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As I understand, a bigger photosite (on the sensor) enables a bigger dynamic range and also better high ISO performance. Is there a reason not to make the photosite deeper?

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Making the photosite itself deeper actually just reduces the low light performance as it make it so that less of the light can reach the photosite (thus decreasing how dark the scene can be before noise is a problem, but also decreasing the amount of light that gets to the sensor when it is bright, so the entire range of the camera simply shifts to brighter, but no gain in range occurs. The photosites actually need to have a wider range.

  • +1 and a side note: iirc the why is because photo detectors only work at their surface. Film, which may be what Itay is taking inspiration for this question from, does have depth but that doesn't apply here. – Patrick Hughes Jun 5 '14 at 7:37
  • @PatrickHughes actually, the why is that photodetectors don't work at their surface, they work closer to their back, or perhaps the mid. There is generally several layers of filters that process the light before it reaches the actual sensitive layer. (AA filter, bayer color filters, etc). The deeper you stack them, the longer the tunnel the light has to make it through and the less angles light can get in from. – AJ Henderson Jun 5 '14 at 7:42
  • Very true, I was thinking of the actual light sensitive part. Your description of the entire stack makes more sense for this question =) – Patrick Hughes Jun 7 '14 at 3:47

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