Is the crop factor the same as digital zoom?

[dlwjiang]

Doesn't a "crop factor" imply a loss of information? Cropping is the same as a digital zoom in a way, and cameras with large sensors usually have more megapixels(though they don't seem to be rigidly related) and a crop on a picture with lots of megapixels would be equivalent to a regular picture taken on a camera with fewer megapixels.

Does this mean that full-frame cameras don't really suffer from "less zoom" (not having a 1.5 multiplication factor) as the same effect can be gotten with a crop? So the 1.5x factor as benefit to aps-c sensors doesn't really exist?

*not sure about all above

[prabbit237]

Originally Posted by dlwjiang

Doesn't a "crop factor" imply a loss of information?

Not in the same sense as when cropping "after the fact." The crop factor mainly affect the lens zoom factor and means that a 50mm lens isn't a 50mm lens any more (rolling eyes at the last part of that statement and not at yer question, BTW.)

When you have a crop factor of 1.5 (where the sensor is (1/1.5)x35mm or 23.3mm in width) it has kinda the same effect as cropping down the picture by a factor of 1.5 but it's also the same as using the same 35mm size sensor and simply zooming in by 1.5. So there's no real "loss" in information, any more (or less) than zooming in "loses" it. If you have a 10MP camera, you still get 10MP worth of information no matter how much you zoom in or out, where-as cropping by a factor of 1.5 would lose some 56% of the information and leave ya with a 4.4MP picture.

But it does mean that if you use a lens from a true 35mm camera on an aps-c camera, you wind up zooming in more with the same length lens. So any lens sizes would need to be multiplied by the crop factor for the true length (and I hadn't even considered that till just now in regards to myself. I have an old 50mm prime lens on a canon rebel so that means it's basically a 75mm or so lens. I haven't used it much cause it's manual focus but it just never registered on me till now about the change in length, even though I knew about the crop factor, etc already.)

One off-topic thing about the sensor size and number of pixels. They are using the standard marketing gimmicks of "More! More! MORE!" and "Smaller! Smaller! SMALLER!" (mainly on point-and-shoot cameras) and packing in more pixels and more zoom into a smaller and smaller package. The more pixels you pack into a given sensor size, the more noise you get (due to quantum effects.) So everything else equal, a 5MP sensor will have less noise than a 10MP sensor of the same size. Also trying to cram 30x worth of optical zoom into a camera means the optics winds up being crap with all sorts of distortion, etc. And digital zoom is really STUPID! All it's doing is taking the picture, cropping it down and then re-enlarging it back to the original number of pixels. That DOES loose information. Better to use only optical zoom and then crop it on a computer if ya really need to zoom in more (and then don't re-size it back up unless ya really, absolutely need to do so to make a larger print.)

===edit===
Correction: my camera has a crop-factor of 1.6 so my "50mm" lens is an 80mm prime and not a 75mm.

[Manouche]

prabbit says it all..

[prabbit237]

Originally Posted by prabbit237

Not in the same sense as when cropping "after the fact." The crop factor mainly affect the lens zoom factor and means that a 50mm lens isn't a 50mm lens any more.

One correction/addition to what I was saying (I realized it may have given the wrong impression.)

When a manufacturer makes a lens for a specific camera and marks the lens as being a 50mm lens or an 18-55mm, those ARE corrected lengths and take the crop factor into account. So my Rebel with the 18-55mm lens will take the same image at the same distance when set at 50mm as a film camera would with that 50mm prime I have. You only need to re-figure lens length when using a lens made for a DIFFERENT crop-factor than what yer camera is (so the 50mm prime was made for a camera with a crop factor of 1/1 and thus I have to adjust when using on my 1/1.6 camera. If I got an adapter and used my EOS 18-55mm lens on a standard 35mm camera, I'd have to adjust in reverse.)

[RLucas]

Originally Posted by prabbit237

One correction/addition to what I was saying (I realized it may have given the wrong impression.)

When a manufacturer makes a lens for a specific camera and marks the lens as being a 50mm lens or an 18-55mm, those ARE corrected lengths and take the crop factor into account.

This still sounds a little misleading. There is no correction to it. 50mm is 50mm no matter what camera it is on. The only difference is the image circle, which affects the field of view, not magnification.

[OsmosisStudios]

Originally Posted by dlwjiang

Doesn't a "crop factor" imply a loss of information?

Yes and no. The sensor itself is smaller, so it only sees a portion of the same scene of a full-frame sensor. If you want to think of it this way, it's like having a window with a smaller window inside it. The DX sensor is the smaller window, the larger window is the FX sensor. You just see a different view. So, you are "losing" the information outside that smaller sensor, but you're getting the same resolution.

Originally Posted by dlwjiang

Cropping is the same as a digital zoom in a way, and cameras with large sensors usually have more megapixels(though they don't seem to be rigidly related) and a crop on a picture with lots of megapixels would be equivalent to a regular picture taken on a camera with fewer megapixels.

