Stereo SLR with Pentax K
What I didn’t like is that I lost both the meter and the rangefinder function due to some “accidents” during the making.
While it would have been possible to correct this with another go at two more cameras (and no accidents), there is also the fact that the Dacora lenses are not quite as good as I had expected. I remembered them to be quite impressive, but this was maybe just my glorifying memory, the first slides were a little dull indeed and more modern lenses definitely perform better.
So, even if for a rangefinder of the sixties the lenses may be alright, better is the enemy of good…
On top of that, 45mm as the only focal length is too long for my taste anyway.
Since I like the RBT cameras very much, the next DIY project came around: A Stereo SLR with Pentax K mount (there are still a couple of Pentax lenses in the cabinet, even two 28mm).
I would have preferred to use two genuine Pentax bodies, but their shutter layout turned out to be too wide to achieve the desired stereo base of 75mm. I especially looked at the MX (that would have been nice!), but the MX is absolutely cramped with mechanics; nothing can be sawed off there without also taking away the camera function.
I went for a base of 75mm, to be able to stay with the original 24x36 format and not to waste too much film. 75mm may be a little wide in theory, but I meanwhile believe that this has not much of an effect for everyday photography.
Apart from Pentax cameras, there are many other camera bodies around with Pentax K mount, from various brands, but many of them immediately disqualify as being too wide. RBT used the Cosina C1 body (among others), closely related to the Voigtlaender Bessa cameras and this is what I eventually also did.
The Cosinas are very straightforward cameras, no mechanical marvels, but their construction is pretty logical and they are easy to dismantle. Actually, I cannot remember a single camera that looked so “neat and clean” inside – kudos, Cosina!
Below picture shows both halves after cutting the “donor” cameras in two:
And after glueing them together:
As for engineering skills, RBT demands greatest respect. I haven’t even held a RBT, nor used or seen its innards, but they actually offered such a camera for the full 24x36 format with a stereo base of 65mm. How on earth they succeeded to move those two cameras closer to each other yet another centimetre (and keep the function!) is beyond me.
The RBT cameras also have all functions integrated, i.e. film transport and shutter tensioning is done with one lever, only one release button releases both shutters and only one dial is used to time both shutters – very impressive.
Transporting the film as such is a simple task, since the camera only uses one film. Establishing the correct positions is more difficult: stereo pairs are exposed at the positions 1/3, 2/4, 5/7, 6/8 and so on, and RBT cameras are able to control this, but my camera does not (and I also don’t know how RBT did it). On my camera, the film needs to be transported to the correct positions marked on the frame counter, with the brain switched on, no beeps or flashing red lights will warn if this is not done correctly.
The shutter of the neighbouring camera is cocked via a flat piece of aluminium on the underside of the camera, and I assume that RBT did it the same way, since their camera also has a doubled-up bottom cover, just like mine.
To trip the shutter with only one button I have manufactured a small cable pull, with one redirection, to gain some cable travel.
I wouldn’t be surprised if RBT had followed the same principle, but I don’t know.
RBT cameras also have only one shutter speed dial – and I again have no clue how RBT has managed to also operate the other shutter with this dial. My camera has two dials and that is also sufficient, I believe. Stereo Photography is “slow food” anyway, so investing that little extra effort to check both shutters are in line should be possible.
I have also decided to remove the prism of the “second” camera. While it is nice to see through both finders at the same time and preview the stereoscopic effect, the second prism adds weight, and I also liked the idea of having an asymmetric camera.
Here you can see the top and bottom covers before painting:
And this is the finished camera:
Coloured cameras are en vogue…
The paintwork is awful, this is something I am just not good at, but I promise to try and redo it some day.
Technically, the camera works well, including the cable pull shutter that I first didn’t believe in.
The first stroke of the lever cocks both shutters and transports the film by one frame. Depending where you are on the film, up to two more strokes are needed to transport the film to the next marked position on the frame counter, to be ready to expose the next stereo pair.
Metering is unchanged as compared to the original camera, with LEDs in the finder, as well as focusing. The set values have to be transferred to the other camera. I will maybe also try and couple some zoom lenses, but until then this is sufficient.
The first film showed some light leaks, that I have to find and stuff now (I have an idea of where to look already). The exposure of both cameras is somewhat different, but that I also attribute to the light leaks, until proven otherwise.
Some pictures from