Is It Time to Abandon the ISO Scale?

by Peter Zack


I pose this question for a couple of reasons: The ISO scale is 1) misleading and 2) misunderstood. I would be surprised if manufacturers pushed to adopt a new scale though. More is better, right? If brand X can shoot at ISO 6400 and Brand Y can shoot at ISO 12,800, then Brand Y must be, like, 6400 times better or something. Right? Nope it’s only 1 stop. The ISO scale was developed in the film days and as far as I’m aware, the fastest film available (other than maybe some specialized scientific films) was Kodak T Max at 3200. Digital sensors have far exceeded that today.

Aaron Johnson's What the Duck

While not exactly on point, I think the cartoon sums up part of what I feel is a misleading issue. The cartoon does make light of the technical understanding of ISO. Have you ever read the WiKi article on that subject? Even my eyes glaze over. I am willing to bet that a lot of shooters (I’m guilty of this) have set the camera at ISO 4000, thinking they gained a lot of sensitivity but not as much noise as 6400 gives them. Well not really. That’s only 1/3 of a stop and they really gained very little in shutter speed, just lost some detail and increased the noise a bit. The 1/3 boost in shutter speed certainly isn’t going to make much difference in freezing the action in low light. Other choices, a tripod, faster aperture, adding a flash or more light etc, shot at a lower ISO, would create much better photos in many situations.

From here on I’ll drop the ISO part, assuming you know what I’m talking about.

The scale makes no sense with today’s sensors and the ones coming in the future. We already have cameras that can shoot above 100,000. Who knows where they will be 2,3, 4+ years from now. Shooters at all levels of experience may not understand the sensitivity steps, make the wrong choice in a hurry, or get a little hoodwinked at how much extra latitude you get from 6400 to 12,800 because the number sounds so much bigger than it really is. Think in terms of salary: If you make $51,200 a year and the boss offers you a new job at $102,400, that’s a huge leap. Your entire life just changed. Well that’s how we think; we don’t see that it’s just one stop faster.

The Nikon D3s can shoot at ISO102,400 which one site loudly proclaimed has, 'Night Vision' and 'ISO 102,400. Yeah, that's a six-digit ISO.'

Is one full stop a big deal? Sure it is, shooters go nuts to buy a lens that is 1 stop faster. Also, the scale is exponential. So 200 is twice as sensitive as 100 and 400 is 4 times as sensitive as 100. In terms of what you can do with that 1 stop, It means you could shoot at 1/60th at 1600 and 1/125th at 3200 and get the same exposure results. That could be the difference between stopping the action and not while taking family photos indoors. In my thinking though, if the scale was more straightforward, people would understand better what they gained when going from 3200 to 6400. Sometimes, that one stop and added noise might not be worth the trade-off for a faster shutter speed.

I’d suggest a new scale that really reflects the steps and gain as you turn up the dial. Plus the smaller numbers would be much easier to display in the viewfinder. This way, you can better understand the advantage and relationship with the other 2 parameters, shutter speed and aperture. This would really benefit new buyers, people who have never shot film or who moved from a point and shoot to a DSLR for the first time and never really considered ISO before.

My hope is that some day, sensors will natively go below 100. I really miss how incredible Kodachrome 25 was. So I suggest the scale start at 1 which would equal 100 now and consider the possibility of even lower sensitivities. Then if we get ISO’s below 1 (100) the scale would show a negative. Further, the scale would need to be similar to the aperture scale. for half and 1/3 settings.

Maybe something like this, reflecting 1/3 and 1/2 adjustments:
ISO 12, 25, 50, 64, 80, 100 = -2, -1, 0, 0.3, 0.7, 1.0
ISO 100-200 = 1.0, 1.3, 1.5, 1.7, 2.0
ISO 200-400 = 2.0, 2.3, 2.5, 2.7, 3.0
ISO 400-800 = 3.0, 3.3, 3.5, 3.7, 4.0
ISO 800-1600 = 4.0, 4.3, 4.5, 4.7, 5.0

So then your basic scale is 1, 2, 3, 4, 5 etc. If 100 = 1, then 102,400 would equal 10. We’ll call it the EtL scale. Simple and straightforward. Fractional steps would directly correspond to 1/2 or 1/3 step adjustments to your shutter speeds. I think a much less confusing and more logical way to display your shooting information in the viewfinder. You instantly realize that you’ve only gained a stop and may be better to open the lens up a stop, or decrease the shutter speed when you can, to get a cleaner image.

Cheers and good shooting. –Peter Zack

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  1. Interesting idea. I agree with your prediction that the camera companies probably will not adopt this. Marketing those big numbers seems to hold some perceived value. I think we could end up opening up a can of worms here, though. Unless all companies agree, or there is some sort of registered standard, such as ISO …
    Quick side note: missing from your article is that ISO stands for International Organization for Standardization. In the most basic terms, the Photographic community turned to the ISO to establish a set of standards for the ratings of film sensitivity.
    … Short of another round through the ISO committee, establishing the EtL scale of 1.0 = ISO 100, I don’t see this working out well. What’s to stop a company from using the new EtL scale, but, somewhere in the fine print, list that EtL 1.0 = ISO 200, or ISO 50, or whatever?
    A secondary issue, adding further confusion to the whole topic, is that there is evidence that there is variance in what might be called ISO 100 according to your digital camera – some cameras’ ISO 100 is test out the be slightly more or less sensitive then true ISO 100.

