ISOless sensors, read noise and photography - many questions!

Started 9 months ago | Discussions thread
RussellInCincinnati
Senior MemberPosts: 3,194
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am happy with your starting this helpful thread
In reply to boardsy, 9 months ago

original poster boardsy wrote: ...if the sensor is effectively ISOless then is base ISO always optimal ...or are you as well off raising it in camera (providing highlights are preserved) rather than in RAW/pp?

Boardsy my takeaway a few weeks ago from our tortuous thread, was to notice that a Nex C3 sensor has minimum read noise at around ISO 800. Which you made so easy to see by including a handy noise graph in your original post.

Now the C3's read noise is not a lot less at ISOs besides 800, but hey why not use the sensor at that most efficient-in-some-ways ISO, even if you theoretically "need" a higher ISO to make the little preview look "good"? Since you can so easily "raise the ISO" (i.e. move an "exposure" slider in say Lightroom) after the fact. The only downside is that the LCD does indeed get dim.

Well have finally brought that concept into the field. In the scene below, the flight was going to be at ISO 3200 and 1/10th of a second. Around F/8 to get complete cross-frame clarity. Everything looked fine in the electronic viewfinder (i.e. clip-on eyepiece-magnified LCD).

But then remembered at the last minute "hey, why sweat the exact exposure when I'm worried about blowing out highlights in the white fabrics? Why worry about how many bracketing exposures needed, at what intervals, just in case? Why not move the ISO back to 800, the screen looks kind of dark but everything's still perfectly viewable/manual focusable, and then can have the luxury of deciding in post-processing exactly how bright to raise the scene highlights? Instead of letting the camera firmware possibly over-amplify the highlight brightnesses in an attempt to make the screen look nicer in the field?"

So did it, moved the ISO back to 800, screen got dark but it's not like everything disappeared. Manual focused, took the single exposure, and went home. Then played around with the exposure and highlight sliders in Lightroom for, don't know, about 15 seconds or so. What a thrill to get a better result with exactly the highlight preservation or blowout desired, decided after the fact in the optimal editing environment of the "darkroom." No exposure bracketing in the field, welcome simplification when there are about a zillion other things to think about and adjust. I.e. bracketing completely pointless since there is absolutely no chance of blowing highlights on a greatly underexposed image, and the "final exposure" is set at editing time. Really in a sense the rawest of all possible raw files.

Now leaving your camera at some lower ISO when you "need" a higher ISO only makes sense if (a) the ISO you leave the camera at indeed has better or no worse read noise and (b) you have verified that everything looks exactly the same or better whether you let the camera firmware "amplify" the brightnesses for you in the raw file, or you let your post-processing software do the "amplifying" arithmetically. Both of which have verified are true in the Nex 3/Lightroom case--even if you need ISO 12800, you can get "the same" or better results by post-processing an image from a camera set to ISO 800. Thus the Nex C3 is a good deal of the way towards being Iliah Borg's "true ISO-less camera."

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

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