[Miguel]

Just to give you a subjective take when comparing a few factors, I'd say that my Canon 7D (18 MP) provides significantly better low light performance than my Pentax K20D at ISO 3200. I'd say the K-7 is about the same; the K-5 and newer are better at higher ISOs. At a certain point the quality of the image is more dependent on your post-processing skills.

M

[THoog]

The K100D Super was the best of the 6MP bodies, but when it comes to low-light performance, my K-x (12MP, CMOS sensor) ran multiple rings around my K100D (6MP CCD) or K-m (10MP CCD, same sensor as K10D and K200D). I'd have to say technology trumps pixel size. The 6MP sensor also had an annoying tendency to "go orange" (oversaturate reds and yellows) and get hot pixels in low light, something the 12MP never did.

[Darley]

That is probably true, though I don't know that the high ISO (3200) performance is that great. What you mostly get over the K200D is the additional stop sensitivity.


Steve

High ISO is not a concern as I intend using longer exposures if necessary, but it's more about the ability of the sensor to distinguish shades of light when the light is dim. I think 'better dynamic range' may be the expression I'm looking for but in low light situations such as in shaded areas (woodland etc) or at night with no natural light sources.

[Darley]

I think we're getting muddled with ISO and noise. It's about the ability to detect low levels of light and reproduce the levels accurately as different tones so that in low light a darker area doesn't just appear black but as a darker shade of grey, if that makes any sense?!

[Darley]

Interesting that CCD and CMOS has been raised - my understanding is CCDs are more sensitive to light. CMOS are just cheaper to make, that's why we see so many of them.

[audiobomber]

The K100D models have shake reduction, the DS doesn't. The K100D Super will focus SDM and DC lenses, and also has dust reduction.

But to go back to the original question, fewer pixels does not mean less noise in the image. The D40 has the same Sony sensor as the DS and K100D models. Here are the directly comparable signal-to-noise ratings from DXOMark:
D40 (DS, K100D), ISO 561
K200D, ISO 561
K-500, ISO 1087

What this means is that at the same resolution, the old 6mp sensor will show the same noise performance as the 10mp K200D. The 16mp K-500 will be cleaner by about one stop. If one already has a K200D, I don't see much point in getting a DS or K100D.

[audiobomber]

I think we're getting muddled with ISO and noise. It's about the ability to detect low levels of light and reproduce the levels accurately as different tones so that in low light a darker area doesn't just appear black but as a darker shade of grey, if that makes any sense?!

Again, newer cameras have better dynamic range than older cameras. You need to look at DXOMark tests, they show what a sensor can do. Click on Measurements, then SNR and Dynamic Range.
Compare cameras side by side - DxOMark

[Darley]

Ah Dan but I'm not talking about noise, I'm talking about light sensitivity. Noise is not an issue. Low noise capability does not mean better sensitivity to low light. Interesting about the Sony sensors, I didn't know that. I think i'm just gonna buy something cheap and see if I can answer my own question because I don't think I'm explaining it well

[Darley]

Ok Dan will look into that DXOMark

[audiobomber]

Ah Dan but I'm not talking about noise, I'm talking about light sensitivity. Noise is not an issue. Low noise capability does not mean better sensitivity to low light. Interesting about the Sony sensors, I didn't know that. I think i'm just gonna buy something cheap and see if I can answer my own question because I don't think I'm explaining it well

People get confused because they zoom right in to view images at pixel level on their computer screen. If you compare 100% crops from a camera that has few pixels with one that has more pixels, the lower resolution files may look cleaner. The K100D and K10D were perfect examples of this. People who were used to the K100D or DS saw more noise when they looked at K10D files, but it's because they were pixel peeping at resolutions the K100D could not display. If samples from both cameras were viewed on a computer screen without downsizing, or printed in sizes below 8x10, the results were very similar.

I can see getting a CCD sensor if you like the warm look they produce and don't need movies (bleh!) or high ISO. But you already have that with the K200D. All you will gain with a K100D is an inferior body and reduced ability to crop. A DS may be of interest to you. At least it has a larger OVF and TTL flash. In those ways it is different than what you have, but in most other ways it is inferior.

Personally, I would start saving for a K-50.

[ScooterMaxi Jim]

Just to clarify a few things. First, pretty much all of the 10 mp sensors were designed for great low ISO performance, and they are quite superior to the 6 mp sensors in that regard. Of course, the older sensors were designed to work best at 200 ISO, so that is a big factor. Most folks feel the 6 mp sensors are nearly a full stop better at ISO 800-1600 (but going above 800 is something you would do only is a dire situation). I agree that the *istD was a great choice for folks who wanted to keep using the old TTL flash system; I still have mine. However, the screen and buffer are terribly small and slow - and that would frustrate anyone coming from one of the newer models.

