I suppose I should join a photography forum but I know there are some very knowledgeable people on here.

I've got 3 Nikon camera bodies. Two DX format - D40 and D90 and one FX format - D700.

When I take photographs in average to good light the photographs are virtually indistinguishable in quality - no matter whether I am using a cheap and cheerful lens or a high quality one.

However in poor light things change a lot. The D700 is excellent and I understand why. What I don't understand is why the D40 is quite close to it. The D90 trails behind.

The only thing I can think is that the D40 has only 6MP compared to the D90 with 12MP. Therefore it seems to me that the same glass is not dividing up the light per pixel to the same extent. Does this make sense? If this is the case then is there a general penalty to pay for more MPs in DSLRs - especially when we don't change the sensor size?

Malcolm

I only own 1 dslr body, a D50 but it could be that the higher pixel count see's more of the lower end of the light spectrum. Are you manually setting the white balance on each camera ?

It could be caused by noise during processing, the higher the pixel count the lower the light reaching each pixel, so the reading from each pixel has to be amplified more, which also amplifies the noise. Higher MP doesn't necessarily mean better pictures, especially in the cheap cameras where the processor just isn't up to it making it slow to use as well.

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This is exactly the sort of thing the Cap'n ponders as he drifts off to sleep Me? I count hot little vixens wearing rubber jumpsuits jumping over my garden wall and chasing me into my bedroom, sorry, I mean I'm inclined to go with Darren's theory of less light per pixel.

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Fly Clips & Stands

Aye true rob, now we must enter into the size of each pixel??? Its getting complicated...

As in everything there has to be a trade off. Its all about collecting the available photons of light. Larger pixels collect more light than smaller ones but the resolution suffers.
The term you are looking for is the Modulation Transfer Function and each will have its own graph of values.

are the physical dimensions of the cmos chips the same in each body..

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Oh lord give me back my polaroid instamatic camera

Icky Pimp.

I know the sensor sizes in the D40(6MP) and D90(12MP) are the same 370mm2

- many times the size of a compact. The D700 (864mm2)is much larger again.

P.S. does anyone know how to put in superscript in this PHP editor - I wanted to put in the "squared" symbol above?

Easiest way is to just use C&P from the Windows Character Map Endrick. To access it go to 'Start' > 'All Programs' > 'System Tools' > 'Character Map' and just select the one you want.

Like so ²