What is the point of cropped sensors?

[HankW]

What started this? Was it easier to produce these during the beginning of digital cameras? Or is it to hide the imperfections of lenses? I don't see any other reasons to not use a standard that is over a hundred years old. Someone, enlighten me.

[Erik Bien]

The larger a digital sensor is, the fewer of them can fit on a blank silicon wafer, and the more likely they are to have defects: the "yield" of good chips goes down drastically.

Large imagers also require a lot more processing horsepower to record the image, especially if fast frame-rates are part of the requirement (I think most medium-format digital backs are still in the 1-2 fps range). Power draw and heat also increase dramatically.

[Rikki]

Agreed.

What he said ^

[Kin Lau]

There's also the physical process of producing a chip that large... 24mm by 36mm is extremely large in the microprocessor world. Just getting something like that into production is very difficult. There's a nice writeup somewhere showing how much bigger the sensor is compared to anything else.

[tkmslee]

It's simply a smaller sensor...there's really no "point" to get. Referring to the 7D I am assuming that Canon did this for several reasons aimed toward the film maker rather than the photographer. I just got mine yesterday and it is a great film making camera...even the controls have been changed from the 5D and they are really nice.

[Duke]

I think there is actually historical president for it. In S35mm film you can't use the entire frame. You need some space to separate the exposed parts so you know what parts to print without overlaping or bleeding over, and some space on the edge for the sprocket holes, without overlapping.

The APS-C size, is about the size of 35mm film left over that you can actually print. AFAIK, historically the "full frame" was the same film with out leaving safety margins. :hv20-smilie64:

In that case its the FF that's unusual and the S35mm (ASP-c) that's normal (approx. 22mm). Anyone feel free to contradict me. :hv20-smilie84:

[fishops]

In that case its the FF that's unusual and the S35mm (ASP-c) that's normal (approx. 22mm). Anyone feel free to contradict me. :hv20-smilie84:

Ok, guess I'll do it. "Full frame" is normal in 35mm photography film terms, which is why it's the standard plane by which lens focal lengths are still measured. 35mm movie film is smaller because it uses 4 perfs per frame instead of 8, and includes optical audio and sync tracks. Super 35 and APS-C didn't even become popular formats until the mid 1990s.

Digital sensors are generally made as small as possible for the simple reason that the larger they get, the more expensive they are to produce.

[Duke]

All true. My only point was that now APS-C is pretty much the same size as S35 movie film, so APS-C is 'normal' in that regard. Otherwise, there is no normal, and of course there are slight variations in APS-C size.

[fishops]

All true. My only point was that now APS-C is pretty much the same size as S35 movie film, so APS-C is 'normal' in that regard. Otherwise, there is no normal, and of course there are slight variations in APS-C size.

Yeah, I'm not trying to criticize, only clarify. I have to admit I'm curious as to where you heard some of this stuff because it seems a little out there. To address your original post:


I think there is actually historical president for it. In S35mm film you can't use the entire frame.

Actually, Super 35 was invented specifically so that you COULD use the entire frame. The original idea was to use it as a production format, and then optically transfer it back onto theater prints through an anamorphic lens so that you could include the audio track. Due to the extra processing, it never really caught on until digital intermediaries became popular in the mid to late 90s.


The APS-C size, is about the size of 35mm film left over that you can actually print. AFAIK, historically the "full frame" was the same film with out leaving safety margins. :hv20-smilie64:

APS film is only 24mm wide, and was introduced in the late 90s as a cheap, compact format for point and shoots. It has nothing to do with 35mm film at all. 35 is exposed right up to the perfs, there are no "safety margins" that shrink the usable image. The only thing APS-C has in common with 35mm film is the aspect ratio. The the term still exists is because it's astronomically cheaper to make digital sensors in APS-C format. The original APS film formats never really caught on, and aren't made anymore.

[Duke]

Actually, Super 35 was invented specifically so that you COULD use the entire frame.

Sort of. The S35 was made so you could use the part where the optical track would be, its still not as big as full frame.



APS film is only 24mm wide, and was introduced in the late 90s as a cheap, compact format for point and shoots. It has nothing to do with 35mm film at all.

We weren't talking about APS film, we were talking about APS-C sensors. Yes, its cheaper, and easier. IMHO its still relevant because you get the same size focus plane as S35mm movie film.


The only thing APS-C has in common with 35mm film is the aspect ratio.

The usable part of 35mm movie film is almost exactly the same size as the APS-C sensor. S35 projected area is 23.5 x 12.7 for 1:1.85. Right in between Canon's and Nikon's variations.


The the term still exists is because it's astronomically cheaper to make digital sensors in APS-C format. The original APS film formats never really caught on, and aren't made anymore.

I think you mean the chips still exist because they are astronomically cheaper. When I referred to the different sizes, beyond APS-H, the different manufacturers of APS-C make slightly different sizes (Canon at 22.2mm, Nikon at 23.6mm, etc).

Here's a nice little chart:
http://hv20.com/attachment.php?attachmentid=5712&stc=1&d=1256910056

[fishops]

Sort of. The S35 was made so you could use the part where the optical track would be, its still not as big as full frame.

You're mixing up still and motion terminology. S35 is "full frame" for movie cameras.

Movie film runs vertically past the gate at 4 perfs per frame, still film runs horizontally at 8. That is why there's a size difference, it has nothing to do with cropping or margins.

[Duke]

You have to include the terminology when talking about a vDSLR since in essence it is doing both. And yes, I absolutely agree on the orientation of movie file vs. still film.

When 35mm still film is oriented sideways and shot full frame the sproket holes are still the limit in one direction, it takes up more room on down the length of the film, where the borders would be on 35mm movie film. And I have never seen any reference to S35 being full frame. Usually movie film is called academy or Super35.

But what we were talking about was the size of video sensors and it doesn't change the fact that an APS-C sensor is the size of S35mm movie film.

Academy leaves room for the optical sound track and S35 doesn't. Frankly when I used to own a 35mm Eclair you could put different metal frames over the gate for various sized film formats on the same camera.

http://www.studio-x.hu/tiny_mce/plugins/imagemanager/files/cikkek/onephoto_articles/RED_sensor_chart.jpg

[fishops]

But what we were talking about was the size of video sensors and it doesn't change the fact that an APS-C sensor is the size of S35mm movie film.

Not arguing that. Only trying to clear up the earlier nonsense about "safety margins". Your original post seemed to imply that S35 was some sort of cropped format, which isn't true.

[Duke]

True, I could have stated it better. I think the pictures help those with an interest.

[guru]

APS-C does not have anything to do with 35mm film, it's size is similar just by accident. The size of a cropped senzor exists for a few big reasons.

- Significantly lower price of a production comparing to FF sensor
- Additional reach for a photographers that needs it (bird, sports, etc.)
- Better speed of burst shooting and operation (it can work with slower hardware, means price again)
- Opportunity to use lenses with smaller amount of glass, and that means lenses with lower price

[Duke]

Of course, one was developed for film and the other wasn't. The idea of a DSLR for video didn't come along until much later. (As a side note the Red One's sensor is virtually the same size as an APS-C sensor, and it was specifically designed to mimic a film camera.)

On the other hand if you us your APS-C camera for video your lenses will have the same characteristics, same field of view, same depth of field, etc as if you were using your lenses on a S35 movie camera. Plenty of older movie cameras have been modified to specifically use 35mm photography lenses and take advantage of the cheap glass.

It doesn't automatically make your video look like film, but its a start and a very happy coincidence.