Re: ISO for beginners

Well its a thread called "ISO for Beginners" and it's posted under a category called "Beginners Questions". So I'll have to disagree with who is confused here Jim, sorry.

Yes, there are many ways of implementing ISO. My belief is that a beginner does not need to understand the detail of any particular implementation in order to understand the overall concept of ISO.

A car analogy might be the gas pedal. Conceptually, when you push the pedal down, the car goes faster. The further down you push it, the faster the car goes. One does not need to understand automatic transmissions, or direct drive electric motors in order to understand the concept, nor does one need to understand it in order to be a very good driver. Obviously, this doesn't tell the whole story. There is generally an upper limit on how fast the car can go, head winds, tail winds, and hills might also alter speed, even if the gas pedal is help constant. However, for someone first learning to drive, the idea that pushing down on the gas pedl makes the car go faster, is an incredibly useful overview.

Now, if you are trying to absolutely maximize some aspect of your car's performance, it can be helpful to understand what's happening under the hood. But a beginner driver does not need to know these things.

When it comes to Digital Camera ISO Speed, the absolutely correct definition is the ISO standard. That standard is careful to avoid specifying how ISO is implemented. It only addresses aspects of mapping the exposure to image lightness in the resulting image.

I think it is good start to explain to beginners that light is comprised of photons, and "exposure" is determined by the photons reaching the sensor, and I think it's useful to think of the pixels as roughly counting photons. As a general rule (and there are exceptions), the pixels seeing more photons report higher numbers.

I think it's also a fair overview to suggest that the ISO setting gives a context for interpreting those numbers. Clearly, ISO is not the only factor, as the pixel size, bayer pattern filter, and other camera specifics also play important roles.

Obviously, the above is a gross simplification. For instance, it ignores Bayer Pattern color filters which block many photons from reaching the sensor. However, my goal was not to teach someone the details of how cameras work, nor to teach them every nuance of photography. It was merely to teach the concept of how ISO influences the process that maps exposure on the sensor to image lightness in a camera produced JPEG.

Actually, one does. ISO is like the "stick" which is popular around the world, not so much in the US. Even auto transmission cars often have a manual override.

IMO, all is lost once car analogies come to the fore.

That doesn't help people shooting raw. Are you suggesting that beginners don't shoot raw? That would certainly simplify the explanation, but I thought we hadn't eliminated raw.

My fault, sorry.... ;-)

Isn't the initial answer for beginners:

ISO relates shutter speed, f-number and subject illumination to the lightness of the resulting image.

Use the slowest shutter speed and widest aperture (lowest f-number) consistent with desired motion blur (subject movement and camera shake) and desired depth of field, without blowing highlights you want to preserve. Use auto ISO. Use software to adjust how light or dark the image appears, as appropriate.

I usually think of this for raw, but I suppose it applies to jpg too.

Does an actual beginner need more?

I like that. "ISO" is like the gear in a car. With different gears, the same engine RPM translates to different speeds. However, while I have a manual transmission car, there are a lot of people today who are not familiar with them, and therefore may not find that analogy helpful.

So, if I am in a gear that is too low, am I wasting energy/photons?
I have never seen any car analogy that works for photography. However, I understand that many would like to talk about cars. Can we add a car forum to DPRevived?

P.S.: I love cars.

But then if you are shooting in an auto ISO mode, you do need to know what ISO is in the first place?

A big issue is that the ISO standard does not apply to raw files. Therefore it is much easier to introduce the concept with the camera set to shooting JPEG (a scenario envisioned by the standard).

Once you are shooting raw, and manually processing the data, the ISO setting on the camera is no longer the ISO setting used by the process. Remember, the ISO standard is about the mapping of inputs to outputs. How this is accomplished is a "black box" to the standard. The raw file is an intermediate step inside that black box. Therefore it is not something the standard addresses. Any affects ISO has on the raw data is an implementation detail. that varies from camera to camera. As has been mentioned, there are even cameras where changing the ISO setting does not alter the raw data.

I think it's best to introduce ISO in the context of camera produced JPEGs. Once the concept is understood in that domain, the explanation can be expanded to other domains (such as shoot raw).

Once you expand to raw files, the implementation details become more important. The ISO of the "black box" is influenced both by the ISO setting of the camera, and some of the image processing settings of the raw processor. Some of the processing is being done by hardware/firmware in the camera, and some is being done by the raw processing software. Determining the ISO rating of the result isn't always trivial.

At a rough approximation, we can start an explanation of ISO and raw with the exercise of shooting everything at base ISO (often ISO 100). While the camera produced JPEG will often be far too dark, the beginner can see that they can control image lightness by adjusting various parameters of the raw processing software. In essence these parameters determine the ISO of the raw to JPEG conversion. I am not suggesting that locking the camera at base ISO and shooting raw is a preferred workflow. I am suggesting that it is a useful exercise for introducing beginners to the concepts of how ISO relates to raw shooting. Once they understand this, then you move on to more complicated situations, like shooting in raw with Auto-ISO.

When shooting with Auto-ISO, it is still helpful to understand the concept of ISO. By paying attention to the ISO selected by the camera, you can get an idea of the level of exposure on the sensor, and this helps you predict how noisy the image will be.

Photography often requires a balancing act between sufficient depth of field, minimizing motion blur, and minimizing noise. When deciding on the best compromise, it's helpful to know what ISO the camera thinks is appropriate given the aperture, shutter and subject lighting.

I think that's a reasonable framework. I am currently working on a tutorial on exposure for mid-level photographers shooting raw, and I'm going to include a short discussion on ISO settings, though it does not affect exposure. I'm going to play down the importance of ISO settings once you get above base ISO. I think too many raw shooters think ISO setting is as important as exposure.

I don't find that last sentence true for me, unless I can control the lighting intensity -- and these days I usually can.

Yes. I find that I use different strategies when I a in situations where I am "light limited" than when I am not.

By "light limited" I mean that I can not increase subject illumination to the point where I can achieve the exposure that I want, at the shutter speed I want with the depth of field that I want.

When I am shooting in my studio, I generally have enough light for a base ISO exposure. I set my aperture for the desired depth of field, my shutter is set to the camera's sync speed, and I vary the overall intensity of the lights to give me my desired base ISO exposure. One way to do this is to set the camera to Auto-ISO, and vary the lights until Auto-ISO chooses the base ISO.

In situations where I do not have the ability to increase the lighting, I need to find a reasonable balance of depth of field, motion blur and image noise. If the camera is set to Auto-ISO, the chosen setting gives me feedback as to the expected exposure, and that is useful in estimating image noise.

My experience is that there is no single workflow that works best in all situations.