Assuming that el cuatro has an AFE - yep.
And which Sigma cameras are certainly known to be ISO-less ?
SD9, SD10, SD14, DP1, DP2 and more.
ISO gain is simply a multiplier factor applied in software. Exposure (= amount of light) is the sole determinant of image quality (in the context our discussion).
Why would you set the ISO to 1600 and then over-expose? In low light you should always expose as long as possible (to avoid motion blur), so if you can afford a longer exposure time why not go with ISO 800 from the beginning. Anyway, the ISO is secondary, its only importance is that it tells SPP how much to denoise. It does not change anything in the raw data.
Thank you.
An interesting assertion - quite the opposite of normal photographic practice!
Let me try again: in low light one should expose as long as possible (while avoiding, or minimizing, motion blur).
It simplifies life, yes. And if the sensor has very low noise it also improves the image.
Not necessarily. If you shoot at, say, ISO 400 and expose properly you can set the gain to 4x and you won't clip. But if you overexpose or use a gain > 1 at ISO 100 you will clip.
I'm confused. How does a User "set the gain to 4X" in, for example, a Quattro?
So - I have to be more precise then
OK. But when shooting at high ISO you don't really worry about clipping, and the analog amplifier is beneficial, because it will reduce the ADC quantization noise.
By setting ISO=400 in the camera--it's automatic.
Setting the ISO to > 100 will do that.
Why? Why cannot high ISO images have high contrast?
Yes, but if the sensor is very noisy (like the Foveon is) then you do not gain so much.
I did some initial measurements of AFE for Quattro. The amplification is not linear with ISO, it increases more slowly. I plan to do more accurate measurements when I get time.
The quoted statement is either too general or it is over-simplified - whichever applies. If, for example, I owned a SD15, I would be very worried about clipping (assuming that the worthy member is referring to ADC clipping).
I am a little amazed where discussions leads.
High dynamic range? Sure they can. But there are at least 2 reasons to use high ISO: low light scenes and fast moving objects. Not sure that in such cases you worry about some blown highlights (like the lights in a dark bar)
