*IMO, aspect ratios are the providence of post programs. Some images are seen in the mind's eye as one ratio, some as another ... programs like Lightroom ect., allow any ratio you wish. Sometimes the square is most pleasing, other times the Golden mean works best, and yet others sing as panoramas.*
Thanks, Marc — what you say does make sense, especially in regard to freeing the mind by hanging loose to the options dictated by the equipment. I'm just used to using whatever format is at my disposal, putting the best frame I can around the scene and not cropping much later, if at all. I also like to get so used to my equipment that I can frame in my minds eye even before the camera gets into position for the capture. Since I do that better at that with a familiar prime and 4 x 3 than with the same prime and 3 x 2, I'd prefer, if possible, to choose my default frame before the fact rather than afterward. Hence the thought about the Golden Ratio, which has always fascinated me, but I'll experiment with floating a post processing frame around some of my existing images and see where it leads me.
*Another option would be to order another type "G" Sony screen, and using a X-acto type knife, a straight edge and india ink, craft your own custom grids.*
Thanks to you, too, Graham — I actually hadn't thought of that and will look into it.
Cheers,
Irenaeus