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The exposure required and Sunny 16 Rule

See also Exposure

Today we have cameras with a number of built in meters, plus some use hand meters or use Exposure Targets  in conjunction with either their camera meter or handheld meters. In addition to this we have after the image capabilities to check in the back LCD panel what we have taken, look at exposure curves, and more.

Historically, well until film, after 35mm became available, the majority of photographers did not have a meter, yet many were able to get exposures at least as accurate as the majority of photographers do today.

This was and still is possible as the variable components, sensitivity (ISO ), Shutter Speed and Aperture are all able to be adjusted in a way where a change to one can be counterbalanced by a change in either one of the others. So for example you can let in twice as much light for half the time.

The start point used before meters, was often the Sunny 16 Rule, this says that on a sunny day if you set the sensitivity (ASA or ISO) to the shutter speed then the aperture required is F16. Young men were told you can easily remember the number 16, its the age of consent.

If it was slightly overcast you allow 1 more stop of light, F11, Overcast allow 2 stops F8, heavy overcast 3 stops F5.6. You can determine which of these conditions apply by looking at the shadows produced.

Sunny 16 Rule

ISO set to shutter speed


light condition






Slightly overcast

Soft around edges



barely visible


Heavy overcast

No shadows

As we can vary any setting from this point by making the counterbalancing change to another variable we can select the variables that will give us the results we want. Lets take an example, an overcast day we know at ISO 400, we can set the shutter speed to 1/400 and the Aperture at F8 to get a good image recorded. If we want to increase the aperture by two stops to F16 (smaller hole, less light) to get more depth of field, we can simply change the shutter speed by two stops as well (slower speed, more light) so 1/100 second at F16.

Both ISO and shutter speed are easy to convert to stops and back as they half or double the number,  so for example 1/400, 1/200, 1/100 are shutter speeds all 1 stop apart from each other.

Aperture is a little different in that we have to look at a hole allowing light in, like a pipe allowing water to flow, so the number doesn't make as much sense. The result is that doubling or halving the number is two stops instead of 1.

So F stops go F1, F1.4. F2. F2.8, F4. F5.6. F8, F11. F16, F22, F32

On top of this we could allow a stop or more for back lighted subjects, and make other adjustments.

To save doing all this in your head you could use an EV table where 1 EV = 1 stop.

Using an EV table, such as the Camera Images created one that is a 2 sided laminated A4 sheet folded into three, you can look up the light under most conditions that apply, and using the table look at the corresponding options to use ISO, speed and aperture, plus do simple changes to allow for Neutral Density filters, Teleconvertors  and other items.

Today most routinely use Exposure Meters, but understanding how to set exposures without a meter, working it out for you is a major advantage towards gaining control, and getting the results you require.

 <<  ^  Exposure Article Route   ^  >>    Exposure with an Exposure Meter

for details on exposure article route see the Exposure  page


By: Keith Park   Section: Exposure Key:
Page Ref: exposure_required Topic:  Exposure  Last Updated: 08/2009

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