Using graduated filters with a light meter
Graduated filters are a must for landscape photography, they allow you to control the dynamic range in your shot without resorting to digital manipulation and HDR techniques, which I find often produces results that look a little like film CGI. However, for anyone using a handheld light meter to measure your scene you may be wondering how to get accurate results; you've got your shot composed nicely and you've added on a 2 stop grad to darken down the sky so the clouds look moody, but how can you account for the effect of the grad with your spot meter?
A better way to look at this is to use your meter to record the dynamic range of the scene, then use the information to decide how much of a grad (if any) you need to use and also where to place it.
The big advantage of a hand held spot meter is that it lets you record multiple readings and then see them all on a display, this gives you an overall picture of the light levels in your scene.
Take a look at the meter above. I have taken 3 readings to show me my shadows, mid-tones and highlights. The meter shows my that my shadows fall about 1.5 stops lower than my mid-tones, but my highlights are over 4 stops above my mid-tones. If I expose my shot correctly for the mid-tones, I'm going to blow my highlights. The small arrows just above the numbers show me how much latitude I have to play with before either losing detail completely in my shadows, or blowing highlights and whiting out parts of my shot.
I have a little room to play with here, if I drop my exposure by 1 f-stop my shadows should still expose ok without losing much detail and my highlights move slightly closer to being inside the arrows, but still not enough to prevent them being blown. A better option is to use a grad filter, and by looking at the meter reading I can see that I want to use a 2 stop grad. This will bring my highlights from being just over 4 stops above my mid-tones, to being just over 2 stops above my midtones.
By placing the grad just at the horizon I've also dropped the shadows and darkened down the land in the distance somewhat. Now the whole scene falls within the latitude of my camera without losing shadows or highlights.
This is the best way I have found to use a spot meter with grads, if you use a different method I would love to hear about it.