Zebra and highlight clipping

Discussion in 'Sony Alpha E-Mount Cameras' started by pdk42, Jun 20, 2017.

  1. pdk42

    pdk42 TalkEmount Regular

    127
    Nov 26, 2014
    I picked up my new-to-me A7Rii on Saturday and in playing around doing some comparisons to my E-M1ii I noticed that the zebras on the Sony (set at 100+) start showing a long time before the highlight indicators do on the Olympus. I didn't really believe that the Sony sensor was clipping before the Oly (!), and indeed it does seem the case that the zebras are very conservative since highlights were easily recoverable even in areas heavily populated with said stripey animals.

    I did some simple testing today to get a feel for how conservative it is and the answer is a little under 2 stops. That is, if you increase the exposure comp from the point where they just show, you can add another 2 stops and still be able to recover the highlights in LR (I'm talking raw of course). In fact, the histogram on both the camera and in LR confirms this to be the case (i.e. it's 2-stops after zebras appear that the histogram starts slamming up to the right hand side - and I was pointing at white light so the RGB values were all pretty even).

    It's odd that the zebras behave like this. I noticed another odd thing too. If I set the zebras to values lower than 100 and then crank the exp comp up a bit at a time, then zebras appear only to disappear again when the exp comp goes on about another 4 stops. Not a situation that will affect me, but very odd nonetheless.

    I'm a bit disappointed by this since my standard exposure method since taking up mirrorless is to use the exp comp dial a lot, guided by highlight clipping indicators. The Oly isn't perfect (esp in M mode), but it does seem a bit easier to use than the Sony. I guess I can adapt, but it's a bit of a pain having to go back in exp comp until the zebras disappear and then carefully add back a stop and a half or so.
     
    Last edited: Jun 20, 2017
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  2. Kiwi Paul

    Kiwi Paul TalkEmount Top Veteran Subscribing Member

    767
    Feb 14, 2016
    Aberdeen, Scotland
    Paul
    Can't comment Paul I don't use the Zebra, I use the Histogram if I want to see the exposure.

    Thought you were in America?
     
  3. fractal

    fractal TalkEmount Hall of Famer Subscribing Member

    Jun 17, 2014
    Southeastern PA
    Chris
    Zebra vs. histogram - apples and oranges.

    Zebra tends to be more sensitive to highlights. A lot depends on your settings. I don't use Zebra but my general understanding is that is more a tool for video vs. stills.
     
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  4. pdk42

    pdk42 TalkEmount Regular

    127
    Nov 26, 2014
    Yes, I am. Chicago. Work all week, but hopefully some downtime at the weekend.
     
  5. pdk42

    pdk42 TalkEmount Regular

    127
    Nov 26, 2014
    I did a bit of digging and indeed you're right.

    The zebra value is something defined by the Institure of Radio Engineers (IRE) and a value of 100 indicates a brightness level on the video signal that will give pure white on NTSC/PAL - so it is not an indication that it's clipping. Whilst it could be used for determining blown areas with some interpretation, that's not its designed function (as I found out!). Settings less than 100 have a "range" I suppose because they are used for things like exposing correctly for skin tone. Goldilocks exposure - not too much, not too little!

    It opens up a wider discussion of course on how to set the right exposure in challenging scenes. One of the big advantages of the A7Rii to me is the DR. That's only of real value if I expose to make best use of it. I know there are lots of metering modes to play with (and I even have an old lightmeter) but actually a well-implemented clipping indicator beats all of that since I can expose for the highlights and worry about the shadows later. I've personally never found in-camera histograms to be much use for this. That there is some data at the far right (or beyond) is often hard to see; and of course it tells you nothing about what is blown.

    The Olympus system works very well IMHO. The highlight clipping indicator is perhaps 1 stop below real clipping which means I can set the exposure quickly such that only the very slightest indicators are showing and I then know that I'm pretty close to maxing out the sensor.

    What do the rest of you landscape types do?
     
    Last edited: Jun 20, 2017
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  6. Tipton

    Tipton TalkEmount Regular

    187
    Jan 30, 2016
    Rae Leggett
    All I do is watch my histogram and adjust accordingly. Zebra annoys the heck out of me, so i don't use it. I've also learned to accept a little bit of clipping on either end. If it's bad, I'll do HDR, but I'm trying to get away from that, and optimize in the camera.
     
