Originally posted by dosdan Another point. There is a scientific paper that argues that, in an
ideal imaging system, 1000 is the minimum number of photons per sensel required to get an image without shot noise becoming visible:
Psychophysical thresholds and digital camera sensitivity: the thousand photon limit Quoting: In summary, an ideal single capture camera must be designed to capture 10^3 photons in the dark part of an image to avoid visible photon noise. The pixel must be able to capture 10^6 photons to encode the dynamic range of natural images. These are the basic constraints for an ideal camera that can render the vast majority of natural images with no visible noise and no saturated pixels. For real cameras, the requirement can be even higher due to the addition of electronic noise and color process functions (such as color correction).
So if the sensel in the K-3 has a 30Ke- FWC (I haven't seen the actual value reported by anyone yet, but I suspect it's around 30Ke-), then 1000e-, which would needed for a 33:1 (30dB) SNR, would be 2 stops below ISO12800 i.e. at ISO3200.
BTW, my K-5 calculations indicate that its sensels have a 34:1 (30.5dB) SNR at ISO3200.
Of course, real-life sensors also have read noise, made up of sensor read noise, PGA noise and ADC noise, and images will start looking noisy at lower ISOs.
Dan.
HI DOSDAN
I calculated that the sat point of the K3 at base ISO - 94 (100) the read noise was 3.33, Saturation 24500 and DR 12.84
See
K3 Read Noise, Sat and DR: Photographic Science and Technology Forum: Digital Photography Review for a bit more. QE is fairly high at 48%
The K5 is quite a bit better in its saturation calculated at 47159 from Sensorgen. I used the same method as Sensorgen.
The tradeoff in pixel noise levels on the K3 vs K5 is that we have many more pixels on the K3. So when sized and viewed similarly the apparent noise is similar.
I have the K3 and K5. In most situations its very hard to tell which photo the K3 versus the K5 took. However the resolution difference is quite noticeable.
I find that under 3200 the K3 has better IQ. Above that its about the same due to noise and what I need to do to mitigate it - I lose most of the improvement in resolution to mitigate the noise. Below 1600 and in particular below 800 the I find the K3 is quite a bit better in many ways.
Although I shoot raw mostly I have been quite happy with the default tuning of the JPEGs. Now that I've spent some time tuning the parameters I like them better than my Olympus. And that is saying something.
Jim