Originally Posted by
JMO
To the OP, another thing to keep in mind is that if you are in the field and using a spot meter to determine your exposure, you can meter the scene through the actual colored filter, so you can determine what effect the filter will have on your exposure in different parts of the composition. When I do this, I have found that the mfr's recommended filter factors are usually a bit too strong, so if you follow them you'll often be overexposing somewhat. But you're in control, and with experience and all of the good advice above, you'll become more confident.