Pine, 1892, by Ivan Shishkin
It's an age-old question: Should you as a plein-air painter try to capture exactly what you see, or should you deliberately make changes?
Ivan Shishkin said: "The main thing for a landscape painter is a diligent study of nature. Because of this, the picture from life must be without imagination." John Ruskin said that the student should: “Go to Nature in all singleness of heart, and walk with her laboriously and trustingly, having no other thought but how best to penetrate her meaning, rejecting nothing, selecting nothing, and scorning nothing.”
I don't think Shishkin is really dumping on imagination. Instead of the word "imagination," we might substitute "conventionalism" or "idealization."
I sympathize with what Shishkin and Ruskin are advocating. There is a real joy and challenge for trying to capture exactly what's in front of you without changing or editing or "improving" it. Of course attempting to copy a scene from nature in all its color and detail is not really possible. You have to make choices and simplify something, because you can't capture it all.
Back in the studio, armed with these studies, the artist can assemble the raw material of plein-air studies to create a virtual world of imagination.
I like having a lot of different conceptual approaches ready, like arrows in a quiver, when I head out. Sometimes when I'm on location I want to hold a mirror to nature. But other times I like to exaggerate, elaborate, or invent a fantastical scene while looking at nature.