« The Four Stages of Seeing | Main | The Beauty of Imperfection »

July 20, 2009


I usually change the ISO when I want more light in my photo. I am really curious to know what's the best choice.

I'd adjust the exposure compensation +1 stop. If the meter is underexposing, I would imagine that it would still underexpose the scene at the next higher ISO.

Honestly, what I would do is to slow down the shutter speed or open up the f/stop, because I just don't think about using exposure compensation. Which one I would do depends on the shot.

If I could get away with it, the first thing I'd reduce is the shutter speed. However, if the shutter speed would be low enough to introduce offensive camera shake, I would open it up a stop. Barring that, I'd raise the ISO.

Shutter speed is first because I tend to like keeping my lenses at their sweet spot. ISO is last because my D80 becomes offensively noisy once it hits 400 ISO.

Good question and one that didn't enter my mind before the digital era. As a general rule, I set my ISO at the beginning of a shoot and generally only change it when the lighting changes. For changes to individual shots, I use Exposure Compensation primarily because it prevents me from forgetting to change the ISO back.

For me, I generally set my ISO to the available light and solve shot-to-shot variation via EC.

You pose a great question and one that I believe is solved typically based on how someone learned to shoot. For film people, unlearning years of shooting with a given film speed is tough to overcome. Younger people aren't hindered by this thinking and, I would propose, might not be psychologically "set" shot to shot.

Using Program or Aperture mode I would dial 1 stop overexposure. If in Manual mode I would dial 1 stop slower speed or bigger aperture.

As with most situations: it depends.

First of all, "Auto Exposure Compensation" (AEC) only means anything if you're using a mode in which "auto exposure" is used (such as Av, Tv, P). If you're shooting in "Manual", then it doesn't even apply. (For the sake of simplicity, I will also not discuss the use of flash.)

I rarely shoot sports or other subjects in which the shutter speed is a critical factor, so what I really care about is the depth of field. This means that I barely ever touch the P or Tv modes, as I would never want to leave the depth-of-field as a surprise.

So, apart from Manual mode (which I use most of the time), that leaves me with Av for the times when the light is changing rapidly/unpredictably. I set the aperture I want, let the camera decide of an appropriate shutter speed, and hope for the best. In Av mode, compensation changes the shutter speed: to get 1 stop more, it would expose twice as long. I don't care what shutter speed is used, so long as the camera is hand-holdable and the subject is reasonably frozen.

Only as a last resort, when I cannot go slower, will I raise the ISO, as raising the ISO degrades image quality. Of course, I prefer to have some noise than to have a blurry picture, but I will always favor the lowest ISO possible.

"I'd adjust the exposure compensation +1 stop. If the meter is underexposing, I would imagine that it would still underexpose the scene at the next higher ISO."

Congratulations, Tom! You zeroed in on exactly what I was implying with my question. If your camera is set to one of the auto modes and is underexposing, then setting the meter to a higher ISO will simply cause the same amount of underexposure but at a higher ISO. The solution would be to increase the auto exposure compensation by one stop.

If, on the other hand, you were shooting with your camera set manually, you could either increase the aperture, the shutter speed or the ISO by one stop.

Now, for those of you who really want to test your exposure chops, how would you answer the same question if you were using a portable flash unit?

@ Gordon: time to open the lens a stop.

With the flash it gets more complicated, because it depends how you use it.

Is the flash the *only* source of light? Or is it the main source of light, with the ambient light used as well? Or is it merely a fill light, with the ambient light as the main light?

Unless the flash is the only source of light, you'd want to keep a certain ratio between the flash and the ambient light. Therefore, some parameters cannot be changed alone without breaking the ratio.

For example, changing the shutter speed won't have any effect on the flash light (let's not dwelve into the topics of x-sync/high speed sync), and changing the flash power won't have any effect on the ambient light. On the other hand, changing the aperture or the ISO will.

Depending on the situation, unless you're working completely manually, you'd have to use either (or both) of the Auto Exposure Compensation (AEC) and Flash Exposure Compensation (FEC).

Open up the aperture 1 stop (or more) or if shooting shutter priority use the exposure compensation to open the aperture.

"I always live in the matrix" (McNally dixit). Hence, I keep on playing with AEC up and down from photo to photo. I know what I want from a particular photo and how to get it right using only these controls. I only raise the ISO in unmanageable conditions (below hand-holdable limits). If I have to use a particular shutter/aperture, sure I have to crank ISO up, but it goes last in the equation. I must also say that auto-ISO helps a lot, as my AEC+1 can increase my shutter speed and, in a second instance, increase the ISO.
Good food for thought!


You're right. With flash it can get a lot more complicated--mostly because you're often dealing with two exposures: the ambient light exposure and the flash exposure. The trick is to determine which one is under or over-exposed. It could be both. Suffice it to say that you have to be on top of your game to get consistently accurate, well-balanced flash exposures and I have no doubt that you are.

The interesting about the question is, that at the first sight I could not determine what the question is.
If one works on film, the only possible solution is to use the exposure compensation. Even if I change to digital, I could not even see the changing of the ISO value, or the opening up one stop as a possibility.
I also think those who chose the B option would not do this in a real photografic situation.

The comments to this entry are closed.

Tip Jar

Thank you!

Tip Jar