Avoid prism glasses for stereo viewing

[rjlittlefield]

About a week ago, dolmadis asked my opinion about some prism glasses for stereo viewing of parallel pairs. I was pretty skeptical about how well they would work, but I'm always on the lookout for useful tools so I thought I would give them a try. They arrived yesterday, and this evening I have taken a good look at their performance. Here's the report.

Good news:

• They fit over my glasses and stay on my face by themselves.

Bad news

• They add what I consider to be a completely unacceptable amount of CA.
• They cut sharpness and contrast.
• They have no adjustments for different size images or pair separation, other than moving closer or farther from the screen.

Summary: Avoid these glasses!

In my opinion, these things are a fundamentally bad idea, suffering further from shortcuts in manufacture. Much as I dislike red/cyan anaglyph glasses, I would much rather use those than these prism glasses.

To illustrate...

Here are the glasses themselves -- two thick plastic prisms mounted in a folding plastic frame.


Here is a setup to show what the glasses do.



This is looking through the glasses, with the camera placed another couple of feet back. At recommended 60 cm viewing distance, the glasses allow my eyes to look roughly straight forward and see a pair of images with about 8-9 inches between centers. (It looks like 7 inches in the picture shown here, but that's because of shooting with a single camera moved farther back. Through my eyes at 60 cm, it was 8-9 inches.)


Cropping closer on that same image, we can start to see the CA.


Then, to examine the image quality more closely, I set up at 60 cm away from my 22" monitor, used Excel to put a little black-and-white pattern on the screen, and shot the screen with a roughly 175 mm lens under 3 conditions.

1) Just the screen, nothing else in front of the lens. Pardon the moiré -- resampling pixels is always a bad idea.


2) The screen as seen through a Wheatstone type viewer that uses mirrors:


3) The screen as seen through the prism glasses:


I think you're probably convinced about the CA at this point, but since I have the images handy, here's a closer view:

1) Just the screen, nothing else in front of the lens.


2) The screen as seen through a Wheatstone type viewer that uses mirrors:


3) The screen as seen through the prism glasses:


I hope this is helpful.

--Rik

[dolmadis]

Hi Rik

More than helpful being an objective analysis from the perspective of my question.

I feel rather embarrassed having mooted the suggestion !!

BR


John

[rjlittlefield]

I feel rather embarrassed having mooted the suggestion !!

No need to be embarrassed. I bought my copy from http://www.berezin.com/3d/, whom I consider to be a highly reliable supplier of most things stereo. It makes perfect sense to think that the viewer would work fine. Alas, it does not.

My most favorite viewer has always been the bulky black unit labeled "3Dinlife Stereoscope" by the manufacturer, or maybe by some vendors -- I'm not sure who did the labeling. It is still illustrated at http://www.berezin.com/3d/3d_scope.htm, but unfortunately the manufacturer seems to have gone out of business and the units are no longer available new.

But I see that Berezin is now selling a unit that I have not tried, the "Pocket 3Dvu". The specifications look quite promising, so time to check out that one!

--Rik

[BugEZ]

I have used a PokeScope viewer to aid some of my pals at work in viewing stereo images. I don't recall lateral chromatic aberration in them and was quite pleased with them. I bought addional copies for my dad and son. I personally have no difficulty viewing the vast majority of stereo images (cross eye or wall eye) but suspect I may be an outlier. The PokeScope is set up for wall eye image pairs.

K


http://www.pokescope.com/pokescopeinfo.html#Design

[soldevilla]

I bought one similar to pocket3dvu in DX and vision is very good, no substantial loss of quality.

http://www.dx.com/es/p/mini-3d-stereo-v ... r496fE5S8E

but it seems that now this viewfinder is out of sale.

[rjlittlefield]

Berezin delivered my "Pocket 3Dvu" a couple of days ago.

In quick test, the image quality is excellent, as expected for a device that uses mirrors and not prisms. Optically, the PokeScope is quite similar -- again, mirrors and not prisms is the key to avoiding chromatic aberration.

Ergonomics are an issue with all these devices. Some are more flexible but more prone to go out of adjustment, some are better at masking out-of-frame elements, and so on. Some day I should haul out my collection of mirror based viewers and try all of them head-to-head.

--Rik

[dolmadis]

but it seems that now this viewfinder is out of sale.

If anyone is interested Amazon UK has one or two................

http://www.amazon.co.uk/Konetun%C2%AE-M ... 9MR9DHVMBP


Regards


John

[soldevilla]

as expected for a device that uses mirrors and not prisms.

Before to buy my stereo glasses, I built a viewer with four 90º prisms cannibalized from an old 7x50 binocular (telescope). It offer the same good quality that the mirror one. The clave is not prism versus mirror (first surface mirror!) but 90º prism or not.

[rjlittlefield]

If anyone is interested Amazon UK has one or two................

Amazon U.S. has them as http://www.amazon.com/Phetron-Mini-Ster ... B00MHKANXU. Search on "stereo viewer".

The clave is not prism versus mirror (first surface mirror!) but 90º prism or not.

Um, sure. But optically, those "90º prisms" are really just mirrors sandwiched inside a thick slab of glass.

I hope that readers of this thread will understand the difference between prisms that work by refraction, and the ones that you're talking about.

--Rik

[Smokedaddy]

Just wondering if there was anything new out that any of you has actually tried. I did visit the Berezin stereo website and his Facebook page. Sure don't need any more door stops.

Regards,
-JW:

[rjlittlefield]

I have continued to have good luck with the Pocket 3Dvu, http://www.berezin.com/3d/pocket_3dvu.htm , especially with new users (people not used to viewing stereo). The Pocket 3Dvu units that I received from Berezin back in September appear identical to the viewer that soldevilla mentions, right down to the script-FD logo on the front.

These viewers are just front-surface mirrors and a clear protective panel -- no lenses and not much light loss. They give a bright view that is compatible with glasses, and they have internal masks that are a good match for portrait layout images on prints and monitors.

The PokeScope is probably good for very experienced users, but it has lots of hinges that all have to be positioned correctly in order to work right. There's no way that I would take that thing to a conference. But I've now had quite a few people look through the Pocket 3Dvu viewers, and they were almost all successful.

--Rik

[Smokedaddy]

For whatever it's worth, I ordered a pair of the Pocket 3Dvu. They arrived the other day and I'm totally happy with them. Being new to all this I was absolutely blown away with my first stereo generated image. Pretty cool stuff.

[rjlittlefield]

For whatever it's worth, I ordered a pair of these ... Being new to all this I was absolutely blown away with my first stereo generated image.

I'm glad to hear that you've had success! I assume you're talking about the Pocket 3Dvu. I agree on both counts. Those are great little viewers, and I am regularly blown away by how much more I can see in stereo versus trying to make sense of 3D structure using shape-from-shading in a single image.

--Rik

[Smokedaddy]

My brain had to adjust and think for a second (you know, hey what's going on here) but then my eyes snapped into focus on the image I was viewing.