Ah, a few thoughts about ISO-less

Started Jul 10, 2013 | Discussions thread
Jeff Veteran Member • Posts: 5,087
Re: Furthermore

texinwien wrote:

texinwien wrote:

I touched on this a bit ham-handedly in my last post. Let me try it again.

Let's take the D7000, with a base ISO setting of 100.

Now, let's take a dark scene where we need 1/125 to freeze motion and F/2.8 for sufficient DOF.

For purposes of the exercise, let's say we'd need to use ISO 1600 in Aperture priority mode with the aperture set to F/2.8 to reach a 1/125 shutter speed. It's good to know that we need to use ISO 1600, as it's an indication of the SNR (and therefore of the visible noise) that the resulting image will display.

The other way to state the same thing, without using ISO, is just to dial in 1/125 and F/2.8 in manual mode (and remember, we leave our ISOless D7000 set to the base ISO of 100) and have the camera indicate that the resulting photo will be underexposed by 4EV.

The point, here, is that that ISO number is really just an artificial variable that's communicating to us by how much we're about to underexpose the photo we're about to take. Why communicate that in terms of having to use ISO 1600 rather than just forgetting ISO altogether and communicating that the photo will be underexposed by 4EV.

The second method communicates just as much information without adding the useless and confusing ISO variable to the equation (useless with the D7000, since it's practically ISOless, in reality).

And this pretty funny - many cameras already indicate how much over or underexposure your current settings will lead to, but they include ISO in their calculation.

Talk about confusing. If your camera has a base ISO of 100 and you dial in ISO 800 plus your desired shutter speed and aperture, and the camera indicates that you're about to underexpose by 1 stop, you're actually about to underexpose by 4 stops from the optimum. 3 of those stops are expressed by using ISO 800 rather than ISO 100, and the last is expressed by the camera indicating that you're about to underexpose by one stop.

Why not just leave the camera set to ISO 100 and have it tell you you're about to underexpose by 4 stops from the optimum exposure, since that's what you're about to do? Why split that information into two different numbers? It's not necessary and is confusing to many.

So we're doing the same thing.

  • We monitor the distance from optimum exposure. You measure it logarithmically in f-stops. I measure it arithmetically in ISO.  
  • When maximizing exposure I call it working at base ISO and watching for blown highlights. You do the same thing.
  • When working in poor light (e.g, shooting indoor sports) you're working three variables -- underexposure, aperture, shutter, I'm working three variables -- ISO, aperture, shutter. If we're visualizing the image the same way, then the noise constraint forces us both to the same aperture and shutter choices. 

I come from a background in optimization and control theory.  In that framework, what we have here are three variables to choose (aperture, shutter, call it degree of underexposure if you like) and a number of constraints including a hard saturation constraint and a soft noise constraint. When one or the other of those constraints is active then you no longer have three independent choices because they are coupled by the active constraint.  In your ISOless formulation, you haven't changed the nature of aperture and shutter, so its relabeling the ISO knob as something else -- call it gain, stops of underexposure, whatever.  It's a distinction without a difference.  At the noise constraint they are again coupled in the same way.  In the range in between you have independence of the three variables, but that region is a relatively narrow 3-4 stops with larger format sensors, and nearly zero for small formats.

With regard to read noise, amplifiers, etc.  Why should I care?  If the engineers have done their job, then they'll have optimized the design for image quality under optimal and adverse shooting conditions, regardless of how you or I choose to measure the distance from full exposure.  Frankly, I'd prefer that the engineers ignore your advice and simply deliver the best possible image response under adverse shooting conditions, whether that's called high ISO or degree of under exposure.

With regard to the interface, now there you have a point. The separate EC dial and ISO dials, in fact, are redundant at first glace. I don't know if they are actually identical under the skin, but wouldn't be surprised if they were.  I don't happen to find the math -- ISO 800 and EC+1 = ISO 1600 very difficult, but agree that one could safely lose one or the other, the EC knob or the ISO knob.  BUT NOT BOTH!  Just like I want the camera to handle that saturation constraint by coupling aperture and shutter, I want to be able to specify that same linkage for the soft constraint of noise.

In the end, with current technology sensors in larger formats, you have maybe 3-4 stops of relative flexibility with underexposure (or more conventionally, acceptable ISO).  In smaller formats you much less.  This is still the most constrained of the three variables (aperture, shutter, ISO/underexposure).  Until sensor technology catches up and produces a wider range of exposure flexibility, I really don't see ISOless as an innovation.

Sorry, but this all strikes me a distinction without a difference.

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You don't make a photograph just with a camera. You bring to the act of photography all the pictures you have seen, the books you have read, the music you have heard, the people you have loved.” -- Ansel Adams

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