En plein air is French for in the open air. Simply put, plein air painting is painting outside from life. If an artist desires to become a landscape painter, then learning to paint the landscape from life plays a crucial role in seeing the landscape for what it is. Only then, does one see all the subtle and reflective colors in a shadow. And only then do you realize that white is never white but a light value of blue, gold or crimson.
Photography lies. It knocks out the highlights and gives you black shadows. Generally the values in a photo will only be somewhat accurate in the area of focus - either sky or land but not both. You can compensate for this by taking many photos of the same view and focusing on land in some, then sky in others. If I don't have the luxury of painting on location, I will easily take 20 photos of the same spot but different compositions. I also carry a sketch book for doing quick value sketches. But painting on location is always preferred.
I've had the opportunity to judge several art shows in the past year and I can almost always tell who is painting from life and who is painting from photos. You can see it in their shadows. Shadows are not black, yet I see so many people paint them this way.
Really understanding a particular type of landscape takes a little while. I've been driving through and painting the Flint Hills for a long time so it's second nature. There are other parts of the country that I'm becoming familiar with, such as the dramatic Rocky Mountain landscapes of Colorado and Wyoming, or the dry, crisp landscapes of New Mexico and Arizona. Because I don't live in these climates, it usually takes 2-3 days for plein air painting to feel comfortable again. That's why when I take a painting trip it's for at least 7 days or longer. By the seventh day I'm usually feeling pretty good about my results.
Artists have different view points on plein air painting. Some believe it's the end all be all. They create most of their work outside and believe the piece should be finished on location. Others start their work outside, then bring it indoors to their studio, usually along with photography or sketches, and finish the work indoors. Still others paint what they consider to be studies outdoors. Smaller work, usually 6x8 to 12x16, painted entirely on location but not necessarily considered a polished painting. The main objective of a study is to provide enough information about composition, value and color so an artist can go back to the studio and create a larger studio piece based on the study. I approach plein air painting from this angle. When painting on location, I'm not concerned with creating a polished work, just getting the information. I also take photos and many times sketch. All of this comes back to the studio with me. Then I ask the questions "Does this subject interest me?" "Do I want to see more, explore it further?" or "Is this as far as I want to take it?" If the answers to the first questions is yes, then the study is used to create a larger studio piece. If the answer is no, then the study either wasn't interesting, or it said everything it needed to and there's no need to explore this subject further.