There are straight magnifiers too but again these only magnify the center portion.
Basically vfs are divided between small or large magnification to accomodate people who wear eyeglasses or those who don't. For instance, the EOS1V has a magnification of .72 compared to the Pentax MX of .97. The near lifesize view of the MX is significant but of course not great for folks who wear glasses.
The Pentax LX has interchangeable viewfinders and screens that can offer huge bright views.