I painted this painting as a demonstration for my class in Rockland, Maine and I think the demonstration was effective in explaining how to get the basic values and shapes established within about an hour. This amount of time should give you pretty consistent light unless you are painting right around noon and the sun changes from one side to the other. I try to give myself about an hour per painting and then finish a few details back in the studio. Although I don’t think this really qualifies as a true plein aire painting I am not all that concerned about definitions. My work in the studio usually involves making sure the value planes are right, that the shapes are interesting and that I have the light stated correctly, if I have to do more than that I didn’t work with enough focus in the field.
finished painting “Summer Returns”
field version 
In the final version I put some reflections in the water in front of the rocks which softened the shape. I darkened the water to get a better contrast for the boats, which I added light to, and the rocks, which I also added light and highlight to. I added some light to the weeds with a palette knife and lightened the grass a value or two. I also toned the distant islands down by graying them I think they were too blue in the original. I think the changes help the painting although the field painting was nice it just didn’t work for me as a finished piece.