Cruising with the Sony a7RII – Exposure strategy

This is a continuation of a report on a trip with the Sony a7RII. The series starts here.

I ended up using ISO 100 and ISO 800 for virtually all my exposures on the Alaska trip. Since the a7RII is fairly ISOless from ISO 100 through ISO 500, there is little reason to use ISO settings 125 through 500; you’ll get pretty much the same shadow noise shooting at ISO 100 and pushing in post, and, if you do that, you’ll have a lower probability of clipping highlights. At ISO 640, the a7RII changes its conversion gain, and exhibits lower noise, so there are advantages in using that ISO setting over ISO 100 and a 2 2/3 stop push in post. After that, the a7RII returns to ISOless behavior, so there is negligible shadow improvement to be had from cranking up the ISO setting, and the same highlight advantages pertain. After a certain point, as the light drops, the finder image will become unusable and you might well exceed Lightroom’s pushing capability, but I never encountered light that dim on the trip, since I slept through the Aurora Borealis display the only night we had one.

“Why ISO 800?” I hear you asking. “Why not ISO 640, since that’s all that’s needed?” The answer lies in the way the a7RII’s controls operate. With the camera’s controls set to their defaults, pressing the right side of the back wheel allows you to change ISO, and rotating the back thumbwheel lets you change the setting in whole -stop increments, rather than the third-stop increments of the back wheel. So, to get from ISO 100 to ISO 800 is a matter of one press of the back wheel and three clicks of the thumbwheel. Same for getting from ISO 800 to 100 100. ISO 800 is close enough to ISO 640 for my purposes.

For most situations, I like using aperture exposure mode, and multi-metering. I don’t use the meter as the final arbiter of exposure, but using it with active use of the exposure compensation control allows convenient adaptation to rapid changes in lighting. Also, since the exposure control is just about the only direct adjustment on the camera, using it lets you see its setting at a glance.

How do I decide on the exposure? If the bright parts of the subject are fairly neutral in color, I use the live (luminance) histogram, supplemented by occasional taps at the playback button and observation of the three-channel histogram and looking for blinkies. I have been experimenting with turning zebras on at a setting of 95%, but I haven’t developed confidence in that method yet. I tweak the exposure compensation dial to get the histogram I want.

On the trip. this technique served me well with a few exceptions.

The first is the obvious one; the darkest setting on the Sony a7x exposure compensation dial is -3 stops, and that’s just not enough for shooting into the sun with small areas of the picture composed of clouds and water, and large amounts of dark trees. When that happens, there are two things I do. If it’s only going to be a couple of shots for which I have to deal with the problem, I’ll change the field of view to include more bright elements, press down the exposure lock button, and recompose. If I’m going to be making more than a handful of exposures, I’ll switch to manual exposure mode.

I wish that the range of the exposure compensation control were from +2 to -4, rather than plus and minus three stops. I have never found a situation where I needed +2, let alone +3.

Another situation that causes trouble – it caught me once on the trip – is one or two isolated very bright areas. The live histogram window on the a7x cameras doesn’t go all the way to the right-hand side of the EVF; there is a little bit of the preview image to the right of the histogram. If that part of the preview image is fairly light, you can’t clearly see the right-hand bucket of the histogram. Normally things kind of tail off at the top of the histogram, but sometimes there’s a spike on the right with unpopulated buckets to the left of it. Most of the time, that’s OK, too, since the right hand bucket is measuring specular highlights, which are usually best clipped.

Here’s how I got caught out. I was shooting a calving glacier from a Zodiac, kneeling on the floor with my elbows on the tube, looking into the sun with the WATE, trying to get the sun and its reflection In the icy sea. If the sky had been clear I wouldn’t have had a problem, but it was hazy, causing the sun’s light to spread out. In my awkward position, I didn’t take the time to check the three-color histogram or look for blinkies. That was an error. The resultant images had blown areas extending irregularly out from the sun, damaging the image. Had I known, I would have switched to manual mode and made the exposure very short, making the blown areas smaller.

Here is the result of double development in Lr, followed by a  lot of masked blending and masked curves:

It still looks fake. It will take some more work, possibly with the aid of an HDR program.

In case it wasn’t clear at the beginning, let’s go over how I managed the ISO “knob” on this trip. The default setting was ISO 100. If there wasn’t enough light for ETTR at ISO 100, I set the aperture to what I wanted and cranked the exposure compensation dial in the negative direction to obtain an acceptable shutter speed. As the light fell, when the dial got to -3, if the highlights had plenty of room, I changed the ISO to 800 and did the same thing at that ISO. Pretty simple, huh?

Some have objected to the variable “underexposure” technique that I recommend for ISOless cameras from the perspective that it requires individual adjustments of the Exposure slider in Lightroom for each picture. I usually say something like, “So?” However, for those for whom adjusting exposure in post for each and every image is a terrible privation, here’s a suggestion to Adobe for a future option in Lightroom: look at the exposure compensation setting in the EXIF data, and compensate the Exposure accordingly.