Saturday, August 25, 2007

The Sunny F16 Rule

I have a great light meter. And the meters inside a modern digital SLR are usually spot on, if used correctly. Still, in the same way it's valuable for a musician to have perfect pitch, it's probably good for a photographer to have some sense of light. So, how can you develop that?

Well, it's a bright, sunny day, I've got my trusty Zorki 6 and a Metro card. There's no meter in the Zorki rangefinder -- so I can carry a meter or I can make my best guess as to the right exposure....

Today I'll guess. That's a great way to train your eyes -- but you'll need a good Rule of Thumb to work from: The Sunny F16 Rule. On a typical day, your exposure can be calculated in the following manner:

Shutter Speed:
What film speed or ISO setting are you using? To start the calculation, set that as your shutter speed.

shadows sharp: F16.
soft-edged shadows: F11
barely-there shadows: F8
very overcast: F5.6
Since I have 400 speed film in my Zorki, I'll start with my shutter speed at 1/400th of a second. Then, I'll look at the shadows I see and decide: sharp, soft, or very soft? F16, F11, or F8. If the clouds roll in and I notice it's darker, then F5.6.

So, I might start at 1/400th of a second and F16, but if I see the light level lower a bit switch to F11. If I see the shadows have faded, then F8. Easy, and great training for your eyes.*

*(Of course, while I want to make things simple for this post, in the real world there is a tiny bit more complication: I like to slightly overexpose black and white negative film. Like many, I find a 1/2 stop of overexposure makes a better negative, generally, even though I would avoid overexposure in digital whenever possible. So, to do that I would make a little adjustment to my calculation: my 1/400th shutter speed would change to about 1/250th. That's very convenient, since the Zorki doesn't have a 1/400th setting anyway, so I'll switch to 1/250th at F16 for the bright sun.

Then, since I find 1/250th isn't quite fast enough for walking along street shooting -- Garry Winogrand used 1/1000th when possible on the street -- I would switch to the Zorki's fastest shutter speed of 1/500th and make the corresponding change to my aperture.

So, I would shoot at 1/500th and F11 in sharp shadows, 1/500th and F8 when the light drops a little and I see soft shadows, and 1/500th and F5.6 when the light drops further. If the clouds roll, then I'd be at 1/500th and F4.)

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