Originally Posted by Cesaraugusta
You do compose for the frame you happen to have.
Composition is nothing but arranging things inside a frame, and you can do that equally well - differently, but equally well - throwing the same things around in different frames.
You do run into things that will not sit good, no matter what you try, and then you compose to an imagined frame, and cut away the parts that are not part of the composition later.
But you do compose, square, oblong in many different aspect ratios, and round even.