Originally posted by clackers All of the light that was falling on the 100mmx100mm sensor is not now concentrated on the 50x50 sensor.
Incorrect.
When I asked you
"Do you agree that the exposure (light / area) is different between the 50mmx50mm sensor and the 100mmx100mm sensor?, I explained that both sensors receive the same amount of light.
Do you accept that "focal length" and "registration distance" are not the same?
If you do then can you imagine the same scene being captured with two cameras that use different registration distances?
Can you now imagine that the lens on the camera with the larger registration distance will produce an image circle that is larger and further away from the mount?
Can you finally imagine that both image circles contain the same amount of light but that of course the intensity of light in the larger image circle will be lower?
If you followed me so far, how can you not agree that the exposure (light / mm^2) of the larger image circle is lower?
Originally posted by clackers Only half of it is.
You are obviously thinking about a "cropping" situation, i.e., only changing the sensor size, but not the size of the image circle at the same time.
My example was different, but let's assume your cropping scenario.
Do you realise that the surface area of a 100mm x 100m sensor is four times larger than that of a 50mm x 50mm sensor?
Why would still "half" of the light be captured by the 50mm x 50mm sensor?
If we had a cropping situation -- which we had not in the thought experiment I described -- then only one quarter of the light (not one half) would be captured by the smaller sensor.
Originally posted by clackers Richard Butler ... clearly cannot control variables, since he uses four different cameras and lenses for his DPR 'experiment' you obsess over)...
Can you please explain to me what exact variables he fails to control?
He has to use different lenses, not only because different mounts are involved but because he needs different focal lengths for the different sensor sizes. While that may influence bokeh, CA, etc. these are image aspects we are not interested in here, as the focus is on image quality as determined by noise levels.
Obviously he has to use different cameras to compare different sensor sizes.
Can you please furthermore explain why the variables he did not control (e.g., camera brand) would invalidate the experiment?
Note that Richard Butler explicitly mentions "sensor performance" and "differences in transmission between lenses" as important factors that influence results, so he is aware of these threads to validity. So what did he do wrong, exactly?