Re: [photo-3d] Are beamsplitters crappy?

[Mike Kersenbrock <michaelk@xxxxxxxxxxxx>]

"John A. Rupkalvis" wrote:
> 
> What are you guys talking about?   To my knowledge, Pentax never made a
> beamsplitter.  They did make some image splitters that split the image into
> two, narrow side-by-side images.  But a beamsplitter doesn't do that.  As I
> have explained many times, a beamsplitter requires two cameras at 90 degrees
> from each other and 45 degrees incident to the surface for stereoscopic
> photography.

The front-surfaced mirror image-splitter is meant.

If you read my posting below carefully, you will see that I don't
directly say that Pentax made a "beamsplitter" (althought I did
imply it).  Also note that in the post-script I called it what Pentax
called it: "Stereo adapter".

That said, technically you're correct.  It has been disccussed many
times on this mailing list over the years.  However,
the mirror based image splitter has been called "beamsplitter" not
only by this mailing list, but it's called that in the literature
(like books,etc) of the 50's as well.  So with a half century of
misnomer, I think a dictionary publisher would put that definition
into their book (much like the word "hacker" was redefined by
misuse, although that took only a few days to redefine).  I think 
I'm getting too old.  I give up fighting these fights much quicker than 
I used to and I now just go with the flow so long as I know what they meant
(which I didn't find to be the problem you did).  :-)

Mike K.


> 
> A beamsplitter permits full size (full width and full height) images.  Good
> quality beamsplitters are AR coated, and transmit about 48% of the light and
> reflect about the same (depending upon the efficiency, around 4% of the
> light is lost in absorption).
> 
> JR
> 
> ----- Original Message -----
> From: "Mike Kersenbrock" <michaelk@xxxxxxxxxxxx>
> To: <photo-3d@xxxxxxxxxxx>
> Sent: Tuesday, January 09, 2001 2:12 AM
> Subject: Re: [photo-3d] Are beamsplitters crappy?
> 
> > Bryan Mumford wrote:
> > >
> > > Would
> > > others agree that beam-split pairs are unsatisfactory?
> >
> > Depends upon what one is using them for.  While I don't agree that
> > they are crappy, I do agree that they have significant restrictions
> > in their use, or at least my Pentax one does.
> >
> > > about it this way before, but I'm getting four times as much picture
> > > data in two full frame cha-chas than I would get in a single frame
> > > split image. Maybe a beamsplitter is not a worthwhile project after
> > > all.
> >
> > In terms of amount of film you get exposed, quite true. But a
> > "beamsplitter" (image splitter) can take the two images at
> > the same time (and with perhaps a 1/4000 sec shutter if light is
> > bright enough) -- something a cha-cha has no hope of achieving.
> > "Beamsplitter" also probably would provide better rotational
> > alignment between the two images (one thing I certainly never
> > seemed to be able to do too well when cha-cha'ing with my wife's
> > digital camera).  :-)
> >
> > I'd call it a step up from cha-cha's, but most any stereo camera would
> > be a step up from the beamsplitter (except only for some special niche
> > circumstances).
> >
> >
> > Mike K.
> >
> >
> > P.S. - When I was married mumble years ago, I had a friend use my Pentax
> >        stereo adapter, and his photos are loved by us more than the ones
> done
> >        by the professional (and not just because it was 3D, the image
> content
> >        was important too :-).
> >
> > >
> > > Bryan Mumford
> > > Santa Barbara, California
> > > http://www.bmumford.com
> >
> >
> >
> >