i watched a video on pray pixel about a street photographer with a Leica film camera. So I read a bit about the mechanical Leica, and it said there was no built in light meter. Hailing from the DSLR era, how would one have calculated their exposure triangle without the advent of a built in, or hand held light meter?

  • \$\begingroup\$ Leica did make clip-on meters for some of the M models. \$\endgroup\$
    – inkista
    Jun 11, 2015 at 6:42
  • \$\begingroup\$ FWIW: At school we were told that when in doubt, f/8 at 1/50" will almost always get you something. (on film) \$\endgroup\$
    – Stan
    May 11, 2016 at 18:20

2 Answers 2


What you're looking for is the Sunny 16 rule.

The wikipedia page is good enough; however, all of the SE sites don't like you to dump a link and leave. So, I'll just rip the rule straight from the page.

Since you know the exposure triangle, it boils down to: at ISO 100 you use f/16 and 1/100s on a sunny day to get a properly exposed picture.

With that as a basis, you can adjust yourself through stops to get the same exposure at ISO or at f/32.

Although there was a time prior to hand held light meters, they are pretty darn old...mine is from the 1940's and still works just fine. In face it is better than the built in one on my AE-1.

  • 1
    \$\begingroup\$ i'd add following: shooting on film (namely, BW negative) you have option to pull or push your exposure when printing. Film has wide dynamic range, thus you need to mis-expose a lot (more than 3 stops) to really lose shadows or highlights. Briefly, if you make 1-2-3 stops mistake, printing will tolerate it. \$\endgroup\$ Jun 11, 2015 at 5:39
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    \$\begingroup\$ What about when it wasn't sunny? \$\endgroup\$
    – mattdm
    Jun 11, 2015 at 10:46
  • \$\begingroup\$ For non-sunny days there are a number of modifiers to the basic sunny 16 rule, most of them have you judge how distinct the shadows are as a way to guess the amount of light you have. I've also seen modifiers for outdoor side and back lighting. Back in the day I've shot slide film (less forgiving in terms of bad exposure) with good results. In photographic terms, the sun is a pretty consistent light source. \$\endgroup\$ Jun 11, 2015 at 11:58
  • \$\begingroup\$ Ok, I have heard of the sunny 16 rule, and just supposed there was always something more formal, or a formula could use to calculate the exposure from some measurement of the ambient luminance. \$\endgroup\$
    – user74091
    Jun 11, 2015 at 14:21
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    \$\begingroup\$ @user74091 If you have a way to calculate foot-candles or lumens per square meter then there is a chart that will tell you your exposure settings. That's all a basic light meter is: a foot-candle detector and a formula. I don't know what the formula is, but it should be easily figured out by looking at a light meter. \$\endgroup\$
    – SailorCire
    Jun 11, 2015 at 14:53

Here is the photographic formula for the calculation of exposure used for photographic emulsions. Electronic ISO speed designations used today is an approximation of the earlier ASA speeds derived in the early 1930s. For all intents and purposes ASA and ISO are interchangeable.

The f/# = sq. root of ASA
shutter speed = 1/(candles per sq.ft.)

Such exposure would produce a patch with a density (with standard sensitometrical processing) of 0.301 over base plus fog density. Plus or minus : ).


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