d shay Posted May 25, 2022 Share Posted May 25, 2022 59 minutes ago, HockeyFan12 said: I have a very limited understanding of sensor design, but highlight dynamic range should be dictated by full well capacity. Each photosite is like a bucket. It can only fill with so many photons before it overflows. The reason most of these current cameras are 500-800 base ISO is because they need to underexpose and dig into the shadows to distribute DR since the photosites are only so big and can only hold so much light before being saturated. I suspect when the S1H shoots 640 ISO in V Log, the sensor is reading out the same signal as 100 ISO in another picture style. It's just digitally redistributing the dynamic range into the highlights. The Alexa has about half as many pixels per square inch as the C200 (4K S35), S1H (4K in S35), Venice (4K in S35), etc. Its photosites are about half as big. (2880X1620 = 4665600 photosites; 4096*2304 = 9437184 photosites) So they should hold twice as much light (one stop) before overflowing. Unsurprisingly, the Alexa has about a stop more highlight dynamic range than its competitors at base ISO. The Alexa35, however, has pixels that are about the same size as the C200, S1H, Venice, etc. But it has 1.5 stops MORE highlight dynamic range than the Alexa Classic. So that's 2.5 stops more than the competition. Maybe the base ISO of the Alexa35 will be 1600 to account for some of that (it underexposes and pushes an additional stop)? And the sensor design has physical improvements that account for the rest? Regardless, this puts the camera on another level from everything else on the market. But if its base ISO is 1600 that might explain it to an extent. Or maybe I misunderstand this and there are other factors like voltage involved? Regardless, this camera has already far surpassed my expectations. You are missing a step. The problem with photodiodes isn't that they are too easily filled up and clipped, but that the signal is too weak and needs to be boosted. The clipping occurs when the a/d convertor cannot handle the boosted photodiode signal. Dual gain sensors get around this by having a regular boosted channel and a second path with little to no boosting(highlights). These two paths are then combined to get a single image. The signal to noise ratio of the photodiode plus boost is increased by the difference in signal strength between the low and high boost channels. webrunner5 1 Quote Link to comment Share on other sites More sharing options...
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