Checking value

I managed to get out to paint today, and took some "big" panels, 11x14 in. I went back to Helen Putnam Regional Park in Sonoma Co, looking for patterns of live oak and golden non-native grasses. I've been struck recently how different the sky looks now that the weather is hot and I wanted to check the relative values of the hills and the sky this afternoon. I had a small brain wave and pulled out my digital camera. By selecting black and white mode, I was able to estimate relative value just by looking at the screen. This particular value contrast has given me trouble before, because the hills are so yellow and the sky is so very blue. (There's another post here) By using my camera, I was able to confirm that the sky was darker than the sun-drenched hill.