ISOless sensors, read noise and photography - many questions!

Started Oct 3, 2013 | Discussions thread
John Sheehy Forum Pro • Posts: 19,971
Re: am happy with your starting this helpful thread

RussellInCincinnati wrote:

Thus the Nex C3 is a good deal of the way towards being Iliah Borg's "true ISO-less camera."

Well, except for Canon DSLRs and some non-Sony sensors used in Nikons like the D4, most cameras with RAW are pretty "ISO-less" by ISO 400 or less.  It would be really nice, however, if the cameras actually used it under the hood, like the Sigmas and many medium format cameras do, or let advanced users decide what gain to use at what ISO settings, and what bit depth the RAW files use.  Shooting an exposure index of 6400 from the camera's ISO 800 gain not only gives you more headroom, but if that headroom is not put to use, lossless-compressed RAWs are smaller, because unlike the least significant bits which are filled with noise, always, the high-order bits contain all or mostly zeros, which can be severely compressed.

Upshot of all this is to make overexposing a low-light photo, or bothering to bracket it, is quaint history.

Well, I have Canons which aren't so-called "ISO-less" until 800 to 3200, but I have always balked at people's suggestions that "proper exposure is very important at high ISOs"; the fact is, the absolute exposure, not the relative exposure at a high ISO, is what determines noise first and foremost.  It seems that many people have trouble distinguishing between relatives and absolutes, and seeing less noise at ISO 3200 with +2/3 EC, and more noise at ISO 3200 and -2/3 EC, they falsely assume that the relative exposure was the thing that made the former better, when, in fact, the only thing that made it better was the 1.33 stops extra absolute exposure, and -1/3 stop at ISO 1600 would give the same noise benefit, and 1 stop more highlight headroom.

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