This one caught me by surprise. I was walking around looking for photo ops in full daylight. I checked my Canon 7D settings and it was set for ISO 200. I thought that was really odd, so I decided to manually change it. The camera jumped from “A” directly to “200”, not “100”??!! I was almost certain that the camera had an ISO 100 setting, but I had been switching cameras on different assignments, so maybe I was confused. When I had a chance, I checked the specs for the Canon 7D on the Canon USA site. It lists ISO 100-6400. What the frak?? (Yes, I just watched Battlestar…)
Well, do you see the D+ setting above the 200? That’s the reason. The D+ means that Highlight Tone Priority has been enabled. According to the Canon 7D manual, Highlight Tone Priority
improves the highlight detail. The dynamic range is expanded bewteen the standard 18% gray and the bright highlights. The gradation between the grays and highlights becomes smoother.
Translation — additional data is collected for the highlights which prevents complete white blow-outs. However, this feature does have a sacrifice — you loose ISO 100. Even if the highlight appears white, by shooting RAW, there will be additional data when you adjust the exposure or use HDR.
The setting for Highlight Tone Priority is hidden in Custom Function II, Option 3. See below:
Once enabled, you will the the D+ appear in the ISO setting.
If you shoot in bright light or your subject has plenty of highlights, this setting can be very beneficial during post-processing.