This is patently false. Sensor size has nothing to do with megapixel resolution. The D3s and D300s are both 12mp, but the D3s is FX, the D300s is DX. Hell, the current D3100 and D7000 are higher resolution than the D3s, and they're DX bodies. The term "crop factor" is just to give an idea of the field-of-view changes involved, not an actual crop.

Depending on what processing a camera uses, "digital zoom" is either a crop or stretching. Either way, it's bad.

Originally Posted by dlwjiang

Does this mean that full-frame cameras don't really suffer from "less zoom" (not having a 1.5 multiplication factor) as the same effect can be gotten with a crop? So the 1.5x factor as benefit to aps-c sensors doesn't really exist?

Full-frame cameras dont show the same field-of-view as DX (crop sensor) cameras. They show more. So, with the same lens on both bodies, the FX image will show a wider field of view which gives an apparent shorter focal length. It LOOKS like there's less reach.

There's a reason most pros carry both FX and DX bodies: It allows them to have very wide (on FX) or very long (on DX).

[jml79]

Originally Posted by prabbit237

One correction/addition to what I was saying (I realized it may have given the wrong impression.)

When a manufacturer makes a lens for a specific camera and marks the lens as being a 50mm lens or an 18-55mm, those ARE corrected lengths and take the crop factor into account. So my Rebel with the 18-55mm lens will take the same image at the same distance when set at 50mm as a film camera would with that 50mm prime I have.

This is not correct. A 18-55 is an 18-55 no matter what you put it on. On a crop sensor it will have the same field of view as a 28-88 (Canon body). Even if the lens can only be used on a crop body camera the focal length is unchanged. It is still an 18-55 and the same math applies to get your corrected length equivelent compared to 35mm.

To simplify, a lens is a lens no matter what and if you have a crop factor you always do the math (*1.5 or *1.6 or *2) to get your equivelent length no matter what.

[prabbit237]

Originally Posted by jml79

This is not correct. A 18-55 is an 18-55 no matter what you put it on. On a crop sensor it will have the same field of view as a 28-88 (Canon body).

Ok, yer right. I screwed that part up.

[inkista]

Because I like it as an illustration:

Originally Posted by dlwjiang

Doesn't a "crop factor" imply a loss of information?

Yes, but not in the way you're thinking.

What "crop factor" actually implies is narrower field of view, and higher pixel density, but not in fewer pixels. Cropping always means fewer pixels. Digital zoom typically means cropping with uprezing (i.e., resizing to bring the cropped area back to a larger size, with interpolated pixel information). Crop factor cameras can actually have more pixels and a higher resolution than a full-frame camera (e.g., the Nikon D700 is a full frame camera, but only as 12.1 megapixels. A D7000 has 16.2 megapixels, the biggest difference is the size of the individual pixel on the sensor and how that affect high iso noise performance and dynamic range, as well as the field of view the sensors offer).

You also need to know that pixel size/density is not the only factor that determines high iso and dynamic range performance, either (i.e., look at the Pentax K-5 and Nikon D7000 sensors).

Cropping is the same as a digital zoom in a way, and cameras with large sensors usually have more megapixels(though they don't seem to be rigidly related) and a crop on a picture with lots of megapixels would be equivalent to a regular picture taken on a camera with fewer megapixels.

Kinda-sorta, but again, the field of view (and depth of field) issues make it not exactly the same. But your thinking is along the right lines. The difference is that with a crop-body camera, the resolution may be completely different from a full-frame crop that's then been resized, which is what digital zooming is doing.

Resolution tends to be more a function of how recently the camera model was added to the lineup. It's kind of a Moore's Law thing that we keep getting higher and higher megapixel counts as digital cameras progress. They seem to have stopped doing this on P&S cameras, but not on dSLRs.

Does this mean that full-frame cameras don't really suffer from "less zoom" (not having a 1.5 multiplication factor) as the same effect can be gotten with a crop? So the 1.5x factor as benefit to aps-c sensors doesn't really exist?

Depends on how you look at it. Having a wider field of view on a full frame can actually be a benefit if you want to go wide instead of long. And your lenses don't actually change focal length (as everyone's saying).

[dlwjiang]

I think the amount of information that a spot of light focused by the lens has MUCH more information than the sensor can possibly gather is the key here. Two 12 megapixel sensors, if they only differ in size, the smaller one will still be able to fill up its buffer of 12 megapixels of information and so give a picture of the same clarity but at a farther "zoom". (Is there a limit on how much information light itself can give?)

I'm thinking of them as "buckets" now, with megapixels being bucket capacity. Larger sensors take information from a smaller area, with a higher information density in a smaller area, they can essentially "zoom" in on that spot.

Larger sensors, if the megapixels don't change, have to deal with a higher area of information and thus gather "water" from more places, the information density is less.(with "light" being an endless pool of water you couldn't possibly gather up) Once the image is processed, you can't crop out the middle and expect the same clarity as the smaller sensor because you just don't have the same amount of information.

Otherwise "superzooms", which take advantage of small sensors and large lenses, for huge crop factors, wouldn't really make any sense.