Updated 2015/4/12, Major revision
Got Google's Cardboard, it's an inexpensive VR (virtual reality) viewer for smartphone displays. Bought mine from "Unofficial Cardboard" with the idea of seeing how my 3D stereoscopic photos look on my phone with the Cardboard viewer compared to my 3D tablet (Inferno/Gadmei INF2890).
None of the Android stereo viewing or VR apps I tried worked as I would like with my photos. The cardboard lenses limit the viewing area on the phone since the headset is meant to move around to change the display with VR apps. I don't want to have to move my head around with the viewer just to see a stereo 3D slideshow. Of course for panoramic photos that is a great feature, but my photos are not panoramas. With many photo apps, it was cumbersome to get my photos to be the right size for viewing in Cardboard. So instead I used an easy method to view my 3D photos in Cardboard without VR apps.
For my Sony Xperia Z1S phone (1920 W x 1080 H screen) I used StereoPhotoMaker to resize side_by_side stereo photos to 1920x540 pixels (with black borders if necessary to match the display width of 1920 specifically for the Z1S). Each eye view has an aspect ratio of 16x9. In the Cardboard viewer I look at photos in full screen mode with an app like Full Screen Pic. Full screen viewing mode is a requirement. The result looked good with Cardboard, and actually much better than my 3D tablet. However I can see the pixels of the photos due to lens magnification.
With more experimentation I improved the viewing experience using side_by_side photos resize to 1920x720 pixels. Each eye view has an aspect ratio of 4x3. This turned out to be a better viewing experience with cardboard. The cardboard lenses prevent seeing the entire photo (on the edges), but with more pixels the images look better. Finally after yet more experimentation, I cropped the photo to 8x9 aspect ratio to get the best results. On the 1920x1080 phone this produced full screen images. Looks great if you can use this aspect ratio for your photo. Finally I used different lenses that do not limit my field of view in a homemade cardboard viewer. I may discuss this topic in another post.
Placing the main subject in the center of the photo helped too. This may detract from the art of composing photo subjects as would be done in 2D photos (such as with rule of Thirds).
I also experienced some eyestrain discomfort, but this may be due to how near my eyes are to the lenses in the cardboard frame, because when I back away the image is sharper.
Full Screen Pic has a slideshow mode that works well because it does not use or can turn off annoying transitions or zooms and it works in full screen.
