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Matador staff writer Jeff Bartlett illuminates some simple but essential photographic math.

It’s all too easy to say I’m not interested in the technical aspects of my craft. I like to take photographs more than I like to do math.

Yet, I still know that 1/250 f8 equals both 1/2000 f2.8 and 1/30 f22. All three are identical exposures. I also use the following 5 formulas every time I pick up my camera.

1. Camera shake

This is the most important formula to use and understand. While I often believe I can handhold my 200mm lens for a quarter-second exposure, the resultant soft images are proof I am wrong. If I notice my images aren’t tack sharp, I double check my shutter speed and adjust it within the confines of this simple formula:

1/focal length = minimum shutter speed

If I can’t increase my shutter speed, I reach for my tripod.

2. Sunny 16

My parents used to hand me a yellow and black Kodak disposable camera whenever we went on holiday. Every image turned out the same — everything was in focus and each exposure was spot on. Those cameras were the Sunny 16 blueprint:

Sunny weather + f/16 + 1/ISO shutter speed = proper exposure

These same camera settings also apply to capturing the surface detail of a full moon, but don’t expect any light to appear in the foreground.

3. f/8 and be there

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Legendary photojournalist Arthur Fellig coined the phrase “f/8 and be there” in the 1920s. It’s a sound formula because to make a successful image, you need:

Although this phrase has been around for 90 years, it’s still sound advice that I use when I’m shooting multiple assignments or subjects in a short time. With the camera set on aperture priority mode at f/8, my shutter adjusts automatically to the ambient light and the aperture allows a photographer-friendly margin of error when focusing.

4. Inverse-square law for light

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The definition of this law — that the quality or strength of light is inversely proportional to the square of the distance of the subject from the light source — sounds scary enough that I’m often tempted to sell my off-camera flash setup. But it’s quite easy to put into practice:

1/distance between light and subject2 = light on subject

I find it easiest to think of it in layman’s terms. Whenever the distance between the subject and flash is doubled, the subject receives one quarter of the light.

5. 600 star rule

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Star photography is booming, if’s bestselling photographs page is any indication. More than 20% of the top sellers highlight the night sky.

The first decision I make when shooting stars is whether I want them frozen in place or streaking across my frame. Quite often, I choose the former because I simply love the look of the Milky Way in a silhouetted landscape. To determine the longest possible shutter speed before the stars will appear in motion, I use this simple formula:

600/focal length = maximum shutter speed

About The Author

Jeff Bartlett

Jeff is an adventure photographer and writer with a penchant for masochistic outdoor pursuits. He is now based in Jasper National Park. More of his work can be seen on his website and blog. You can also find him, periodically, on Twitter.

  • Sparkpunk

    This is great…thanks for this! The Sunny 16 rule saved my ass when learning how to shoot sans-light meter, but I had no idea about these other ones…looks like I’ve got some homework to do….

  • Nathan Myers

    Great stuff.

  • Nick Miners

    The camera shake rule was thought up in the days of 35mm film. With modern cropped sensor DSLRs, you need to use slightly faster shutter speeds than you used to, e.g. with a 35mm lens you should stick to 1/50 or slower as the field of view is equivalent to a 50mm on full frame camera. I wasn’t aware of the 600 star rule however, so thanks for that!

  • Melinda Brasher

    Thanks. I used these for my algebra students–real life uses of formulas.

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