Can The Sunny 16 Rule Still Be Used In Digital Photography?

Typical full sun day photograph.  Can you rely on the Sunny 16 Rule?

In film days, we had the Sunny 16 Rule.  The Sunny 16 Rule stated that, with full sun at your back, a correct exposure for any particular film would be 1/Film Speed @ f/16 (or any combination thereof).  ASA was the film speed rating acronym at the time so, 1/ASA @ f/16 would have been the terminology used for film at the time.

For example, if you were using Fuji Provia 100F or Kodak Ektachrome 100 with a manufacturer rated ASA of 100, the "proper" exposure with the sun at your back would be 1/100th sec. @ f/16.  (I won't talk about "best exposure" only "proper" exposure according to industry standards.  That is another post).  If you exposed your film in that manner, you will get a pretty well exposed transparency image. There are exceptions but to keep this simple, I'll just let things stand as stated.

If it was just a bit hazy outside, maybe with some high, thin cirrus clouds but soft shadows, you would open up one stop. If your subject was sidelit, you opened up 2 stops. Shade requires a 3-stop opening from Sunny 16.  The film manufacturers used to include an instruction sheet in every box of film, then to save money, just printed the instructions on the inside of the box as in this Provia 100F example.

You get the idea.  The question I have is—does this same Sunny 16 Rule still apply to digital cameras today? My answer is—Yes and no with my two currently in-use digital cameras as well as with some of my previously owned Nikons.

In February I did some testing to better understand the exposure latitude of the Fuji X-T2 and the Olympus E-M1 Mark II.  I did so on a day with full sun at my back.  Both cameras' base ISO is 200, at which the cameras were set.  I found that the exposure that appeared closest to recording the scene properly, as I viewed it, was 1/400th sec. @ f/8, or in terms of the Sunny 16 Rule, 1/100th sec. @ f/16.  That is a full stop more exposure required than we would expect with the old Sunny 16 rule.  The tests were made using RAW files, not JPEGs. The correct exposure, according to the Sunny 16 Rule would have been 1/200th sec. @ f/16 or, in this case, 1/400th sec. @ f/11.

I've asked myself why would this differ?  I originally thought of two reasons.  First, the winter sun is at a lower angle and is not as intense as the summer sun here in the Northern Hemisphere.  However, I don't think the intensity of the sunshine is reduced by half. Again, I'm looking for anything I can find to account for the difference in exposure requirements.

The other is that the camera makers no longer abide by the old standards, which were set in terms of film speed rated in ASA (American Standards Association) last revised as far as I can tell in 1961 and, the European standard, DIN (Deutsches Institut für Normung). Being these were film standards, the newest rating organization, ISO (International Organization for Standardization) [shouldn't it be IOS?  Go figure?], may have a different standard for digital than the previous standard for film.  I just don't know at this point.

The third reason that comes to mind is that I can recall Fuji engineers addressing the fact that the Fuji cameras' ISO didn't necessarily match other camera manufacturers' ISO in light absorption and subsequent rating. I believe they said at the time there was more than one way of measuring and more than one standard they could follow.  However, since the Olympus and Fuji seemed to require identical exposures in this test case, it seems a) there may no longer be a difference in Fuji cameras now that the X-Trans III sensor is on the market or b) Fuji is using the same measurement standard and nothing has changed since the ISO seems about 1 stop slow and c) Olympus may have gone to the same standard as Fuji, thereby both exposures and image brightness being equal.

At that point, I had put this post aside to wait to continue with brighter sun later in the year.  I'm glad I did because I found something interesting and, I think, significant.

SIGNIFICANT UPDATE:

Last week, I ran the Sunny 16 Rule test once more, but this time with the sun at greater intensity as spring had arrived.  My findings were somewhat the same and somewhat different.  Let me explain.

Test image.  Olympus JPEG straight out of the camera (click to enlarge)
E-M1 Mark II, 12-100mm f/4 lens @ 17mm; 1/1600th sec. @ f/5.6; ISO 200
This is as close as one could come to having the image look like the scene in person and it does
correspond to a "correct" Sunny 16 exposure.  Remember, this is a JPEG file and not a RAW file.  That is key.

Exact same exposure but this is a RAW file straight out of the camera (click to enlarge)
Notice how the luminance is much different even though they were taken simultaneously
using the RAW + JPEG option on the E-M1 Mark II.  It renders this way because this is how
Lightroom interprets the exposure upon import.  It seems Lightroom doesn't record the luminance
in the same fashion as it is actually recorded and "baked" into the file in a JPEG.

This is a JPEG straight out of the camera from the Fuji X-T2, exact same exposure as the Olympus JPEG above.
(click to enlarge)  Theoretically, the two images should be identical in luminance but they are not.  Why?
It seems that Fuji still is not using what we would call the "standardized" ISO ratings as their file require
about 1 full stop more exposure to get the same luminance.  This is a JPEG so the exposure is again "baked"
into the file and not interpreted by Lightroom as would be a RAW file.

