FF vs APS-C: Why does FF have lower pixel density than APS-C?

[Robsphoto]

The full frame Sony A900 has a pixel density of 2.9 megapixels per square centimetre, and the full frame Canon 5D Mark II has 2.4. This is lower, for example, than the pixel densities (in mp per sq cm) of several APS-C cameras, such as, the Sony A700: (3.3) the Sony A550: (3.9) the Sony A380: (3.8) and the Canon 7D (5.4).

As an example, a detailed comparison of the mathematical relationships between image size, pixel density, and pixel size of the Sony A900 and the Sony A380 is made here:

http://www.robsphotography.co.nz/crop-factor-advantage-a380-a900.html

It’s an interesting fact that, if the A900 had the same pixel density as the A380, it would have nearly 33 megapixels. But, if the A900 and the Canon 5D II had the same pixel density as the new APS-C 18 megapixel Canon 7D, they would have nearly 47 megapixels:

http://www.robsphotography.co.nz/crop-factor-advantage-7D-5DII.html

So, why are full frame cameras being manufactured with much lower pixel densities than APS-C cameras? Is it because the FF cameras are regarded as “top of the line” and must have the best possible image quality?

Regards
Rob

 

[Cetonid]

Not sure, but I'll bet a factor is that the more photosites on a substrate, the more chance for a bad chip and yields would be worse the denser you get. That said, with the preliminary IQ and high ISO of the A550 sensor, a 33MP full frame would be sweet indeed. My guess is that lens resolution would be the limiting factor once you hit around 40MPon FF.
--

 

[Greenspan]

Err well it makes sense that it would be harder to build a bigger sensor. It's probably harder to keep the same pixel density for larger sensors. It's a cost vs. benefit, how much does it cost to go from 24 MP to 33 MP and how much are people willing to pay for those extra 9 MP?

Something tells me the cost outweighs the benifits otherwise everyone would be running around with 33 MP sensors.

I don't know anything about sensor technologyl, but I trust the forces of free market competition provide a reason.

 

[Dennis]

Some of it is probably difficulty keeping those pixel densities in bigger chips.

Some of it is probably based on market wants/needs. 24MP lets you print huge already; 33MP (or more) gives you bigger files to deal with, more data for the camera to record and process (slowing down the camera) and how many people (who aren't shooting medium format) need to print bigger (with more detail) than 24MP allows ?

Finally, you have diminishing returns because lenses are only so good. You can increase pixel densities and at some point, the increase in captured detail (even with very good lenses) grows much more slowly than the increase in pixel density. The Canon 7D is already said to be limited by most lenses and we know it's possible to build sharper, contrastier lenses for smaller image circles; I don't know if the best FF lenses would exploit a 40+ MP sensor.

All that said, I'm sure 30 & 40MP FF cameras will come in time

• Dennis

--
Gallery at http://kingofthebeasts.smugmug.com

 

[OldScotch]

I suspect it's more to do with processing capability and data transmission. The D3x in 14-bit mode can't maintain 5 fps for example, but it's ok in 12 bit mode. And that's the no holds barred $8,000 supermachine.

 

[lloyd007]

1. Lower pixel densities allow (in theory and in practice) better noise profiles as iso goes up... This is probably the least compelling reason for the A900/850 and it's FF mp competitors but much more so for the 5D, D700 and D3...

2. Yields for FF sensors are much lower and a higher MP chip probably becomes exponentially more expensive with current manufacturing techs...

3. 33mp files = huge... My Core2 system already has heart attacks trying to convert RAWs into highest quality .tiff... A 33mp file is almost adding an a200's sensor worth of data into the file.

4. In camera processing... There's gonna be a big tradeoff in speed of cameras as sensor become larger in MP... MF backs are slow because of this. It's not like we can just jam an Intel i7 965 with 6 GB of ram in a dslr camera body... yet...

5. Lenses can only be so sharp even a technically near perfect lens can only resolve so much be it due to camera shake... slow shutter speed... atmospheric conditions... Sure there is oversampling and the like to consider but honestly that can be corrected in hardware or software...

