Question on ISO performance of K20d or K7

2techsans · 07-03-2009, 04:50 PM

I'm considering upgrading from my k100d and had a question in regards to ISO performance...

If one selects a lower quality rating than the full 14.6 megapixels does it improve the effective noise at higher ISOs? In other words, if one was happy with ISO 1600 performance and dropped from 14 to 7 megapixel performance (which might be great for some situations), would I gain a stop or two in ISO performance?

It seems people want full frame for lower noise; is going to lower megapixels setting on the existing chip have a similar effect?

*Ash* · 07-03-2009, 05:20 PM

Lowering pixel count doesn't give you an extra 'boost' in ISO performance - it just means that the existing (same) noise will be smaller and thus less noticeable.

FF vs APS-C is a different argument with regards to ISO performance - it's not just about pixel count - more to do with the combination of signal to noise ratio and number, size and density of photosites on the sensor, as well as the type of sensor system and camera noise reduction software...

*falconeye* · 07-03-2009, 06:34 PM

- Reducing the pixel count reduces the pixel noise (as measured in dumb test reports), but not the image noise (how the image would look when printed).
Going to 1/4 of pixels (1/2 of size) is like going to SQRT(1/4)=1/2 of ISO. This is why posting noise samples in web resolution is so useless...

- Increasing the sensor surface captures more photons and decreases the image noise. But only if you compare at the same f-stop.