ISOless sensors, read noise and photography - many questions!

Started 6 months ago | Discussions thread
Elyharbour
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Re: ISOless sensors, read noise and photography - many questions!
In reply to Steen Bay, 6 months ago

Steen Bay wrote:

Elyharbour wrote:

As someone with a science background, but no specific knowledge in the field of electronic imaging, I hesitate to jump in here and ask a question...but here goes.

From what I glean from this and other recent ISO related threads, when I turn up the base ISO value on any camera, beyond a certain point I'm no longer increasing the electronic "gain" "amplification" or whatever it should be called, and further increasing ISO is doing no more than would be achieved by increasing exposure in Lightroom - noise, detail, etc, is going to be approximately the same (forgive my over-simplification, but in essence, that's what I think I'm reading).

If this is the case, then so long as I'm happy with a "dark" photo on the camera screen, I could limit ISO to say 800 or some other value and correct accordingly in PP. But, as this value will vary from camera-to-camera, the only way to find out what it should be, is to try it and compare results. Ie. there is no magic formula we can all apply.

Is this broadly speaking correct?

Yes, that's pretty much it. If you shoot at e.g. ISO 800 instead of ISO 3200 (same f-stop/shutter speed), then you'll get 2 stops more of highlight headroom. That's a nice thing of course, but on the other hand, if you didn't blow important highlights at ISO 3200, then you don't really gain anything.

On sensorgen.info you can get an idea about where your camera becomes 'ISO-less' (the ISO at which the read noise is about as low as it gets), but always a good idea to test it yourself.

http://www.sensorgen.info/ (click on a camera to see more data)

Thank you. So if I look at the Sony NEX-5 for example (which I do have) the read noise curve shows a minimum at 400 but it looks fairly flat, so, it's not going to make a lot of difference in this case (??) Whereas for the Sony A-55 (similar to my A-57) it slopes down more sharply with a minimum at 1600.

BTW, I expected read noise to slope the other way - ie. lower values at lower ISOs. But that's my lack of understanding showing here...

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