Since this is more or less repeating my last post, I thought I would show my little homemade view finder tool.
I made this years ago, as you can see by the smudges and dried paint, from a 5x7 gray mat you can purchase for framing photos. I cut the corners, then marked off the interior edges, starting at the corners going out, every half inch. I can view my set up through my adjustable opening and determine exactly what size canvas will make the best composition. Once that is decided, I paperclip the corners and continue to use it to help locate the major shapes during the drawing phase. The mid-toned gray can be used to judge values as well.
Now back to fun with flower!