More Pixel Density

Started Jul 28, 2008 | Discussions thread
OP John Sheehy Forum Pro • Posts: 21,582
Re: Thank You

Tlon wrote:

I've been following your recent threads re. pixel density with great
interest. I'd just like to thank you for taking the time to actually
test a very common assumption, sometimes facing inappropriate (to say
the least) language and baffling misunderstanding.

I have two questions, though:
1. How about lens resolution? How small can the pixels become before
the lens prevents further improvement in IQ?

That depends on the lens and how it is used. A good macro at f/2.8 could easily use 50x the pixel density of a kit lens wide open or at f/32. For some reason, people seem to be obsessed with the lowest common denominator.

If we had 200MP cameras, the cameras could be designed so that a user option forces lower output resolution or JPEG-like compression on severely over-sampled RAW captures.

2. The current thread shows a slight advantage for large pixels at
high ISO, while the previous ones showed advantage for small pixels
at low (although pushed) ISO.

If we're looking for noise itself, it is easier to find in the FZ50 image, because it's pixel read noise times the pixel pitch is higher than the 400D's, and because there is more pattern (line) noise in the FZ50. It is also easier to find detail in the FZ50 image, though, so I can't really say I'd prefer the 400D output here. The pattern noise doesn't have to be there to the extent that it is, and if I had used the G9, I think we'd see a bit less of the red streaks. I just continued with the FZ50 so I wouldn't be accused of trickery.

Can you explain when large pixels will
be better and when they will be worse?

Many CMOS sensors (complex ones; not the simple implementations used in cameras like the D2X) have lower read noise relative to absolute signal at the higher ISO. It is highest at base ISO, drops very rapidly for about two stops higher ISO, and then starts leveling off and completely levels off when the non-gain ISO are reached (usually the top one or two ISOs on DSLRs). The small sensors in compacts and bridge cameras do not have the required circuitry to do this, so noise, relative to absolute signal, is usually very close at all ISOs.

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