Again, the exact same exposure with the X-T2 only Lightroom's rendering of the Fuji RAW file. (click to enlarge)
See text for how much luminance difference I found between the two cameras.

The day was gorgeous with full sun.  I stood with the sun at my back.  I had both my Fuji X-T2 and my Olympus E-M1 Mark II.  Same ISO, shutter speed, aperture, focal length, etc. I shot both RAW and JPEGs.  The JPEG settings were all at camera default in both cameras.  The film simulation for the X-T2 JPEGs was set to Provia, which is Fuji's all around, "standard" film.  The Olympus setting was "Natural."  Everything that could be equalized was equalized.  Additionally, I bracketed by 1/3 stop up and down to have additional files available if needed for comparison.

The reason I tested using both RAW and JPEG was that, over time, my suspicion has become that LIghtroom treats exposure levels for RAW files differently than exposure levels with JPEGs, at least in the cameras I have recently owned.  With RAW files, Lightroom will create an interpolated image, based upon the raw data, for the Library or Develop modules based upon what Lightroom engineers have set that interpretation of the exposure settings to be.  I'm speaking primarily of luminance, with the other parameters being set according to "Adobe Standard", which is the default import "profile" setting under the Camera Calibration menu.

With JPEGs, the settings, including exposure, are baked into the file in-camera.  The luminance is set in-camera and Lightroom reads and displays that level. RAW image files and JPEG image files seem to appear with different luminance levels when viewed in Lightroom.  Hence, my suspicion that something within the engineering of Lightroom CC is amiss. 

After returning home to view these image files in Lightroom, indeed, the RAW files looked very different than the JPEG files.

With the Olympus files, the JPEG made with the Sunny 16 exposure was dead on correct exposure and looked just like the scene.  Brightness was perfect.  (NOTE: exact brightness may not reproduce well here as I don't know what Google does with image files upon upload) However, with the Olympus RAW file, the image shown in Lightroom appeared to be 2/3 stop underexposed.  In other words, I had to increase the Exposure slider in Lightroom's Develop module by 2/3 of a stop to equal the brightness of the JPEG. Why should Lightroom require that?  The exposure data from both files is exactly the same.  In fact, both were made with one press of the shutter.  Shouldn't Lightroom render both identically? 

With the Fuji files, both RAW and JPEG files appeared to be underexposed.  The JPEG file looked too dark and the Exposure slider had to be moved to the right to +0.90 to match the Olympus file. Almost a full stop difference.  The RAW file was a bit worse.  The exposure slider had to be moved to the right +1.06, or about one full stop to equal the Olympus file. Again, why would Adobe engineer Lightroom so two identical exposures in-camera show differently in their Develop Module, albeit less than the Olympus files.

Also, I wonder, if the Fuji files are really underexposed or does Lightroom treat the odd man out, in other words the X-Trans sensor, differently than a Bayer Array sensor?  We all know that Adobe took a long time to improve the demosaicing algorithms for the X-Trans and they still aren't as good as they could be.  So, maybe they aren't treating exposure as well either?  I just don't know.  I'm just speculating right now.

Olympus E-M1 Mark II, 12-100mm lens @ 20mm; 1/800th sec. @ f;5.6; ISO 200 (click to enlarge)
This is very close to reality in how the scene looked as I stood there.

Same scene with the Fuji X-T2, 16-55mm f/2.8 lens @ 34.2mm; 1/550th sec. @ f/5.6; ISO 200 (click to enlarge)
I think 1/500th of a second, or opening 1/3 stop would have better matched these two images.

In further tests, again with RAW and JPEG files, the Olympus files were consistently almost about a full stop brighter than the Fuji files.  That means for equal luminance in your files from both cameras, you have to do one of three things: 1) raise your ISO by one stop with the Fuji camera, 2) lower your shutter speed by one stop or, 3) open up your lens aperture by one stop.  

This tells me, again, that Fuji is utilizing a different methodology in calculating ISO speed than Olympus or somehow Lightroom is treating the X-Trans files differently.  If all was equal, both in-camera and in Lightroom, image files from both cameras would have the same luminance under identical circumstance.

What does this mean for the Sunny 16 Rule?  For me, if my goal is to have properly exposed JPEG image files from my Olympus, I will use the Sunny 16 Rule and will set my exposure accordingly.  If my aim is to utilize the Olympus RAW files, then I will open up about 1/2 stop to get the optimum exposure.  For the Fuji cameras, I will open up one stop from the Sunny 16 Rule for either JPEGs or RAW files as the Fuji seems to gather only 1/2 of the light in any given circumstance as the Olympus.

The bottom line for me is that I no longer fully trust the Sunny 16 Rule for my digital photography.  Instead, as has become my habit, I look at my histogram and judge my exposure by it, rather than EVF image brightness or a past film standard.

Thanks for looking. Enjoy! 

Dennis A. Mook 

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