Re: Achromatic StereoScope

[P3D Alan Lewis <dlewis@xxxxxxxxxxxx> To: photo-3d@xxxxxxxxxxxxxxx]

P3D Dr. George A. Themelis wrote:
> >
> This discussion made me curious enough to open and take apart the lenses in my > Keystone 46B Visual Survey Telebinocular. > Unlike every other stereoscope that I have seen, this one has no > chromatic aberration and delivers pin-sharp images. I did a side-by-side > comparison and concluded that the images are sharper, there is no chromatic > aberration, you can see far away and enjoy the stereo image more than any other > viewer. A couple of lucky owners of this rather rare sterescope agreed that > this is the best they have.

I remember the discussion on this list. I have seen a couple of metal Keystone viewers (the library pedestal and the hand held telebinocular that stores in the fake book). Is the model you mention one of these? In John Waldsmith's "Stereo Views" book he lists a Keystone telebinocular ,metal,viewer that came in a booklike box and adds that it has excellent optics. Is he referring to achromats? Or is yours a vision testing instrument rather than the typical consumer models? Do you know about what year your viewer was offered? 

> I am holding one lens in my hands right now. Sure enough, it is made up from > two elements. I do not know if it is an achromat cut in half or a specially > designed two-element lens. The size is 33 mm in length and 22 mm in center > thickness. As I said, this lens delivers the best image I've seen in a > stereoscope. Alan, I can send you the lens to examine if you want... 

Good job studying the lenses, very informative. The thickness (22mm) is close to my lenses (around 7/8"), really thick and heavy! The 33mmlength is typical for a Holmes scope lens. You may be able to tell if it was cut from one piece if you can see sawing marks on the "fat" edges (the fat edges go together to form what was a single lens, since it was bisected).
If it was ground from two separate pieces then I would expect to see a molded edge rather than a perfectly flat sawcut edge. Thanks for the offer to send them to me, but I'd rather you don't. I shudder to think that they could get lost or damaged.


> I would personally pay the extra difference and get a viewer with better > lenses. I am sick and tired of chromatic aberration! I know I am not alone. > Once you get used to seeing pin-sharp and color-free images you don't want > to go back to single lenses.

That's what happened with the Holmes achromat viewer prototype. It's the only viewer I want to use now. I was happy until I built the darn thing. ;-) I would love to be able to offer an achromat scope as a continuous product. When I run out of lenses I'll go into a depression. 

On a related issue, the superior images only show up my next problem..... better prints! It is very difficult to get a truley sharp print on a consistant basis. The negatives are sharp, but the processors are not.
To solve this problem (and the lack of ortho prints using a Realist negative) I am now building a stereo view camera to take a pair of full size (3" x 3") prints and/or negatives. Using a 5 inch lens will get me very close to being ortho and the full size neg. will be sharp (if I can focus , of course). Boy, pursuing the perfect print/viewer combination in the Holmes format is a huge project. And this camera will be far from portable too.

Alan Lewis


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