Estimating Exposure Outdoors sans Light Meter

pathfinder

Estimating Proper Exposure without a Light Meter Out of Doors


Some new digital photographers seem to have difficulty believing that you can shoot a digital camera in manual mode outdoors for most of the daylight hours without using a light meter. After all, new digital cameras all have light meters and automatic exposure modes built into them.
But 70 years ago, folks were shooting Kodachrome transparency film without any light meters. Kodak's Kodachrome was very intolerant of incorrect exposure. Modern digital cameras are similar in their requirements for correct exposure, but may be more forgiving than Kodachrome.

I did a review of “Bound for Glory - American Color 1939-1943” - a book full of images of Kodchrome that were probably shot without a light meter. Kodachrome is very unforgiving of improper exposure - maybe 1/2 stop of light too little or too much and the slide was ruined.

This was shot in 1945 without a light meter - I know, because this is shot of your author age 1 in Fort Sam Houston Texas.


The focus wasn’t too good, but the exposure wasn’t off by much. How did my father do that??
Rather than a light meter, he almost certainly used the rule known as the “Sunny 16”, which lets you estimate the exposure between 10 am and 5 pm accurately, without a light meter. You might ask why this is worth wasting your time on today when you already own a excellent meter in your camera.

The answer is that, even today, meters can give the wrong exposures, and it is always good to be able to estimate the correct exposure in your head without any tools but the understanding of the Sunny 16 rule.

Light meters get fooled when asked to meter very bright objects such as a snow covered landscapes, or a shot of the moon, or a very dark object like a black labrador retriever. The reason meters get confused is that they assume everything in the area metered is a neutral mid range tone and then read its reflectance - the so called 16% grey card, but in the real world things are not always medium tones.

The sunny 16 rule is based on INCIDENCE lighting, and will frequently be more accurate than most reflected meter readings that depend on the reflectance of the subjects. Incident metering does not depend on the subject, only the intensity of the lighting.

The Sunny 16 rule is based on the fact that the sun is equally bright everywhere outdoors between 10 am and 5 pm. So, if you know what the exposure is for sunlight at mid-day, then you can estimate it for cloudy or overcast situations.

The rule states that the proper exposure is determined by the ISO of the film/sensor setting. We will assume ISO 100. For ISO 100, at mid day with sunlit mid-toned object, set the aperture at f16, and the shutter speed at 1/ISO or 1/100th ( if your camera does not have a shutter speed of 1/100th, a setting of 1/125 if good enough for government work.)

Knowing this basic exposure allows us to draw up the following table based on exposure values


Notice that the table shows values for ISO 100, 200, and 400. If you have ISO 1600, then f16 at 1/1600th is the correct exposure. Then, by equivalencies, the rest of the table can be constructed

f16 1/1600
f11 1/3200
f8 1/6500
f5.6 1/13000

But there are no consumer cameras with shutter speeds this high, so you will need to dial back the ISO in bright sunlight.

But, what if the day is not bright sunlight, but cloudy?? Then, the light is described by the shadows seen, or not seen.

Soft shadows, easily seen with soft edges is weak, hazy sunlight and needs 1 stop more light or f11 rather than f16 at 1/ISO.

Cloudy bright days refer to days where shadows are barely visible, and they require 2 stops more light or f8 and 1/ISO.

Overcast means NO SHADOWS and requires 3 stops more light or f5.6, the same as in the shade on a sunny day.

This knowledge can be very helpful.
One example that comes up frequently, is people trying to shoot shots of the moon. They point their camera, in an automatic mode, at a black sky with a small, bright, white moon, and find out that the moon is not exposed correctly at all.

The moon is a sun lit object - just like a car sitting on the street at noon - and the exposure should be very close to the same even though the moon is very distant.

So, for ISO 100, the settting would be f16 at 1/100th. Or we could open the aperture two fstops, f16->f11->f8 , and shorten the shutter speed up two stops 1/100th->1/200th ->1/400th and shoot at f8.0 at 1/400th at ISO 100.
I found this image I shot last fall in my gallery.



Note the exposure data - ISO 100 f8.0 1/400th - Guess how I chose those settings???...
Just as predicted by the Sunny 16 rule. Now does this seem worthwhile to know??

Here are a couple more examples I have just pulled randomly from my galleries.

Here is an image that is hard for meters do deal with - bright, sunlit snow. - Indeed, I dialed in +1.33 Exposure compensation to help the meter read this scene - and it was shot with at f11.0 at 1/40th at ISO 100. Sunny 16 gave f11, 1/50 at ISO 100. Not too shabby.



Here is another very brightly lit snow field at 10,00 feet - not a cloud in the sky
EXF data -> f8.0 1/500th at ISO 100 Sunny 16 -> f8.0 1/400th at ISO 100 - pretty close




Here is another image - shot in a cloudy day with barely visible shadows calling for 2 stops more light than bright sunshine at 7500 feet in Wyoming

EXIF-> ISO 400 f5.6 1/1000th Sunny 16 suggests two stops more light than sunshine or f8 at 1/400th for ISO 400, or f5.6 at 1/800th Again - pretty close!!


Again, the horse's shadow is barely visible, shot at 7000 feet in Wyoming,- add two stops - EXIF -> ISO 400 f11 1/200th Sunny 16 suggests ISO 400 f11 1/200th Again it seems to work .


I hope I have demonstrated that the Sunny 16 rule is easy to understand, and can be very helpful in understanding exposures needed and in intepreting your cameras exposures properly.

Andy

pathfinder

Thanks Boss. :

Any suggestions for improvement??

saurora

I once had this formula written down in my notes...many, many years ago. Since moving away from serious photography for a large part of my life, alot of what I had learned has been forgotten. Thank you so much for refreshing my faded memory!!!! This is a very helpful formula to recover!

pathfinder

:

DavidTO

pathfinder wrote:

Thanks Boss. :

Any suggestions for improvement??

How about we put it on our tutorials site? Now *that's* a good idea!

pathfinder

OK by me:):

wxwax

Outstanding. Thanks for taking the time to write this up.

pathfinder

I really thought everyone knew this

wxwax

pathfinder wrote:

I really thought everyone knew this

I've read it many times, but I'm lousy with numbers :uhoh and don't remember it well. And I don't think anyone's written it up comprehensively on dgrin before, which is why I copied it into the Hall.

saurora

It's a memory thing....not a math thing. It's like a foreign language. Use it every day and no problemo. Stop using it for a while and it becomes like all those phone numbers of friends and family that you once knew, but since the advent of cell phones with memory storage...who knows anyone's phone numbers? I'm going to print this and read it everyday until it "sticks"!!! It is very helpful to know (...as I recall...)

JonMikal

i've used the "16" rule for years...glad to know others still do. you provided an excellent totorial

thanks for sharing!