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| p.4 #12 · MP wise, where's sweet spot on FF sensors... |
RobDickinson wrote: 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.
Then you need to refresh your understanding.
The buckets are equally tall, you just have narrower buckets standing next to each other.
Smaller sensels do not require higher ISO at the same shutter speed.
If you are talking about smaller sensels distrubuted on the same area, they require exactly the same ISO.
If you are talking about a smaller sensor, it requires LOWER ISO to produce an image from the same perspective / subject distance, with the same field of view, the same depth of field and the same shutter speed, because you will use a wider F-stop to get the same physical aperture diameter( and hence DOF) with a shorter lens.