More megapixels, better photos: Fact or fiction?

Started Feb 7, 2008 | Discussions thread
John Sheehy Forum Pro • Posts: 25,016
Re: More megapixels, better photos: Fact or fiction?

newsshooterjim wrote:

The article listed pretty well answers the question. The short of it
is that smaller photosites see less light, this means the signal has
to be amplified more in order to get it up to an acceptable level.
Unfortunately, it's just like a tv amplifier. Boost the signal, you
boost the noise. In low light, my 6mp beats my 10mp K10 every time.

The fact is, the more you divide photons into more numerous, smaller photosites, the less image noise you have to create. The smaller the total number of photons that need to be read out of a sensor, the less noise created as measured in photons. The standard deviation of readout noise in a Canon 5D pixel at ISO 100 with up to 53200 photons is about 30 photons. The standard deviation of readout noise in a Panasonic FZ50 at ISO 100, with a maximum of 4800 photons, is about 3.5 photons. A 5D pixel covers about 16x as much area on a sensor as an FZ50 pixel does. So, 16 FZ50 pixels collect about 4800*16 = 76,800 photons. The read noise for this super pixel is 3.5 photons times the square root of 16, or 4. 3.5*4 = 14 photons of noise. So, the 5D pixel has a noise floor a little over a stop higher than the FZ50 "superpixel", and has slightly more shot noise, with somewhat less photon collection. This is reality; not the myth going around that more pixels makes sensors noisier.

One caveat, some manufacturers are finding ways to work around this,
as you can tell if you've seen the high ISO shots from the D3, and to
a lesser extent, the K20.

The D3 has high-ISO optimizations, like Canon DSLRs have always had except for the original 1D (I don't know much about the D30 and D60). The K20D does not have any high-ISO-specific optimizations, most likely. It most likely follows the K10D paradigm of having low universal read noise, and high ISOs just being a different arithmetic manipulation of the same 22-bit readout. Read noise is exactly 16x as strong at ISO 1600 than it is at ISO 100 on the K10D.

The K20D has slightly less noise than the K10D (both are among the lowest of any digital at ISO 100). It won't touch the D3 or the Canons in the high-ISO department, but it will most likely reign in the low-ISO dynamic range department.

A FF sensor with 13-bit RAW and K20D pixel properties (just 2.25x as many of them) would be an awesome camera for low-ISO uses.

Plenty of light, more megapixels is fine, less light, it's a problem.
For me, the bigger problem is the myopic plastic they're passing off
as lenses.

Buy cameras with good glass, always, regardless of MPs. That's one reason why I like my FZ50, even though it takes over 5 seconds to write a RAW and take the next shot, and the Venus NR is not very nice looking on the JPEGs.

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