Pixel pitch, noise and image quality?

1-After starting another thread on this forum I got really confuse about pixel pitch, pixel size and image quality.
A bigger pixel pitch (distance between the center of each pixel location) is a consequence of bigger pixels or not?
Is it possible that the pixels are of the same size but with a bigger distance between them?

2-Is it better to have a sensor with a bigger pixel pitch? Why?
Because it has less noise? ...and what about resolution?
Bigger pixel pitch means less pixels per square unite, right?

A large part of the pixel pitch is determined by the size of the pixel. As an example lets compare the Sony 8MP sensor in the 828 to the Canon 8MP sensor in the 1DMK2. In the case of the Sony, the 8MP sensor is very small about 1/4 the size linearly of a 35mm frame - this results in a pixel size of only abut 2.5microns. The Canon sensor in the 1DMK2 on the other hand is about 77% or a 35mm frame linearly and can therefore have much larger pixels - over 8 microns. A larger sensor, like a larger aperture will collect light more easily and therefore generate a stronger signal than a smaller sensor. This is why the small sensor digicams usually only have an ISO value of 400 at the high end - since the pixels are so small, they don't collect light as much so going to a higher ISO would require a much stronger boost in the signal and thereby amplifying the digital noise.

So in general, large pixels will usually result in better image quality.

Hope this makes sense.

Alexandre Vaz wrote:A bigger pixel pitch (distance between the center of each pixel location) is a consequence of bigger pixels or not?
Is it possible that the pixels are of the same size but with a bigger distance between them?

Ideally each pixel would take up all the space to its neighbours (and thus be as large as it can be) but unfortunately a bit of space is usually used up with control circuitry.

2-Is it better to have a sensor with a bigger pixel pitch? Why?
Because it has less noise? ...and what about resolution?
Bigger pixel pitch means less pixels per square unite, right?

Yes the bigger pixels typically have less noise (they can gather more light).
Yes the pixel pitch is a linear measurement, and effectively is squared when you start talking about area.

If you compare the smaller sensor (Sony) with the larger (Mk11) at a lower ISO ( 100) would the gap in difference be small or is it still a big difference. I know with some digicams the main issue is the quality of the lens. However the Sony seems to have a good one and the upcoming Canon has L glass.

Alfred

There will be a difference but one that probaly won't be a big deal until you get to larger than 8x10. One way to look at it is that a 2 micron pixel sensor will be two stops less sensitive to light than an 8 micron sensor so an ISO 100 image on the 2 micron pixel sensor will be about equal to ISO 400 on the 8 micron pixel. This of course is a simplification as other factors come into play such as the image processing chip, lens, etc.

E.J. Peiker wrote:One way to look at it is that a 2 micron pixel sensor will be two stops less sensitive to light than an 8 micron sensor

How do you come to this conclusion? Assuming a 100% fill factor, a "2 micron" pixel will have an area of 4 square microns, and an "8 micron" pixel will have an area of 256 square microns. That's a ratio of 64:1, which I think would be more than 2 stops difference in light-gathering capability.

This of course is a simplification

Granted.

Actually an 8 micron pixel is 64 square microns and as you say, a 2 micron pixel as 4 square microns so the real difference would be 4 stops different (4,8,16,32,64) so an ISO100 image on the tiny sensor becomes an ISO 1600 image on the large sensor for the same level of final output size. In other words an 8x10 printed from the P/S at ISO 100 should look about the same as an 8x10 from the DSLR at ISO 1600 - all other things being equal.

Arg. I initially thought 64 and then "corrected" myself. Whoops

I own the Sony 828.

Images at ISO 100 are pretty comparable to ISO 400/800 with a 10D.

Images at ISO 64 are comparable to ISO 400 on a 10D.

OTOH, ISO 100 is less sensitive than ISO 100 on a 10D, about equal to ISO 50 on a 10D.

Fortunately the lens is very fast, f/2 at the wide and f/2.8 at full telephoto.

It's a nice good light travel camera, a very nice macro camera with a good diopter, and an excellent lightweight landscape camera. The movie mode is a great plus, and there is no dust on sensor problem.

The big problem is a tendency to purple fringing, it can be easily removed in photoshop when it appears, but some people can't live with it. Hopefully the next version will rectify this problem.

It's a dreadful low-light camera compared to a dSLR, and useful for wildlife only in good light and short distances. AF is very nice though.

I'll be picking up a dSLR this year, looking at the D70 although the new Minolta with built-in antishake (IS) is what I really want. I may not be able to hold out until this fall though. I suppose I can always sell the D70 at that point.