What is ISO?

The other day a buddy of mine asked me about iso. I don't want to go too in depth about iso considering there are a bunch of resources online, but here are a few key things to know.

1) Sensitivity - ISO is the sensitivity of your film or your digital sensor. It's easy to think about...the higher the ISO # the more sensitive the sensor is to light (ie ISO 100 is less sensitive than ISO 1600).

So why would I want to change ISO?

2)Lighting conditions - During a bright sunny day there will be a lot of light hitting your sensor. In this case you can use a lower ISO because there is lots of light. If you were to go inside though, you don't have as much ambient light. Therefore you would want your sensor to be more sensitive to light and you would increase your ISO.

3)Noise - The problem with ISO is that as you increase your ISO the more visible noise you will get in your pictures. Easy rule; Higher ISO=More Noise. Noise appears as little dots on your pics. Not cool! This is especially true with point n' shoots where you will be limited to using lower ISO to get clean images. Here are some examples (thank you www.cameralabs.com for these images):In this example the left pic was taken with a point n' shoot (Canon G10) and an SLR (Canon 450D) on the right. Even at ISO 100 you can notice that the 450D pic is cleaner, with less dots than the G10.

In this example the pics were now taken at ISO 400. On the left, the point and shoot is starting to show a lot of visible noise (click the image to see higher res). The SLR on the right is still clean with little additional noise.
...and finally ISO 1600. The point and shoot on the left is stugglin'. Many cameras will try to fight noise with software, but this noise reduction "smears" the image making it less sharp. The SLR on the right is now showing some noise, but the detail is still there and usable.

NOTE: the G10 is the top of the line point and shoot from Canon going for ~$500!!! Lower end cameras will probably display even greater noise at high ISOs. The 450D is the bottom of line DSLR. It goes for ~$560...check out B and H for camera prices. You can even find used equipment there. Here's a good deal on a base DSLR (Canon XTi). Only $329 used!!!

I don't like noise!!! If you have a point and shoot you're probably getting a lot of noisy pics...well buy a digital SLR...they're cheap now!! These cameras allow you to use higher ISOs without nearly as much visible noise as point n' shoots. If you really like your point and shoot, and don't want to make the switch to an SLR, then here's your rule of thumb:

Use the lowest ISO possible for the conditions you're shooting in.

This is the key rule whether or not you have a point and shoot to get the cleanest images possible. Some newer cameras now even have an "Auto ISO" setting that does this for you. The camera senses how much light there is in the picture and then automatically chooses the lowest ISO possible to accomplish the best exposure. Use it if you have it!

Here are some more resources on ISO if you really want to learn all the intricacies:

http://www.photoxels.com/tutorial_iso.html

http://www.cameratown.com/guides/iso.cfm