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I've heard of the "Sunny 16" rule. What is it? How, and in what situations, can I use it?

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    \$\begingroup\$ I'm really surprised this doesn't exist already, but I know you have quite the google-fu on what does & doesn't exist on here. Looking forward to the self-answer which I can feel is coming :) \$\endgroup\$
    – Tetsujin
    Commented May 31, 2020 at 8:04
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    \$\begingroup\$ I was also extremely surprised. I also want to see other's answers before I post one. If one of them hits the nail on the head, I won't have to write one. \$\endgroup\$
    – Michael C
    Commented May 31, 2020 at 8:12
  • \$\begingroup\$ See Wikipedia. Also shows how you can tell it's "not sunny" by looking at shadows (or lack thereof). \$\endgroup\$
    – xenoid
    Commented May 31, 2020 at 12:45
  • \$\begingroup\$ @xenoid The problem with the Wikipedia page is that it assumes distinct shadows always require f/16. Near the equator during midday, that could be the case. In Finland? Hell no! I have been in many situations where the proper exposure is way below f/16, the shadows are distinct and the subject is in sunlight. I suspect the cause is air mass effects: in northern latitudes, sunlight has to travel through more air mass than at the equator. \$\endgroup\$
    – juhist
    Commented May 31, 2020 at 12:52
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    \$\begingroup\$ @Juhist All that means is that the "Sunny 16" rule is a "Sunny 8" rule when above 50° of latitude. OTOH this is "rule of thumb", that doesn't try to be too accurate, and may be more suitable to film than to digital. \$\endgroup\$
    – xenoid
    Commented May 31, 2020 at 12:56

2 Answers 2

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The sunny 16 rule explains that the proper exposure in non-obstructed sunlight traveling through minimal air mass is f/16, and shutter speed set to the reciprocal of ISO sensitivity.

For example:

  • If you want to use 1/200 s shutter speed because of the reason that it's the camera's fastest flash sync speed and you don't want to / can't use high speed sync, you need to set f/16 and ISO 200. If you want more background blur, you could move from this one f-stop away to f/11 and ISO 100. If the camera has ISO 100 as its base ISO, you cannot move further to f/8 and ISO 50.

There are several failures of the sunny 16 rule:

  • It works only in very narrowly defined conditions. Any clouds? You can't use it. Subject in shadows? You can't use it. Sun not well above the horizon? You can't use it. Those knowledged in photovoltaics know that atmosphere has an air mass effect: light of sun close to horizon has to travel through more air mass than light of sun directly over your head. This air mass effects affects photography equally well.
  • It assumes that the camera's ISO sensitivity is accurate. Very often, it is not. If you set ISO 100 and 1/100 s shutter speed, you may get something close to ISO 100 but not quite ISO 100.
  • It assumes that the lens has certain transmittance. One lens at f/16 and lots of glass elements (e.g. zoom) may transmit less light than another lens at f/16 and little glass elements (e.g. prime).
  • It requires you to do calculations in your head if the aperture you want to use is something else than f/16. Want to use f/8? Set four times faster shutter speed. Want to use f/4? Set sixteen times faster shutter speed.
  • If you have a crop sensor camera, f/16 results in more diffraction than optimal. Limiting yourself to f/8 would be far better.
  • Even with a full frame camera, an aperture as slow as f/16 can cause dust on the sensor to become more visible than at faster apertures.

Because of the numerous failures, in this era of autoexposure, I would use sunny f/16 rule only as an estimate for correct exposure and estimate for power needed for fill flash in sunlight. Let the camera's autoexposure meter do its job. It probably does the job far better than someone blindly following the sunny f/16 rule.

My experience photographing in sunlight in a northern country where sun is not often very high, is that the conditions where sunny f/16 rule applies are far more rare than the conditions where sunny f/16 rule does not apply.

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    \$\begingroup\$ In the UK if I need to guess an exposure outside I tend to assume f8, and reciprocal iso, it's very rarely bright enough here for sunny 16 to work. I've seen it work in places like the canaries, but frankly it came as a bit of a surprise when I realised my camera was auto exposing on the sunny 16 line. \$\endgroup\$ Commented May 31, 2020 at 12:33
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    \$\begingroup\$ If you need the "Sunny 16" rule, then that probably means you don't have a light meter, and that probably means that your camera doesn't have a light meter, and that probably means that it is not a digital camera, in which case, you don't exactly set the ISO. It'll be more practical to check what ISO film you have loaded, and then set the shutter speed accordingly. \$\endgroup\$ Commented May 31, 2020 at 14:11
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    \$\begingroup\$ It's not a failure, it's a starting point :) \$\endgroup\$
    – hobbs
    Commented May 31, 2020 at 22:10
  • \$\begingroup\$ One way I used it when I still had a film camera was to assist in getting the exposure right in situations where the lighting can change and I need to take a picture quickly. I'd set my camera using the Sunny 16 rule, and then wait for the scene to present. Then, I'd adjust the exposure using the light meter like normal. However, by anchoring myself to Sunny 16, I started with settings and a mindset which was roughly correct for the situation at hand, rather than frantically trying to figure out what sort of balance I wanted to find and missing the shot due to my inexperience. \$\endgroup\$
    – Cort Ammon
    Commented Jun 1, 2020 at 17:28
  • \$\begingroup\$ @CortAmmon I'd love to see and upvote that in an answer, where it belongs. Please put your answers in the answers section, even if they're short and Criteria for determining if a post should be a comment or an answer Thanks! \$\endgroup\$
    – Michael C
    Commented Jun 2, 2020 at 11:16
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Roll film box had instruction sheet and or this exposure aid was printed on the inside of the box. enter image description here

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  • \$\begingroup\$ This indeed shows that sunny f/11 applies very rarely. f/11 1/125 ISO100 means approximately f/13 1/100 ISO100. Two third-stops below f/16. \$\endgroup\$
    – juhist
    Commented Jul 24, 2023 at 19:02

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