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| p.4 #9 · MP wise, where's sweet spot on FF sensors... |
People who talk about buckets tend to forget that you can hold just as much water in a lot of smaller buckets as fewer larger buckets. I understand its an analogy, its just one that really doesnt work.
I disagree; I think it's a very good analogy. Most noise is a function of signal-to-noise ratio, which happens at the pixel level, and the amount of light gathered by the entire sensor has little to do with SNR; the amount of light gathered by each sensel does.
Let's say for example that a given sensor generates one photon's-worth of noise at each pixel. Let's then imagine a sensel so small that at -- say -- 1/250 second only 2 photons can get in at a given light level. Small bucket = 2:1 SNR.
Now let's say we have a sensor with the same number of total pixels, but each sensel is larger due to closer spacing (sensel pitch), etc. This one can gather 10 photons in 1/250. It has the same number of buckets, but larger buckets = 10:1 SNR = less noise.
Furthermore, let's look at exposure. Regardless of the number of pixels, each pixel has to be exposed to a certain level to accurately reflect the scene. Smaller sensels, because they gather less light in a given amount of time, would require higher ISO settings at the same shutter speed than a sensor with larger sensels. Again, it's the size of the light-holding buckets that affects exposure, not the number of them. The number affects the fineness of detail that can be recorded, but not the exposure level.
At least that's how I understand it.