6. Finally there are practical limits... I've enjoyed my A900... I also enjoy using the Olympsu E-510 / 330 which give me great IQ even up to 16x20 and above but once you start cropping things start to get hairier while the A900 gives me much more latitude to crop and do things like create one image panoramas by lopping off the bottom and top 1/4's or 1/3rds and I'm still left with 8 or more MP of data... But for my purposes the A900 suits me fine... I wouldn't complain if they made a 33mp or 40+ mp or whatever camera but realistically I wouldn't need it...

 

[Robsphoto]

Thanks very much for your interesting replies, there are certainly a number of different “interlocking” issues, which could mean that 40mp on a full frame sensor may be a little way off yet! It’s been mentioned that, realistically, people aren’t going to need 33mp or 40mp, because they really can’t use this sort of resolution!

To me, one of the great advantages of a high megapixel count is the ability to crop and still have enough megapixels left to obtain, say, a 20 inch wide print. I have given examples of this here:

http://www.robsphotography.co.nz/Sony-A900.html

The ability to substantially crop an image and still get a large print from it, means that, even if you use only a 300mm tele lens, after cropping the middle out of a 300mm image, this can give you the same field of view that you would get from, say, an uncropped image from a 600mm lens. So, if we could get to 40mp on a full frame sensor, and if the lens was up to the task, by cropping, you can get the effect of a huge tele lens without actually having to buy one and lug it around! For this reason, I think a lot of photographers would welcome a 40mp full frame camera.

Regards
Rob

 

[Mike Logan]

The crop is what aloes flexibility.





Same shot cropped. A900 cz24-70. God bless America!

 

[ThinCat]

The ability to substantially crop an image and still get a large print from it, means that, even if you use only a 300mm tele lens, after cropping the middle out of a 300mm image, this can give you the same field of view that you would get from, say, an uncropped image from a 600mm lens. So, if we could get to 40mp on a full frame sensor, and if the lens was up to the task, by cropping, you can get the effect of a huge tele lens without actually having to buy one and lug it around! For this reason, I think a lot of photographers would welcome a 40mp full frame camera.

If you crop a 300mm shot to the AOV of a 600mm lens you'd end up with only 10Mp. Is that really enough nowadays? Maybe. Certainly with a high quality modern lens and a high resolution sensor the need for extreme telephoto lenses seems to be diminishing - except for professionals of course.

 

[Kenneth Daves]

Forgive my ignorance, but I thought that the advantage of full frame is in having larger pixels (or photodiodes or whatever the proper term is) that are less densely packed, which makes for better color with less noise. Otherwise, wouldn't a 12MP P&S be as good a choice as a 12MP full frame D-SLR?
--
Ken Daves

 

[David Haslam]

Even in APS cameras the pixel density seems to be set to match competitors rather than than produce optimum results. However the manufacturing process for high density sensors is so good now, it has to be for the mini sensors, that they can produce them easily.

Full frame for a DSLR has advantages other than sensor size. The viewing screen is larger and it uses the full designed coverage of 35mm lenses. If it wasn't for these two factors I don't think full frame would be that important.

--
dhaslam
http://www.pbase.com/dhaslam/galleries

 

[ThinCat]

Forgive my ignorance, but I thought that the advantage of full frame is in having larger pixels (or photodiodes or whatever the proper term is) that are less densely packed, which makes for better color with less noise. Otherwise, wouldn't a 12MP P&S be as good a choice as a 12MP full frame D-SLR?

I think the point of the question is that, if lower density is better for FF, then why don't they make the APS cameras lower density too - provided that there are enough pixels to provide a large enough print, etc. Why is the Canon 7D 18Mp (or whatever it is) when 12Mp (or less) is enough? Why will the A700 successor probably be more than 12Mp? Why are the P&S cameras involved in such a crazy pixel race when their main problem is noise.

I guess the reason is, as has been pointed out, that bigger files are more difficult to handle (especially for the camera cpu) and that the sensors are more expensive to make. I reckon the Nikon D3 showed the way to go with a 12Mp sensor and stonking high ISO performance. It would be nice if the new A700 followed this approach and had 10Mp (or certainly no more than 12Mp) and used the advances in sensor design to deliver really usable ISO1600.

 

[Robsphoto]

The ability to substantially crop an image and still get a large print from it, means that, even if you use only a 300mm tele lens, after cropping the middle out of a 300mm image, this can give you the same field of view that you would get from, say, an uncropped image from a 600mm lens. So, if we could get to 40mp on a full frame sensor, and if the lens was up to the task, by cropping, you can get the effect of a huge tele lens without actually having to buy one and lug it around! For this reason, I think a lot of photographers would welcome a 40mp full frame camera.