    I would suggest that anyone who can understand how aperture values work can understand how ISO values work equally as well. (who knew that 2×2.8 = 4???) And, while I have certainly fallen prey to confusion in the numbers game between f-stops, shutter speeds and sensitivity (and the EtL scale would certainly simplify things), I still hold that you have to be smarter than the equipment you are working with.


  2. Ah Sean, who said I was smarter than my equipment???? :)
    I know this would never happen but enjoyed your comments. One of the things that caused me to consider this is the display in one of my cameras has 4 digits to display ISO. There’s no room for more as the display is full of data. So going over 5 digits, ISO is displayed “512K” or 128K. In a hurry, this is confusing when your EV adjustments are set to 1/3 increments. So a simple 2 or 3 digit display might be much easier.

    I agree that all metering systems are not created equally. Some are as much as 20% +/-. But no matter what the scale, this will always be the case.

  3. Just a point of history:
    Until the 70s, ISO was called ASA (American Standards Association=ASA).
    In addition, outside the USA, film speed (sensitivity) was rated both in ASA and in DIN (originally German: Deutsches Institut für Normung=DIN).
    DIN was a log scale whereas ISO (ASA) is an arithmetic scale of a log phenomenon (this is why one step separates 100 from 200 ISO, another step separates 200 from 400 ISO, etc.).
    Whereas in DIN, 100 ISO=21°DIN, 200ISO=24°DIN, 400ISO=27°DIN, etc.): + 3° for each doubling of the sensitivity.
    ASA rating was proposed by the US and accepted by the rest of the world (those members of ISO): therefore ASA became ISO.

    All this to say that … fifty years ago we had already a measurement method which was less misleading: the DIN.
    And all this to say also that I agree with you that ISO, even if it corresponds to the “truth” of the film (and human) sensitivity, may be misleading for the public.
    By the way human beings perceive and react not only to light in a kind of logarithmic way…

  4. Ariel, you are absolutely correct and I’d forgotten that I had an old light meter that read DIN scale. Makes much more sense. I learned on the ASA scale and forgotten DIN which was the standard for some time and much more logical. Thanks for the reminder. Maybe we should go Back to the Future….

  5. Going “below” 100 is pointless with digital as you cannot get below pixel density resolution. The ISO is not a standard of resolution but of SNR, or gain. Digital sensor ISO is interpolated from the old ISO film standard as a benchmark. It is not based on an objective “grain” or SNR scale.

    Most digital sensors use ISO adjustment to alter alter the gain, but at a loss of contrast below their baseline; or SNR noise above. If we start asking for ISO 50 again, we’re into Spinal Tap “it goes to 11″ territory.

  6. No camera sensor can actually shoot at 12800. Most also cannot shoot at intermediate ISOs.

    Actual amplifier settings are 100 to 3200 for most current Canon models (6400 for the 1D) and 200 to 3200/6400 (depending on model) for Nikons. Everything else is done through scaling in firmware, which can easily be verified by plotting a histogram of raw data – e.g. 6400 on a Canon 5D only contains even values and results in a “comb” graph.

    As for ISO, it’s meant to be both measures: ISO100/21°. Camera manufacturers simply omit the included DIN value.

  7. “If you make $51,200 a year and the boss offers you a new job at $102,400, that’s a huge leap. Your entire life just changed. Well that’s how we think; we don’t see that it’s just one stop faster.”

    This is plain silly. Salaries are linear, film speed is not. It’s a shame that it is too much to expect people to be able to comprehend a logarithmic scale. Viva la digital revolution!

  8. Peter, I get what you’re saying but this could have been done a long time ago for shutter speed or aperture as well. Doesn’t the difference between 1/2000 and 1/4000 *sound* like a much bigger difference than 1/125 -> 1/250? And photographers have sort-of learned to deal with the aperture scale as well.

    I can see how it might be a nice option to have but the point of standards is that they are standard–my lightmeters, flashguns, and all my cameras ‘speak’ the same language. I know when I pick up a Sony NEX camera and adjust shooting parameters for depth-of-field along a scale labeled only as either more or less depth-of-field I don’t like not really knowing what it’s going to do. Admittedly your suggestion is more practical than that.

    One can also compare your change with the industry convention for expressing exposure compensation–when exposure compensation first became more common in the late 70′s/early 80′s, exposure comp dials were labeled 1/4x, 1/2x, 1x, 2x, 4x. A few years later they started showing -2, -1, 0, 1, 2–I’d guess most of us are more comfortable with this now. I suspect this is at least in part due to the relative awkwardness of the first system for expressing fractional stops.

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