  7. firemist

    firemist TalkEmount Regular

    159
    Dec 4, 2015
    Well, Fred Miranda tested on the A7r (I believe) and confirmed the 2 stop leeway for ETTR. I use that most of the time; set 100+ for Zebras, adjust the EC dial to just eliminate the stripes in an important HL area, then I generally add back around 1.3 EV. Why throw away some expensive pixels, lol. In Lightroom, I generally reduce the Exposure a bit to get a nice mid-tone then set the whites and blacks.

    I shoot almost always in A mode.

    I hear some people set the Zebras to 70 to get proper skin tones. Maybe they are the folks shooting video.
     
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  8. pdk42

    pdk42 TalkEmount Regular

    127
    Nov 26, 2014
    Yes, that sounds like a good strategy. I think it's what I'll use (but maybe go to 1.5 EV).
     
  9. chonbhoy

    chonbhoy TalkEmount Regular

    79
    Jun 19, 2017
    Would using ISO 50 work in the same way and only use +0.5 or +1.0 EV?
     
  10. firemist

    firemist TalkEmount Regular

    159
    Dec 4, 2015
    It should work regardless of ISO, still with up to +2EV. You might want to shoot some test shots and see how your camera responds to +0.5, +1.0, +1.5 and +2.0 EV
     
  11. chonbhoy

    chonbhoy TalkEmount Regular

    79
    Jun 19, 2017
    I thought you lose highlight data when using ISO 50, ill give it a go.
     
  12. addieleman

    addieleman Passionate amateur Subscribing Member

    Nov 13, 2012
    Netherlands
    Ad Dieleman
    You will, if you expose like the light meter says. E.g. in sunlight the camera will indicate something like f/8 - 1/400 s at ISO 100 and f/8 - 1/200 s at ISO 50. In that case you'll lose headroom in the highlights of 1 stop at ISO 50 compared to ISO 100. ISO 50 is kind of fake, it's just the same as ISO 100 with a +1 EV exposure compensation.
     
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  13. chonbhoy

    chonbhoy TalkEmount Regular

    79
    Jun 19, 2017
    In an effort to rinse as much out of the sensor as possible would ETTR benefit using ISO50 which has less noise or is it just a trick and it really doesnt have less noise?
     
  14. addieleman

    addieleman Passionate amateur Subscribing Member

    Nov 13, 2012
    Netherlands
    Ad Dieleman
    According to Bill Claff's measurements the photographic dynamic range for ISO 50 is the same as for ISO 100 so using ISO 50 doesn't bring you anything in this department. Or in any other department for that matter.
     
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  15. chonbhoy

    chonbhoy TalkEmount Regular

    79
    Jun 19, 2017
    Thats good to know.
    Is it equally true to say that ISO50 is equally as good as ISO100 in the dynamic range then?
    The other department would be noise and a lower ISO would be better wouldn't it? Usually that's at the expense of dynamic range when its below base but Bill Claff's measurements suggest otherwise.
     
  16. fractal

    fractal TalkEmount Hall of Famer Subscribing Member

    Jun 17, 2014
    Southeastern PA
    Chris
    The only time I use ISO 50 is in long exposure shots.
     
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  17. Kiwi Paul

    Kiwi Paul TalkEmount Top Veteran Subscribing Member

    767
    Feb 14, 2016
    Aberdeen, Scotland
    Paul
    I think ISO 50 is purely to allow a longer exposure, it has no benefits W.R.T noise or DR etc, the sensors base ISO will surely always give the best performance.
     
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  18. addieleman

    addieleman Passionate amateur Subscribing Member

    Nov 13, 2012
    Netherlands
    Ad Dieleman
    The "extended" ISO values below ISO 100 do not offer any benefits in terms of noise, dynamic range, whatever. I personally can't think of a a reason why you'd want to use ISO 50.
     
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  19. WoodWorks

    WoodWorks Super Moderator Subscribing Member

    Dec 12, 2012
    Ashland, OR, USA
    David
    Wait... someone here posted noise samples from some test that showed small, but noticeable noise improvement at ISO 50. Let me do some digging.
     
  20. WoodWorks

    WoodWorks Super Moderator Subscribing Member

    Dec 12, 2012
    Ashland, OR, USA
    David
    Here it is, from the infamous Tony Northrup:



    He claims that you not only get a slight reduction in noise by shooting ISO 50 vs. 100, but if you expose correctly for the (now reduced) highlight range, you gain a slight increase in your ability to recover shadow information.

    I have yet to test this myself, but I can't see any problem with his conclusions. Did I miss something?
     
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