There’s a maxim in medicine: “If you hear hoofbeats, think horses, not zebras.” It means look for the most common maladies first. I’ve always liked that rephrasing of Occam’s Razor.
What’s that got to do with today’s topic, which is using the zebra viewfinder display option in the Sony alpha 7R Mark II (a7RII to its friends)? Nothing, really. I guess I was just free associating.
The a7RII zebra option shows areas in the live image in the finder that have greater than a certain exposure as black and white diagonally striped areas. The least sensitive is labeled “100+” in the menu (Gear->1->first entry).
I set the setting effect to “on”, the zebra sensitivity to “100+” and pointed the camera at a white target that was lit with a 5500 degree Kelvin light. I adjusted the exposure so that I could just see the zebras. I looked at the histogram. The top part of the populated area was just under 10% of the way from the left to the right side. That’s a bit under a stop.
Thus, setting the zebras to 100+ and adjusting the exposure so you can’t see them will give you an exposure that’s even less optimum (in ETTR terms) than looking at the histogram. It’s a conservative way to avoid clipping, though.
I don’t know for sure, but I assume that the zebras are derived from the preview image in much the same way that the live luminance histogram is, and that they may give you the wrong answer for highly chromatic subjects or infrared-modified cameras. If that’s true the zebras could be made less conservative (in the sense that they tend to err on the side of avoiding clipping) by the techniques used to make the live histogram more closely represent the real raw histogram, but they’ll always be more conservative than the live histogram.
What if you use one of the really flat log profiles meant for cinema?
I think exposure comp doesn’t affect the zebras. — if so setting it to +1.3 stops and then exposing for backing off the zebras might give quite a good tesult…
As Lynn said, in the a7X cameras, exposure compensation does indeed affect the zebras.
Lynn Allan says
I’m finding that using:
* zebras 100+
* with UniWB (according to JK article w/Excel spread sheet)
* and PictureStyle Neutral
** with Contrast -3
** and Saturation -3
results in exposure pretty close to ETTR.
David: My observation is that EC (exposure comp) changes the zebras, at least in “A” (aperture) mode.
Thanks, Lynn. That’s useful.
Thanks Lynn, Jim. Good to know.
on an unrelated subject – did you find that AF focusing in the dark conditions with a nominal ISO locked @ ISO100 works worse than ISO for example being way higher ?
Good question. See this post:
See this: http://blog.kasson.com/?p=11885
John Clark says
I use the zebras at 100% on the A7RII, but just to remind me if there is an issue, but all the time @100+ on my a5000 IR camera to get the right amount of exposure, which is indicated at 1.7 to 2 stops over exposed That, along with Focus Peaking (in Yellow so you can see them against the red) is the only way to get sharp IP photos.
Lynn Allan says
> The top part of the populated area was just under 10% of the way from the left to the right side. That’s a bit under a stop.
My experience is that the histogram on the a7Rii is too small to feel confident about really using the right side. Is there a setting I’ve overlooked to get the histogram to expand to the full LCD?
Also, the base-line showing the horizontal axis seems too thick to see just what is going on.
I’m been reluctant to gradually increase the exposure until I see a spike on the right side, then back off a bit. I guess that is appropriate.
Also, there can typically be spectral highlights that I will allow to blow out … histograms are less useful for that, and the zebra’s are very valuable.
A pet peeve: it doesn’t seem to be possible to turn off the “under-exposure warnings” and leave the “blinkies” operational. I suppose if you had a very flat, low contrast scene, it would suffice to dial up exposure until the “under-exposure warnings” went away, but that could be quite short of ETTR.
If you cycle through the DISP settings, you’ll find one that makes the histogram quite large, but you can’t see our subject in that mode.
I do that sometimes. It works fine.