If you’ve read the last four or five posts, it’s probably occurred to you that, in the new high resolution digital image, focusing is a challenge. Indeed; if you want to take full advantage of all the pixels that modern technology can give you, I think focusing is the most problematical operation in photography.
It wasn’t always so. When we had manual focusing, we had better focusing aids. In the 35mm and medium format SLR world, we had microprism collars and split image centers on the focusing screen. With view cameras, we could plunk a 10X loupe over the ground glass.
With medium and small format cameras, the resolution of the film we used wasn’t that great. That gave us two advantages in focusing: we could use smaller (numerically larger) f/ stops without worrying about diffraction, and if we were off a little bit, the film had a hard time resolving it.
Autofocus came along, and we gained in focusing speed, but sometimes lost in consistency and accuracy. The optical focusing aids in the finder disappeared as the manufacturers figured that people didn’t need them anymore. The autofocus lenses didn’t have the nice feel of the old ones when manually focusing, and the amount of rotation for a given focus shift got smaller.
At first, the digital cameras worked about like the film cameras that they largely supplanted. But the sensors grew larger and denser. This was great for quality, but now many of the sensors are unmerciful in revealing focusing errors, and even higher resolution sensors are on the horizon.
What to do?
First, make sure your autofocus is doing the job. Check every body/lens combination; it’s quick and easy, and you can often dial in corrections that the camera will remember. If there are body/lens combinations for which autofocus is not reliable, use an eyepiece magnifier or live view in situations where you know that depth of field is not going to paper over misfocusing.
More to come on each of these.