If you crop a 300mm shot to the AOV of a 600mm lens you'd end up with only 10Mp. Is that really enough nowadays? Maybe. Certainly with a high quality modern lens and a high resolution sensor the need for extreme telephoto lenses seems to be diminishing - except for professionals of course.

As an example, you could have a look at the images on this page:

http://www.robsphotography.co.nz/Sumatran-Tiger.html

The first Sony A900 image on the above page is a crop of an image taken with a 300mm lens, which originally had an image size of 6048 pixels x 4032 pixels. The cropped image has an image size of 3024 pixels x 2016 pixels, which is exactly half the width and height of the original image. Perhaps a “mathematician” could confirm whether or not the field of view of the cropped image is equivalent to taking the image with a 600mm lens?

If this image is printed at 150 pixels per inch, it will give a print size of 20.16 inches x 13.44 inches. So, although this cropped image has only about 6 megapixels, it has provided a good 20 inch wide print from an image that is only half the width and height of the original. If, in the future, a FF camera has 40 megapixels, you would probably get a good 26 inch wide print from a similarly cropped image.

Although I realise that it’s better to use uncropped images whenever you can, an important benefit of a FF camera is that, if you do crop an image to get in closer to the subject, you can still get a reasonable sized print from even a substantially cropped image.

Regards
Rob
http://www.robsphotography.co.nz/Sony-A900.html
Examples of crops made from A900 images

 

[Robsphoto]

Forgive my ignorance, but I thought that the advantage of full frame is in having larger pixels (or photodiodes or whatever the proper term is) that are less densely packed, which makes for better color with less noise. Otherwise, wouldn't a 12MP P&S be as good a choice as a 12MP full frame D-SLR?

I think the point of the question is that, if lower density is better for FF, then why don't they make the APS cameras lower density too - provided that there are enough pixels to provide a large enough print, etc. Why is the Canon 7D 18Mp (or whatever it is) when 12Mp (or less) is enough? Why will the A700 successor probably be more than 12Mp? Why are the P&S cameras involved in such a crazy pixel race when their main problem is noise.

I guess the reason is, as has been pointed out, that bigger files are more difficult to handle (especially for the camera cpu) and that the sensors are more expensive to make. I reckon the Nikon D3 showed the way to go with a 12Mp sensor and stonking high ISO performance. It would be nice if the new A700 followed this approach and had 10Mp (or certainly no more than 12Mp) and used the advances in sensor design to deliver really usable ISO1600.

Yes, I would agree with your summary. It seems that a few camera buyers assume that, because the Sony A900 has 24.6 megapixels, it must have smaller, and more densely packed pixels than a 14 megapixel APS-C camera. It comes as a surprise to some people to learn that, because of the larger size of a full frame sensor, the pixels on the Sony A900 full frame camera are actually larger and less densely packed on to the sensor than many of the APS-C cameras, such as the Sony A700, A550, A380, and the new Canon 7D.

So, if it’s clear that larger pixels / photosites produce better pictures, why does the new 18mp Canon 7D, for example, have a pixel density as high as 5.4 megapixels per square centimetre, in comparison with the 2.4 mp/sq.cm. of the Canon 5DII and the 2.9 mp/sq.cm of the Sony A900?

http://www.robsphotography.co.nz/crop-factor-advantage-7D-5DII.html

One answer to this may be that recent advances in sensor technology now permit a higher pixel density without a corresponding loss in image quality. For example, the DPR preview of the Canon 7D mentions that:

“The EOS 7D sports a new 18 MP APS-C CMOS sensor which is an in-house development. Canon claims the sensor delivers an improved signal to noise ratio which is achieved through a new photodiode and microlens design. The EOS 7D's sensor features the gapless microlenses that we first saw on the EOS 50D but on the new model the distance between microlenses and photodiodes has been reduced which results in the light being more easily focused onto the photodiode.”

http://www.dpreview.com/previews/canoneos7d/page3.asp

Therefore, the question is, if this new technology can be successfully applied to an APS-C camera, will we see it in new FF cameras, with a corresponding increase in the megapixel count of such cameras?

Regards
Rob
http://www.robsphotography.co.nz