One of the challenges of using a 35mm film camera is many of the older models do not have electronic light meters, and the ones that do have Light-meters require batteries. When the battery for my Fujifilm X-T2 digital camera is exhausted, I can quickly pop in a new one. Changing the battery in some film camera, e.g. the Pentax ES II, is a bit more challenging.

To get around the need for a light meter, some photographers use a rule called “sunny 16” or “sunny f/16 rule”. This “rule” recommends that, on a clear and sunny day with distinct shadows, the photographer set the camera exposure (aka shutter speed) to the inverse of the film ISO when the lens aperture is set to f/16. For example, if shooting a roll of Ilford HP5 Plus 400, a good starting point for shutter speed would be 1/400 sec; for Kodak Ektar 100 it would be 1/100 sec.

But what if you want to shoot at f/8 instead of f/16? Reduce the exposure time by a quarter or $\tfrac{1}{x^2} \$ where x is the change in the aperture, which in this case was two full f-stops. On a clear and sunny day, a roll of Ilford HP5 Plus 400 at f/8 could be exposed at ½2 x 1/400 = ¼ x 1/400 = 1/1600 sec. But what if the sky is cloudy or I am shooting indoors? It gets complicated. Some photographers are good at mental math or maybe memorised a table of possible values or with experience, have just learned what to do for most situations.

I have no intention of doing the mental math required. Despite a college minor in mathematics (differential equations, algebra and other abstract math are required for engineering students), I’m not good at mental arithmetic. It’s my Kryptonite. Fortunately, I don’t have to do any math. There is an app for that; the Sunny16 exposure calculator. I installed this app on my iPhone. Whenever I need to use the Sunny f/16 rule, I will consult this app to find the combination of aperture and exposure for the given screen.

I copied the following table from Wikipedia and added a column for exposure at ISO 100.

Aperture Lighting Conditions Shadow Detail Shutter speed at ISO 100
f/22 Snow/sand Dark and sharp edges 1/50 sec
f/16 Sunny Distinct 1/100 sec
f/11 Slight overcast Soft around edges 1/200 sec
f/8 Overcast Barely visible 1/400 sec
f/5.6 Heavy overcast No shadows 1/800
f/4 Open shade/sunset No shadows 1/1600

When I first learned about the Sunny 16 technique I was sceptical and critical. In fact, I was downright antagonistic in my comments on the blog post. But a recent experience with a roll of improperly exposed Kodak Ektachrome 100 and a short email exchange with Hamish Gill made me reconsider. Had I learned more about the Sunny 16 rule I would have realised that the rule starts with the assumption that your lighting conditions are a clear sunny day. However, at the beach, the sunny sky and sand may have tricked the light meter in my Minolta X-700. Had I remembered to use the Sunny 16 rule, I might have had better results with this roll of Kodak Ektachrome 100 under these lighting conditions.

The Sunny 16 rule may seem old fashioned in the modern age of auto-everything-what-you-see-is-what-you-get digital cameras. But if your photographic tool of choice is a legacy film camera, many of which either didn’t have light meters or had first-generation light meters that were sometimes inaccurate, the Sunny f/16 rule can help you estimate which camera settings to use for a balanced exposure.

Submitted for the 100DaysToOffload project.

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