part of your quote that I put in bold type is not correct. If you were dealing with film, it might be correct. However, you are very unlikely to see any image quality (such as the noise/grain you mention) differences - at reasonable print sizes - between images made with today's APS-C format DSLRs and those made with a so-called "full-frame" format DSLR.

rral22 wrote in post #8238244
Crop factor is the result of the fact that the sensor is not as big as the image circle from a 35mm lens. It "crops" out the center of the image. The lens does not change focal length, but the "effect" is that the image looks like a longer lens was used to take it.

.... ONLY if you are comparing two different format cameras using the same focal length lens.

rral22 wrote in post #8238244
Crop factor is the result of the fact that the sensor is not as big as the image circle from a 35mm lens. It "crops" out the center of the image. The lens does not change focal length, but the "effect" is that the image looks like a longer lens was used to take it.

If this were true, would you not get the compression of the image that would happen if it were a true "zoom" from 70mm to 112mm? So you are really not getting the "effect" that a longer lens was used?

SkipD wrote in post #8238283
NO. The part of your quote that I put in bold type is not correct. If you were dealing with film, it might be correct. However, you are very unlikely to see any image quality (such as the noise/grain you mention) differences - at reasonable print sizes - between images made with today's APS-C format DSLRs and those made with a so-called "full-frame" format DSLR.

I realize that there you are "unlikely to see any image quality difference", I guess the point that I was trying to make, was you were actually taking the center cropped area and basically enlarging starting from that center area when you print, rather than enlarging from the area that a ff might cover.

Thanks for all the comments, sounds like I was on the correct line of thought.

SkipD wrote in post #8238283
NO.

What is true is that the field (angle) of view of a 70mm lens used on an APS-C DSLR is the same as field (angle) of view of a 112mm lens used on a 35mm film camera (or a so-called "full-frame" DSLR).

The term "35mm equivalent focal length" is often used to describe the field (angle) of view of a given focal length on a particular camera - even a point-n-shoot camera - relative to a particular focal length used on a 35mm film camera. Manufacturers of small consumer cameras use the 35mm film format as a reference (thus the "35mm equivalent focal length" which they publish) because its an easy way for many folks to compare lenses on point-n-shoot cameras which have different size film frames or digital sensors

The fact is that the 35mm film format (24mm by 36mm) is not, never has been, and never will be the standard camera format against which all others are measured. Even though the manufacturers of small cameras often use the "35mm equivalent focal length" in their advertising, that does not make the 35mm film format enough of a standard to say that a focal length used on some other format is "effectively" anything other than the focal length it actually is.

The part of your quote that I put in bold type is not correct. If you were dealing with film, it might be correct. However, you are very unlikely to see any image quality (such as the noise/grain you mention) differences - at reasonable print sizes - between images made with today's APS-C format DSLRs and those made with a so-called "full-frame" format DSLR.

Skip, I completely agree, but you should have said "NO!!!" instead of merely "NO."

"Crop factor" is a purely marketing term, used to sell cameras and/or lenses. A 50mm lens remains a 50mm lens whether it is used on a 5D (full-frame) or a 40D (APS-C) camera. It NEVER becomes an 80mm lens. Nor does it ever act like one.

However, when mounted on an APS-C camera, a 50mm lens does act like a 50mm lens on an APS-C camera, which is slightly different than a 50mm lens on a full-frame camera. This difference is angular in nature, and affects things angular: angle of view, camera shake, etc.

I can think of no other term that has caused more confusion or, indeed, out and out grief than "crop factor."

How about this: we look up the very first lenticular camera and use its film or plate size, whatever it may have been, as a standard. (After all, it was first.) Then all cameras since can be assigned a relative "crop factor."

That would make more sense than, or at least as much sense as, using the 35mm-film image size as a standard. Hell, the 36×24mm 35mm-film image size isn't even a standard with 35mm film!

DarenM wrote in post #8238766
I realize that there you are "unlikely to see any image quality difference", I guess the point that I was trying to make, was you were actually taking the center cropped area and basically enlarging starting from that center area when you print, rather than enlarging from the area that a ff might cover.

Thanks for all the comments, sounds like I was on the correct line of thought.

The resolution (pixels per unit of length on the sensor) of several Canon APS-C cameras is actually greater than the resolution of the 5D. Thus, you'd have a better resolution image (more pixels) with the APS-C camera than with a cropped image from the 5D. Thus, there's no pat answer to your line of thinking there.

DarenM wrote in post #8238737
If this were true, would you not get the compression of the image that would happen if it were a true "zoom" from 70mm to 112mm? So you are really not getting the "effect" that a longer lens was used?

No lens "compresses" anything in images. Check out our tutorial on Perspective Control in Images - Focal Length or Distance?, as this article proves what I have just said. Many non-believers now understand the truth.

One of you guys should come up with a clear, concise definition that would include FOV and how pixels on target occasionally balances an increased sensor MP value, and etc.
I know the relationships, but the ability to explain it in 25 words or less is...well beyond my capabilities.

that's correct. compression of image is purely based on zoom at different focal length, not crop. youtube hitchcock zoom or dolly zoom.

to illustrate, below is a 35mm adapter for camcorder. it takes a SLR lens and project it to a a ground glass much like the ones in SLR. look at ~4:00, focal length is fixed but the crop factor changes. When Tom G. crops and uncrops the 35mm film-plane, the image stay the same.
http://vimeo.com/98041​9

you do not get the same effect.

DarenM wrote in post #8238737
If this were true, would you not get the compression of the image that would happen if it were a true "zoom" from 70mm to 112mm? So you are really not getting the "effect" that a longer lens was used?

I don't see why there would be a confusion about it. It's fairly simple, maybe coming from video era might have helped the understanding.

that can be said about ISO on SLR and ISO on DSLR. Note that we're in the digital SLR game, things changes and ppl try to retain the standards as much as possible.

20droger wrote in post #8239230
...

I can think of no other term that has caused more confusion or, indeed, out and out grief than "crop factor."

...

That would make more sense than, or at least as much sense as, using the 35mm-film image size as a standard. Hell, the 36×24mm 35mm-film image size isn't even a standard with 35mm film!

Trey T wrote in post #8239391
.... compression of image is purely based on zoom at different focal length....

This is totally incorrect. "Compression" is simply perspective, and perspective is affected purely by relative position between the viewer (or camera) and the subject (or various elements in a scene).

In other words, it's distance(s) and NOT focal length that affects perspective and the so-called "compression" typically attributed to longer focal length lenses.

For proof of the above, please study our tutorial on Perspective Control in Images - Focal Length or Distance?.

since we're speaking about crop factor vs. focal length, I only mention focal length as oppose to crop-factor. but yeah, distance matters too. that's all i am saying.

I am not sure what you wrote, since it's so long. there are a lot of things being done on video that explains what's going on the photography world. below is the example about the view being compressed and non-compressed at different focal length.

http://www.youtube.com​/watch?v=iv41W6iyyGs

that dolly track is prolly about 5' or so.

explanation in a video instead of reading about still photos, much more difficult to understand.
http://www.youtube.com …v=v6-pTX8SQwU&feature=fvw

Crop factor = same reach, reduced FOV in stored image.

The last image in THIS THREAD says it all. There's no perceived distance differential between the subject in the different boxes; you can just see more on the periphery of the interior box.