I can free view the old stereo cards in parallel mode with no problem and the depth is normal and not inverted as happens if I use the cross-eyed mode for them. The parallel mode does give a larger image than the cross-eyed mode but is a little harder to fuse the images as another has pointed out.  It does require slight divergence of the eyes, but I've known a number of people over the years who can do it without much effort or eye strain. If I recall correctly, I learned by focusing on something in the distance and then shifting my attention to the card and a single image came into focus. You shouldn't need to strain your eyes to do it -  in fact just the opposite, relax them. For larger images the parallel mode won't work and I have to use the cross-eyed method.

Steve

I have been able to free view in both parallel and cross-view modes for many years and have collected stereo views and made my own , both cards and slides. With practice most people can achieve cross-view viewing and a lesser number - parallel viewing. I've always enjoyed viewing in stereo and am pleased that the interest in this form has increased recently.