Jimmy Pop wrote:

I have been using a "prosumer" camera and was looking into upgrading to the
20D. What is the reasoning behind the 3:2 aspect ratio?

It is the same as 35mm film, and it is a shape many of us rather like. I
hate 4:3 with the white-hot heat of a thousand suns.

I did most of my printing before on A4 Letter paper (8.5 x 11) which fit
the 4:3 aspect ration much nicer. What is the target print size for the
3:2 aspect ration? It seems to fit the 4x6 paper size nicely, but doesn't
seem to line up as well with the larger prints (8x10, 8.5x11).

There is no "target print size" for any format, because all of those sizes
you think of as standard for printing are different shapes. What fits a
4x6 won't fit a 5x7 or an 8x10; those paper sizes are arbitrary and have
become standard photo print sizes for no good reason at all. Especially
in this day and age, there is very little reason to stick to them.

The 3:2 ratio prints full-bleed on 8x12, for example, and any decent
printing company will offer that size.

5x7 paper is very close to a 1.414:1 ratio; 8x10 is of course 4x5. Both
of those shapes, while common aspect ratios for both photography and other
art forms (the former is used in graphic arts, the latter in large format
photography), are not the shape of virtually any digital camera sensor.
If you use 8x10 paper in particular, you will need to leave large borders
on two sides of the print (larger than the other two sides), or you'll have
to crop, neither of which you probably want to do. Or, change your paper
size either by trimming or by using a more appropriate size in the first
place.

For my own prints, I rarely print full-bleed (borderless) since I prefer
a small border; I stay away from 8x10 paper because it's not useful; I
live with the slight border size differences on 5x7; and I often actually
compose in camera with a 1.414 ratio in mind for vertical compositions
anyway, which fits nicely on 5x7, which is the size I usually get most
everyday prints in.

--
Jeremy |