Hi @OldFrog ! Sorry, I just saw this! Thank you for replying. 70mm! That’s a lot wider than I thought. I recently purchased an old Keystone viewer from eBay and took measurements. It appears that these had an IPD of about 63mm. I noticed that the lenses faced a few degrees inwards as well. Also curiously, the center level of the lenses were 18mm lower than the center level of the images on a standard 3.5" x 7" card. My guess is that it forces the user to pitch the viewer down 7.5˚ allowing more light to hit the card - I imagine 100 years ago not every home had electrical lights. It also perhaps avoids possible shadow casting on the image plate. Is this correct in your experience? In my design I plan to have the lens center aligned with the image center since that is the case with VR content, but please let me know if there is a specific reason why I should stick with the traditional alignment.
Roger on the camera lens separation . That’s a big concern off of my mind. Speaking of camera lens separation, the stereo shot of the full moon you mention - I had a bunch of stereo cards (all from Keystone View Company) that came with the viewer and one of them was of the moon. Is this the one you mean?
I’m surprised to see I wrote that about 70mm. I think I got distracted during my draft. I meant to say “I ‘own’ viewers with the lens centers spaced from as little as 55mm (a Keystone eye exercise set) and as great as 70mm (a 3D dental x-ray viewer).” The jig I made for making my lens boards had the lens centers at 55mm patterned after the “PerfectScope”. The dental x-ray viewer most certainly would have only been used by an adult so there was no need to make accommodations for younger viewers (pure speculation).
Although pre-made lens sets are available in both glass (two pieces) and plastic (one piece - preset spacing) I chose to cut my lenses from magnifying glass lenses. That was a lot of extra work but I got the lenses really cheap. Whatever money I saved, I lost on what it cost me to set up small jeweler’s table saw and the several jigs I had to make. Though currently ‘out of stock’, the glass lenses are available through Berezin Stereo Photography Products; https://www.berezin.com/3d/lens.htm rather pricy at $30 a pair. No wonder I made my own. Right now I’m not finding the plastic lenses online.
Regarding the lenses being lower than the image center on the cards, I don’t think there was any functional reason for that arrangement. Maybe just to make the viewers less bulky, I don’t know. It’s still easy to see the entire image(s) on the cards without perfect lens to card up/down centering.
Your stereo card of the moon is a bit different than the one in my collection. Mine is a ‘full’ moon while yours appears to be about a ‘3/4’ moon. Still, a great stereo card.
Attached is an image of one of my scopes which I never finished. This one is made using Australian Lacewood and lenses I cut myself. I never got into trying to bend thin plywood for the hood. I just cut mine from fairly stiff leather. That was another jig I had to make. I embossed some of those with dies I had made, which just added to the cost. Just imagine how easy it will be to make the hood with the Glowforge, and how fancy a pattern you can add. I just might finish that lacewood viewer after all.
Hi Stephen - thanks again for all of your insight. The link to the lenses was particularly enlightening. I now see that the lenses are not pointed inwards but in fact, a much larger diameter Plano-convex lens but cut so that only one half (or perhaps a quarter) is used, making the object side seem to yaw inwards. This is quite ingenious since it allows for a greater focusing distance without having a giant viewing lens, making it more economical and lighter. $30 seems a little much, but probably much cheaper than trying to make them myself since I’ve no plans to mass produce them any time soon. Anyway, a great insight and most helpful link!
I’ve seen videos where people make stereoscopes with +3 diopter reading glasses. I haven’t fully rigged it up, but after a quick mock up it doesn’t seem to work. I was doubtful in the first place but I was vexed that this was being shopped around as a solution.
Beautiful scope! I can see how a can really help speed up the process. I’ve done quite a bit of kerf bending with mdf for my laser cut ukuleles with great success but it hasn’t worked very well for hardwoods or plywood. It just snaps. Your leather idea not only sounds workable but I am sure it is going to be quite handsome when complete. I look forward to seeing it!
can really help speed up the process. I’ve done quite a bit of kerf bending with mdf for my laser cut ukuleles with great success but it hasn’t worked very well for hardwoods or plywood. It just snaps. Your leather idea not only sounds workable but I am sure it is going to be quite handsome when complete. I look forward to seeing it!