ISOless sensors, read noise and photography - many questions!

Started Oct 3, 2013 | Discussions thread
EinsteinsGhost Forum Pro • Posts: 11,977
Re: in one sense, pointless to use ISO above 800 on Nex C3

RussellInCincinnati wrote:

OK Alan, have put the time in studying the sensorgen site. IF you don't get color casts/banding during your raw post-processing brightening, it appears that there is no point in ever manually setting a Nex C3 to above ISO 800. Because if you do, you are just amplifying "the noise" as much as the brightness and not really getting anything that you couldn't get in post-processing with a lot more finesse and options. Will be checking this out, the practicality of staying at ISO 800, at least with Lightroom 4.4 for Windows if not RawTherapee and LightZone (i.e. latest dcRaw).

Said another way, you might as well brighten a C3 raw digitally, at your leisure if there's not enough light for ISO 800. Just let the raw file "look superficially dark" and figure you'll brighten it in post-processing.

Of course one downside of not setting ISOs above 800, just underexposing, is that you don't get a nice review of the image in-camera, it will always look grim in the playback menu.

I would normally use the post adjustment within limits, 2 stops at the most. If noise is an issue, the idea should be to expose (even slightly) to the right at any ISO. The benefit with shooting at a fixed, low ISO, as opposed to higher ISO is primarily to utilize dynamic range. Per sensorgen, the read noise on NEX-C3, for example, is at its lowest at ISO 12,800 (practically the same at 800) but 12,800 won't get the results that 800 would. Conversely, I won't be surprised if you used ISO 800 and pushed 4-stop during RAW conversion, that you will notice banding and color issues.

I rarely see situations where meaningful images require ISO 6400, that I would set ISO 800 and push 3-stops later. But, I do see 1600 and rarely, 3200, as needed. In those cases, ISO 800 and 1-2 stop push suffices. Here is a result from a trial run a while ago (NEX-3, LA-EA2, Minolta 200mm f/2.8G):

f/2.8, 1/640s, ISO 800 (+1-stop during RAW conversion)

Typically, NBA games require ISO 1600-2000 for 1/500s or faster shutter speeds with f/2.8.

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