Photography Basics - ISO Setting

[Sylvanite]

My goal in this series of discussions is to explain the underlying concepts of photography so you'll understand when, why, and how to change your camera settings. I don't want to simply describe digital camera controls. However, I'm about to do just that. A member asked for a tutorial on "ISO Setting", so here it is.

I've characterized "ISO Setting" previously as controlling the digital camera sensor's sensitivity to light, but it's really more like amplification (or "gain" to the purists). Here's an analogy. Imagine you like to listen to two radio stations. One of them is nearby and you receive a clear, strong signal. The other one is distant and the signal is faint. In order to hear both at the same volume, you'll need to boost the weak signal more than the good one. When you amplify it, you introduce noise and distortion.

The same thing goes for a digital camera. Pretend that you take two pictures - one with ample light (exposure) and one with less. You can amplify the signal coming off the camera sensor so that the second image is equally as bright as the first, but you're going to introduce noise and distortion. That's what the ISO setting does. Just how much noise you get depends on the amount of amplification and the quality of the sensor.

Digital camera sensors are getting better and better. Some suffer very little image degradation, but it's still there. Professional quality camera bodies can handle high values, but many consumer cameras visibly lose image quality at ISO 400 or less. For the best photographs, you'll generally want to use the lowest ISO setting you can. For most digital cameras, that's ISO 100. If you have trouble getting a good exposure at ISO 100, you should first try to add more light. If you can, use a tripod and a slow shutter speed. Increase the ISO setting only as a last resort, and do so sparingly.

I hope that helps,
Eric

 

[edstreet]

When you double the ISO speed you double the sensitivity.

i.e. changing from ISO 100/21° to ISO 200/21° is twice as fast.

--

Larger grains (Silver halide) give film greater sensitivity to light. The larger the grain is the easier it is to see them in exposed images.

 

[Sylvanite]

Here are a couple of photos that illustrate the noise that using a high ISO value can introduce. I have friends in the fiberglass business who asked me to photograph one of their projects. It isn't a pen - instead it's a circular dormer window frame. They took me to the development where they were installed just as the sun was setting. I had very little time to set up and let the camera choose the exposure. This is the result:

The camera used an ISO setting of 3200. I knew even before taking the photo that I wouldn't be happy with the result. Looking at the reflection of the sky in the glass, or at the underside of the fiberglass window frame, you can easily see the digital noise (a.k.a. "pixelization").

So, I went back another day (when the sun was still up) and tried again, this time manually setting an ISO value of 100. This is the second version:

There's very little noise in this photo. The reflection in the window is evenly toned, and the fiberglass surface colors look smooth.

These aren't pen photos, but the principle is the same. You'll get better pictures with less noise if you stick to low ISO values.

Eric

 

[ashaw]

Eric you did a great job at the MAPG