A reality based independent journal of observation & analysis, serving the Flathead Valley & Montana since 2006. © James Conner.
Autofocus does not work well for low contrast, smoke veiled subjects. I’m compiling a timestamped visual history of the visibility from my front porch by photographing Kalispell Regional Hospital, which is a bit less than two miles distant. When the hospital fades into the haze, which it started to do around 1100 MDT today, the particulate concentration is high. When I made the image below, the concentration was 141 µg/m^3. Two hours later, the concentration had doubled to 282 µg/m^3.
Ordinarily I use an 18–135mm or 55–200mm autofocus zoom with my DX DSLR (and a tripod), but with the heavy smoke we’re experiencing, each lens hunts for, but misses, sharp focus much of the time no matter whether I use phase or contrast detection autofocus. The solution, of course, is manual focus. Neither zoom, however, is easily focused manually. Therefore, I’ve been using a 30-year-old manual focus lens, a Nikkor 135mm f/3.5 Ais telephoto, that has a hard stop at infinity. At f/8, it’s just as sharp as my autofocus lenses, and much easier to use in this situation.
If you don’t have the option of using an old manual focus lens, and you’re having trouble focusing on a soft, low contrast target at a distance, see if your camera has a landscape mode that sets the lens to infinity. Otherwise, bracket your focus.