ISOless sensors, read noise and photography - many questions!

Started 6 months ago | Discussions thread
RussellInCincinnati
Senior MemberPosts: 3,186
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on third thought, for Nex C3 raw, this topic not important
In reply to boardsy, 6 months ago

Summary: Am saying more narrowly that doing anything but maximizing your exposure, specifically via using the slowest shutter speed and thus lowest ISO that's practical and doesn't overexpose, for the aperture and scene you've chosen, for almost all practical purposes will not give you any higher-quality raw files, and thus is not worth troubling oneself over--regardless of whether or not a Nex C3 is "ISO-less" or whatever.

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Boring Details

Boardsy, after a couple of days of Nex C3 testing, have concluded that, for C3 raw users, this topic of ISO-less-or-not has no practical value. Because there's nothing wrong with the way the Nex C3 handles the raw data when you set the ISO above 800. I.e. since there's no problematic increase in read noise at ISOs above 800, there's no reason to stay away from those settings.

Wchutt, in this thread, sums up my own advice:

Maximizing exposure at the base ISO, or the...[least]...practical ISO above base ISO, insures you have the best shadow SNR and the best overall dynamic range.

The common-sense idea that the sensor works best when it has as much light to work with as you can get to it (but of course not so much that at your chosen ISO there are important pixels that are real close to the right-hand edge of your C3 exposure histogram), is always true. And you may note that the above run-on sentence makes no mention of whether or not the camera is "ISO-less."

Am not saying that it's uninteresting or dumb or boring to know whether or not a Nex C3 writes different values into it's raw files at various ISO settings for the same manual exposure(which it does, easy to see thanks to Iliah Borg's nice RawDigger program). And I appreciate this thread topic for its educational aspects, for the (in some ways impractical pleasure of) people who just enjoy understanding camera sensor technology and raw file structures.

But am claiming (along with what wchutt implies) that there's nothing practical to be gained by thinking about this topic for a Nex C3 (i.e. whether or not the C3 changes the raw values or doesn't at various ISOs), if you already have the religion of always exposing as much as practical. (Again expose as much as you can without running any important pixels super close to the right-hand edge of your exposure histogram.)

This contradicts my writing yesterday, extolling the virtues of not setting the Nex at ISO 800 no matter how dim the light. While it's true (and interesting to me) that you can limit a Nex C3 to ISO 800 without loss of image quality, no matter how much the scene looks dim because of your too-low ISO setting, my further testing of both too-low and too-high ISO scenes points unmistakeably to there being no point to worrying about your ISO setting in dim light. Because just setting the ISO in dim light to whatever number above 800 lets the scene preview look good is fine--since again there is no read noise penalty for above-800 ISOs.

We might as well just enjoy the nice preview and playback afforded by simply:

selecting whatever lowest ISO lets us capture the scene with the brightest important pixels being just shy of the right-hand edge of the exposure histogram.

Or of course, if the scene is high-key with lots of important highlight detail that you want perfectly rendered, back off exposure so that the brightest pixels in the exposure histogram are maybe 80% of the way to the right. I (and probably you) back off exposure when trying to, say, capture every possible detail in a boring photo of puffy clouds...or more practically, stand off a little farther from the right-hand edge of the histogram when a model is wearing white anything.

By the way, am not saying there are no theoretical differences in what you can get out of a Nex C3 with various too-low raw file ISO settings. But for noticeable purposes am sticking by the statement at the top of this message.

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