By MICHAEL PERKINS
IF YOU ARE EVEN HALF AS LAZY AS I AM, you welcome practical shortcuts to the kind of calculations and measurements that used to consume about half our time as shooters. Looking back at the light exposure graphs, aperture conversions, and flash charts of the camera tutorials of just a generation ago is enough to remind you of every time you ever hooked math class or paid someone else to take your quiz on the periodic table. Some of us photomaniacs were born with the combined skills of Ansel Adams, Pythagoras and Ptolemy, and the rest of us just take pictures as best we can.
I believe in getting on with things, and I’m not proud about consulting books with the word dummies in the title. So, I most strongly suggest, that, if you do not yet have a smartphone app that acts as an instantaneous depth-of-field calculator, that you download one as fast as your little text-weary digits will allow. They are generally free, and are offered by literally dozens of vendors. They are fast. They work. And they help minimize the amount of blasphemy uttered by your humble author. Mostly.
The apps are very simple. You dial in the lens you’re using, the f-stop you want, and an approximation of the camera-to-subject distance, and hit “calculate”. The app tells you in feet (or metres) where the near and far focus point for your subject occurs, and how many total feet of sharpness that equates to. This kind of thing is extremely handy to jog your thinking out of traditional mode, as in the picture below.
In the above image, I wanted to shoot the interior lights of the back of my house and their reflection on our pool. The two normal ways to do this:
1) get on a tripod, dial up an aperture of about 6.3, use a remote release and click off a 10-15 second exposure depending on how much deep detail you need. That takes setup time and precludes your shooting on a whim or in the moment, but it allows you to go noise-free, since for a time exposure, you can stay at ISO 100. I also could opt for:
2) An instant shot with the ISO cranked to 600-1000, again at a medium focal distance, but with the chance that noise is going to be more noticeable.
The DOF app let me quickly figure out a third way. Since I was using a 35mm prime lens, I was going to open up all the way to f/1.8 and suck light like a demon, facilitating a quick exposure and the ability to stay at low ISO. Shooting that particular lens wide open guarantees a shallower depth of field than in the other two methods, but, while DOF for a macro image, shot about a foot away at 1.8, is very shallow, shooting at far objects with the same aperture can give you plenty of room to work in. Dialing my coordinates into the app, I could see that sharpness would kick in at about 20 feet (just beyond where the pool decking bricks meet the edge of the pool) and stay solid till well past 32 feet. The twelve feet of usable sharpness would be more than enough to capture what I wanted, since anything ahead of (or behind) my “sweet spot” would be shrouded in darkness.
If I wanted to show additional detail in the surrounding yard, play up the texture of the pool decking, or give an overall glow to the shot, I could still shoot it on a tripod and just lengthen out the exposure, but for this specific set of data, the 35mm prime, wide open, would give me the look I wanted. The DOF app was just a way to get a quick calculation without fumbling with my slide rule in the dark, and to check my thinking in the moment.
For a near zero investment, you can’t find a better friend out in the field. And if you’re a really avid photographer, you can use all the friends you can get.
Especially one who’s more gooder at math than you are.