What elements define a good abstract macro photo?
So much of what I do is subjective, but I do think that relying on the elements of design (defined here) and composition which have been hallmarks of abstract art for the past 100+ years is key to defining what makes a good Macro Expressionist abstract photo.
When I begin a photography session I make sure that the light is optimal to illuminate my subject. Back lighting from the sun rising or setting is an excellent tool for building transparencies in the frame. Because I shoot a lot of flowers and plants, sunlight is key for adding drama and accentuating colors.
I love the atmosphere light creates when it peeks out from behind a stem or flower petal and brings contrast to the image or the background is dark and gives the image atmosphere and depth.
Space is another element that makes abstract macro photos have a larger than life feeling. The key is to make sure what seems to be the focal point, usually the main object I am shooting, is offset and the elements around it or behind it have a definite color or light value difference so that they are heavier and lighter looking spaces in the image.
Line leads the eyes through the frame. Line can be virtual or abstract. It can be implied with lights and darks overlapping or colors meeting and creating edges.
Overall, using the core elements of color, line, light, space and value combined with intangible qualities such as atmosphere, mood and mystery, a solid abstract macro photo can be created.