Monday, February 18, 2013

Zone Focus Test With the Fujinon 14mm Lens

Wow, was it ever cold in New York on Sunday! The wind chill was brutal, but I was itching to try some focus tests and I was blown away by the results. But first some clarification. Hyperfocal distance is the closest distance that a lens will be in focus and still be able to keep focus at infinity reasonably sharp. Zone focusing requires that the lens have distance indications on its barrel for each appropriate aperture setting, thus allowing the photographer to set the range of distances within which any objects will appear reasonably in focus. When I shot film in my Leica M6 I often used zone focusing, but rarely  the hyperfocal distance. With a very wide angle lens, such as the 14mm, I'm shooting to create a perception of great depth, I don't really care that objects in the far distance are out of focus. But when I shoot street, and especially when shooting from the hip, sometimes the autofocus on the camera either doesn't understand what I want to be in focus (it's often an object or person at one side of the frame, while the focus point for the sensor is set for the center of the frame) or the autofocus lag (even at 1/10th second) misses the shot. The first case scenario happens more than I'd like, the second case much less often - so much less that it's not even worth considering.

When I decided to run this test I wanted to err on the side of caution, so I opted to shoot part of the afternoon in autofocus, just to make sure I'd get some good shots to show for my afternoon of braving the cold. The zone focus shots were taken at f8 (less than that would have narrowed the depth of field unacceptable for the test) and 1/250th second, which put my exposures in the high ISO range - not a problem for the X-Pro1 processor. Here's a calculator to play with to discover acceptable in-focus distances. Remember that this calculation has nothing to do with the quality of the lens, the parameters that affect the calculation are the lens focal length, the aperture setting, and the distances involved. All the rest is pure physics and math. If I set my 14mm lens at f8 and the focus at a distance of 4 feet, my nearest acceptable in-focus distance will be a tiny bit over 2 feet away and the farthest will be 243.5 feet. If I set the focus point for 1/2 foot closer, 3.5 feet, that range drops from 1.9 feet to 24.9 feet. So to achieve a difference of about 1/10 foot closer, I'd have to loose about 220 feet in distance. Given the way I shoot, in close, I'd go for the closest possible I can get and still bet some reasonable distance focus. Even at a focus point of 3 feet I can get an acceptable image from 1.75 feet to almost 10 feet. That last zone is probably the best for me. That's why I love using very wide angle lenses. I would suggest to anyone that they play with this calculator to get a feel for how the calculations work, so that out in the field there is a lot less guessing. If you happen to be a math wizard, you might want to make note of these formulae and when your out in the field do your own calculations (while I take the pictures). 

These first two shots were taken with the autofocus, through glass, and the camera nailed the focus.

Open .... Slurp

Mommy Feed Me

The next two shots were made with an f8 zone focus setting.



So Sad

This last shot was autofocus at an ISO of 6400 - amazing!

Run For The Exit!