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| Old Truck. Great Smoky Mountains National Park, Tennessee. (click to enlarge) Fujifilm X-T2; 16-55mm f/2.8 lens @ 42mm; 1/125th sec. @ f/8; ISO 640 |
Recently, while conducting my tests to determine what actual resolution differences I could see in a Fujifilm X-H2S 26mp image file to an identically composed Nikon Z7II 46mp image file, I noticed that to achieve the same level of luminance, in other words, to make both image files look the same brightness in Lightroom Classic, the Fujifilm image file needed more exposure. Exactly 1.07 stops more exposure, in fact. But that shouldn't be news to long time Fujifilm camera users.
This exercise did bring back some memories I had from several years ago about Fujifilm and Olympus rating their ISOs differently than other camera manufacturers. I remember reading that there were two common ISO standards that manufacturers could use. With seemingly Fujifilm and Nikon using two different standards, does it really make a difference?
When I was a film shooter for 30+ years, often times I used the Sunny 16 Rule to determine proper exposure. If you are not familiar with that rule, roughly it states that when the sun in a clear blue sky is at your back (and I'll add is a reasonable distance above the horizon that I'll interpret to be after 10 a.m. and before 4 p.m. on a summer day), that the correct exposure for your photograph would be 1/the film's ASA @ f/16. ASA (and DIN) instead of ISO was how film speed was rated back then. For example, if you were using a film with ASA 125, your correct exposure, using the Sunny 16 Rule, would be 1/125th sec. @ f/16. From that basic exposure you could then change to other equal apertures and shutter speeds to better suit the scene and situation in front of you. It was a very reliable method of achieving correct exposure if you didn't have a light meter.
But this rule doesn't seem to hold true for many digital cameras? Can we count on the Sunny 16 Rule when photographing with our digital wonders? Using my Nikon Z7II and the Sunny 16 Rule, my exposures were perfect. But using the Fujifilm X-H2S, they were dark. As I mentioned, a full stop dark. But should you even worry that your Fujifilm camera seems to be "underexposing" your images? In my opinion, no.
On a clear day with the sun at my back, I made a few identical images with both of my cameras, using identical settings. The cameras were set to Manual Exposure, the same shutter speed, the same aperture, the same ISO and the same full sun White Balance. I used a relatively neutral film simulation/picture control setting. The exposures were made using the JPEG format instead of RAW as I found different editing software programs are engineered to convert RAW files differently. For example, have you ever opened up your editing software and looked at RAW files next to their partner identical JPEGs? Often times the exposures look different. JPEGs are processed in-camera while RAW files are only getting instructions from the camera as to how they are supposed to look. It seems to me the best way to eliminate any outside variables for how a photo appears in Lightroom, On1, Capture 1, DXO PhotoLab, etc., in-camera JPEGs take out those variables and reflect the cameras' actual settings.
Even though, at identical settings, my Fujifilm X-T4 and X-H2S image files appear 1 stop darker (needing double the light or double the exposure values) to appear identical to my Nikon Z7II image files, I don't think it really matters.
First, the dynamic range of digital sensors today are so good that almost never can you not make a good exposure just by pointing and shooting and not worrying about what settings your camera's meter has set (exposure-wise). In the past, I did numerous tests with Nikon, Fujifilm and Olympus cameras and, with just a few exceptions for a small amount of blown highlights, the light meters in my cameras were so good, that I really didn't need to crank in any exposure compensation. Even though the Fujifilm files are 1 stop darker, that is relatively meaningless, under most circumstances.
Second, when shooting RAW files, the ISO setting in the metadata of the image file is just an instruction to your editing software as to how to render the file. It is not a hard and fast setting. Higher ISOs don't do anything more than, in effect, 'turn up the volume' and amplify the digital signal generated by the sensor.
Third, it seems nowadays, most sensors in digital cameras are ISO-less. In practical terms that means that, in one example, if you set your camera for an exposure using ISO 1600 to 'properly' set your exposure, you also can set it to ISO 400, then increase the exposure slider in your editing software the equivalent of stops and the differences in the two files will be none or very, very minor. ISO numbers, in and of themselves, sort of become meaningless or maybe just a handy reference number.
If all of this is too technical, the bottom line for me is that even though the Fujifilm files are one stop darker than my Nikon files when viewing them in Lightroom Classic, that is actually meaningless when it comes to the final edited image. If anything, it is a benefit since Fujifilm's exposure and ISO algorithms seem to have an underexposure bias, thus giving us a bit more headroom in not losing any highlight detail.
Now, I am not an optical engineer nor an expert in ISO standards, etc. and if I have misstated anything, please correct me. But I believe what I have stated is pretty accurate.
All that said, there are things you can do to 'optimize' your image files when it comes to exposure. My best advice for achieving the best exposure for any brand digital camera is to pay attention to the histogram and moving it as far to the right as you can without clipping the highlights or the graph hitting the right edge. Then you can re-adjust your exposure, highlights and shadows in your editing software. That way you don't have to 'lift' the shadows which causes some digital noise. That is the old ETTR rule. Expose To The Right.
Frankly, if you don't want to be bothered by that, then just keep all of the graph's data within the left and right histogram edges and you'll do pretty well. Again, our photo tools are so good today that the photos almost take themselves! LOL
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Thanks for looking. Enjoy!
Dennis A. Mook
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Very informative. I think of the critical exposure requirements from the film era. You had better be accurate in those years when using transparency film. And very close for any panchromatic film.
ReplyDeleteWith current cameras, if the acceptable limit for a highlight overexposure is not exceeded, the image file will be usable in most situations.
I find the Zone V exposure for my Olympus camera to be greater than that of the Nikon, similar to your Fujifilm experience. I find that a curiosity, but it doesn't matter much in making photographs. I wonder why the imaginative marketing arm of Nikon hasn't found a way to exploit that.
When the subject permits, I utilize the advice gained from reading this blog and make a second exposure of 1-2 stops more when there is important shadow detail or an anticipation of shadow noise.
Thank you for your thoughtful comment and thank you for your kind words. I shot with Olympus from 2013 until last year and they rate their ISO the same way as does Fujifilm. I don’t know how Canon or Sony rate theirs.
DeleteWith slide film it was best to underexpose about 1/3 stop to not lose the highlights and with negative film, I overexposed up to one full stop to capture all of the shadow detail. Digital is a different world.