closeup optics question: stereogram viewer
I would like to make a simple ViewMaster, but for 6x7 film instead of those little postage-stamps on a wheel. I figure this thing will be to projection as headphones are to good speakers In other words, I'm trying to build viewfinder optics; something to make a view-filling image from a frame.
What sort of closeup lens do I need so that the user's eye can focus on the chrome while filling their vision? How many dioptres do I need for typical vision? Would it be reasonable to use a pair of closeup dioptre/filters intended for use on camera objective lenses and can I assume they'll have good enough FOV on an eyeball and sharpness across the frame? Do I need any optics other than a closeup filter?
No I'm not going to use two RB67 prisms! I want this to be usable by people other than weightlifters, not to mention people with an inter-pupillary distance smaller than an elephant.
I really have no answers, but had recently gotten into stereo photography. I bought a Realist 45 on ebay, and it looks as if it only had a few rolls of film through it. Still waiting on a real Realist in my price range (hope to get a Custom).
You've probably searched the web and found sites like this:
So I won't post a bunch of links unless you want some.
Anyway, I've seen Holga viewers and masks on ebay, but they'd likely be too small. I'm sure they are not great, but might make a good starting point when building your own (I often modify new toys to suit my purposes).
Considering you will be using 6x7 transparencies, perhaps you could adapt an Holmes style viewer, or the Owl Viewer designed by Brian May. You images won't be that much different in size than a "standard" stereo card, so I'd imagine the optics and distances would be a good starting point. (I'm guessing each image will be 6x7, not the pair combined.)
Are you going to make reels like a giant Viewmaster?
Yeah, I've seen a few websites discussing stereography and there are definitely commercially-available stereogram viewers that seem aimed mostly at prints and digital (on a monitor) images as they speak of image sizes of 100mm to 300mm. The Owl does look quite suitable in its dimensions but I'm not convinced by cheap plastic lenses. Does anyone know how many dioptres they are?
I want more magnification than that. Yes, each image is 6x7 - I've been shooting with an RZ and a lateral macro rail.
sounds to me like you are reinventing the wheel -- stereo views on cards were about the size you mention and viewers for those are pretty easy to find. The lenses for a Holmes-type stereoscope -- the thing your grandmother had in the parlor -- are still commercially available, I believe -- Get yourself a pair of those and you'll be set.
http://www.stereoworld.org/stereoWorld.php is the web site for the National Stereoscopic Association -- many many helpful folks there.
I shoot stereo with 120-size cameras -- a russian Sputnik or a French Richard Verascope -- contact print the negatives and mount the views on cardboard for viewing.
I dug through links I had from about six months ago, but all I could find was a company selling lenses for Holmes-style viewers:
They state it is about 200mm in focal length, which as best I can figure is somewhere around 5 dioptre. However, never trust me with numbers - math and I are not on speaking terms!
Dr T's ebay store mostly has plastic-lens MF viewers.
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Thanks; +5 dioptres looks like a good starting-point then. The Berezin ones are probably fine but shipping to AU is $$ so I'll do a little more hunting.
I guess you're going for realism, so I'd say the place to start is... same focal length as used to make the photos - presumably about 90mm for a "normal" focal length, roughly 11 diopters. If you want to test out the concept, just use the original lens to inspect a contact print.
There was some discussion of "proper viewing distance" of prints several months ago, in this thread:
In my post #83 I attached a sketch from an old "how to draw" book, demonstrating an idea of how "proper viewing distance" works with different image sizes.
In other words, my suggestion is to NOT approach this as an attempt to fill the field of view, but rather to go for the "proper viewing distance," then use optics allowing the eye to focus at this distance.
I don't know how to get both eyes to work together for this, so perhaps some trial and error. If you don't already have a set or two of closeup lenses, perhaps you have some low-end enlarger lenses to play with.
Keep in mind what I said about checking my math, seriously.
Also, I'd think different strength lenses would give you different distance to the chromes, which would help keep the size (length) down (see Mr. Bill's point about distance).
You could do a mock-up with cheap parts to find what you need, then search for good materials.
Tape something together made of cardboard, using lenses from cheap drugstore reading glasses (in various magnifications), etc. just to get a feel for what may work best for you.
You could even use a pie tin for the reel
So Berezin also sells a "pinsharp" device for 50x50mm slide mounts, which has a 47mm focal length or +21 dioptres. It's intended for much smaller images than the Owl and Holmes though, which would explain the difference in focal length.
I don't have any closeup dioptres or I'd just try them. I do have some enlarger lenses (of focal lengths similar to what I shoot with) though so I'll start with those to see how it looks and whether I get enough image circle from them.
talk to these guys - they love to help people getting into stereo photography