ISOless sensors, read noise and photography - many questions!

Started 10 months ago | Discussions thread
boardsy
Senior MemberPosts: 2,197Gear list
Like?
but is your ISO3200 as good as ISO800? :-)
In reply to RussellInCincinnati, 10 months ago

RussellInCincinnati wrote:

Alan, am so glad you raised this thread.

Thanks - though I was merely piggy-backing on the back of a few feverish "Is ISO part of exposure?" (- "no!") thread-wars!

As a raw file user, am never going to set the Nex C3 above ISO 800 again. Because as you found also, can verify that just brightening the "underexposed" (say "ISO 3200") image in, for example, Lightroom 4.4, completely eliminates the need for bracketing exposures in the field. Amazing and embarassing to not have noticed this years ago.

It's not obvious (or embarrassing not to have known) that many (most?) high ISO values in many (most?) cameras are not a useful sensor sensitivity gain, but simply a tag in a RAW file to tell the JPG or RAW software where to set brightness, and stretching the actual exposure (aperture & shutter speed) over the available brightness levels, so "high ISO noise" is in fact low exposure noise, exposed (!) by raising brightness levels!! I've only just discovered all this, in a personal Copernican ISO revolution!

Thanks also to DPreview for the Photo Science and Technology forum, and the sensorgen website. A great practical benefit after only a couple of days of perusing the forum, and noticing that setting a Nex C3 above ISO 800 cuts dynamic range as much as it raises brightness (i.e. is potentially pointless).

If had a Nex 7, would probably never set the ISO above 100. Because you don't "get anything for it" in terms of lower-light noise advantage.

It's true that the playback of "underexposed" images is not so nice in-camera, but decades of film photography, and awareness that have never sold a digital photo that didn't need some post-processing, makes me not miss that delicacy. And as you pointed out, heck you can take a moment to set your ISO high and take a test shot, if you're so anxious to see a somewhat-closer-to-final version of your photo, in-camera.

Details

When "pushing" underexposed Nex C3 raw files taken with camera set to ISO 800, can see no significant (i.e. noticeable) difference in anything one might think of to call "image quality". If there are banding or shadow etc color tint challenges to "pushing" the exposure in Lightroom 4.4, well Lightroom apparently knows how to deal with them. Put another way, in the Nex C3 case, Lightroom seems to know enough to do as good a job as Sony in amplifying the ISO 800 raw-data brightness of dark images (at least to ISO 3200 which I never go over).

ISO 3200 photo:

ISO 800 photo, "exposure" slider simply set to +1.75 EV (exposure values, F-stops) in Lightroom:

With results this similar, why would a raw user ever take bracketing exposures because of a worry about highlight detail, or bother setting a Nex C3 beyond ISO 800?

Exposure bracketing when you're above ISO 800 is clearly an antiquated artifact of the film era, if you're using raw files on a Nex C3. Instead of clogging up your camera with "bracketing in the field" images, you just have the luxury to play with the "exposure" slider (in say, Lightroom 4.4) until you get the overall brightness you want from some "underexposed" raw file. What an embarassment, looking at all the unneeded bracketing exposures in my image database.

Obviously all this is a time/error-saver for raw users of a Nex C3 taking real photos in the field. Where they otherwise would have fiddled with their cam to get it over ISO 800, or waited while their camera clattered through bracketed exposures, or been held up from taking their next exposure, while waiting for all the unnecessary raw files to shuffle on out to the memory card.

And what a delight to know that, without bothering with bracketing, you have always preserved highlight detail, in case you want the HDR look from a single exposure:

Hmm, you've gone and done it now - the ISO3200 shot seems just as good as the 800 version! Did it require careful RAW noise reduction or other massaging? My whole line of questioning was that ultimate IQ should bebetter by "doing high ISO" (raising brightness, pushing shadows etc) in RAW! Ok, it may be easier to set and forget ISO800 in the field, but is the struggle with a dark screen image really worth it? Of course, if preserving important highlights, if a high ISO will blow them, but otherwise? I'm not so convinced any more!!

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Regards,
Alan
my Flickr

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