For strictly low light shooting on the cheap, I think the K100D Super is the best bet - as it was at the end of the 6 mp run - and it seems they got a bit more out of the sensor. Also, it employed early shake reduction (not great but better than none).

Don't take DXOmark too seriously. All the manufacturers employ smoothing at high ISO, few get caught. The smoothing on the Canon 5D was very easy to see (I shot that body for a few years). Even the Pentax 20D sensor had better high ISO performance (but not as good at low ISO). Of course, all the 16 mp sensors in the Pentax cameras outperform the Canon 5D in every respect - especially dynamic range, and especially so from 400 ISO upwards. Full frame on the older cameras were not as good as the newer crop sensors, but it takes field shooting to know that - as opposed to the standard bench tests that get reported.

[Stone G.]

Thanks Boris but is it not a fact that larger pixels can gather more light than smaller ones? Assuming the same physical dimensions, the pixels on a 6MP sensor will be twice the size of those on a 12MP sensor and therefore better able to capture light. That's my understanding anyway!

High ISO is not a concern as I intend using longer exposures if necessary, but it's more about the ability of the sensor to distinguish shades of light when the light is dim. I think 'better dynamic range' may be the expression I'm looking for but in low light situations such as in shaded areas (woodland etc) or at night with no natural light sources.

There are several factors to consider. Given two sensors of equal sizes but different pixel-counts and using the same lens with the same focal lenght and entrance pupil ('absolute aperture') it is true that a pixel on a 6MP sensor will be hit by twice the number of photons that will hit a pixel on a 12 MP sensor. However, the whole sensor will receive identical numbers of photons and your digital image will still be represented by RGB levels between 0 and 255 for each pixel.

Thus, your image will neither be brighter nor dimmer in either case. But the signal-to-statistical-noise ratio will be better with the larger pixels if the sensor material has the same basic sensitivity. The maximum number of photons that an individual pixel can absorp will also be greater for the larger pixel and thus, the large-pixel sensor should have an advantage in respect of dynamic range.

However, sensor technology has developed very rapidly and the above comparison only makes sense if you have sensors of identical base sensitivity ('quantum efficiency') to compare. It is not enough that a pixel (photo diode) is hit by a photon, it must also be captured by that pixel and the efficiency of that capture process has steadily increased over the years.

Further, there has also been advances in respect of the electronic circuits that operate the sensors. Although you are not too concerned about noise, I believe you should be to a certain extent: Older sensors will tend to show amplifier glow much sooner than modern ones during long exposures and the noise level will increase more rapidly with the older sensor electronics.

[jimr-pdx]

I'll bet a modern 6Mpxl sensor would be pretty amazing but with some things you can never go back. I do remember getting some nice iso800 shots with my K100d, but of course the camera didn't even have a setting beyond 1600 or 3200... can't remember which.

[Darley]

There are several factors to consider. Given two sensors of equal sizes but different pixel-counts and using the same lens with the same focal lenght and entrance pupil ('absolute aperture') it is true that a pixel on a 6MP sensor will be hit by twice the number of photons that will hit a pixel on a 12 MP sensor. However, the whole sensor will receive identical numbers of photons and your digital image will still be represented by RGB levels between 0 and 255 for each pixel.

Thus, your image will neither be brighter nor dimmer in either case. But the signal-to-statistical-noise ratio will be better with the larger pixels if the sensor material has the same basic sensitivity. The maximum number of photons that an individual pixel can absorp will also be greater for the larger pixel and thus, the large-pixel sensor should have an advantage in respect of dynamic range.

However, sensor technology has developed very rapidly and the above comparison only makes sense if you have sensors of identical base sensitivity ('quantum efficiency') to compare. It is not enough that a pixel (photo diode) is hit by a photon, it must also be captured by that pixel and the efficiency of that capture process has steadily increased over the years.

Further, there has also been advances in respect of the electronic circuits that operate the sensors. Although you are not too concerned about noise, I believe you should be to a certain extent: Older sensors will tend to show amplifier glow much sooner than modern ones during long exposures and the noise level will increase more rapidly with the older sensor electronics.

Thank you, that goes a long way to answering my question! So would a modern 6MP sensor be better than a 12MP sensor and if so why don't they make them?!

[ScooterMaxi Jim]

I'll bet a modern 6Mpxl sensor would be pretty amazing but with some things you can never go back. I do remember getting some nice iso800 shots with my K100d, but of course the camera didn't even have a setting beyond 1600 or 3200... can't remember which.

My guess is it would look a lot like a crop from the new Nikon Df - or the D4 sensor, as the pixel size would be a close match.

If memory serves, the K100D Super probably was the first to have 3200, the ones prior went only to 1600. You can be pretty sure that it was an artificial expansion - basically a marketing decision.