[photo-3d] twinning pentax SLRs

["Chris Pickering" <chrisp@xxxxxxxxxxxxxxxxxxxxxxxx>]

I am relatively new to stereo photography and this is my first posting to this group so please don't be too harsh if I make any basic errors.

I think the ZX-M may be called something else here in the uk, but I don't know what. Do they have the usually sockets for the electronic remote release cables, known as "cable F" ?

I have recently twinned two Pentax MZ 50s using these cables. The Wladyslaw Reksc quote isnt particularly clear, but it suggests that "there is no need for any additional hardware". Unfortunately I cannot agree with this. When I unsoldered the switch from one cable release and soldered both release cables to a single switch I found that the cameras would focus and fire off many times willy-nilly without me touching the switch - and they weren't even firing simultaneously !  I am not the only person to experience this - it is also noted in an article in the uk Stereoscopic Society Journal by someone who twinned two pentax SLRs - he eventually got pentax to connect the cables for him, by finding some way to keep the cirtuitry separate. With a little effort I managed to do the job for myself. 

Although people say that there is an inherant imperfection in twinning remote releases rather than the cameras internal electronics, I could get two SLRs with TTL, AF and electronic remote release sockets quite cheaply, since the MZ 50 is being phased out. Complex internal electronics, a disadvatage of 21st century technology, can thus be overcome.

I have also made a twinning bar to hold the two cameras together, with the new switch in one of two handles that can be removed to make it easier to pack away and to remove the switch from the bar during long exposures. As far as I can tell the shutters fire more or less simultaneously - I suspect that any deviation is even less than the difference between the nominal and actual shutter speeds. But in low light the AF feature takes different lengths of time and you have to wait for both bodies to complete their task (indicated by a handy little beeping noise), but this only really happens in light so low that there will be difficulties with the exposure anyway. Side by side there is a separation of 143mm !  But I can always mount them differently - base to base, one behind the other, etc. I have just got back the results of my first roll of film and they seem ok, although I haven't had a chance to look at them properly. (I use the over-under format). They certainly have far le!
ss to crop off the edges than se
rial shots from a single SLR. 

The cable release socket on the camera body has a clipped corner, ensuring that the plug on the cable can only be connected the correct way around. There are three pins in the socket. The pin at the clipped-corner end is the "common" terminal, enabling circuits to be completed, and is taken to the remote release switch by the black lead in the cable. The middle pin is the AF connection, which connects to the switch via the blue lead. The pin at the non-clipped end is the shutter release connection, which is connect to the switch via the red lead.

However (and this is where the problem lies) the three positions of the pentax switch are not a) off   b) AF  and  c) shutter release  but a) off   b) AF  and  c) shutter release AND CONTINUOUS AF !   And this is somehow done without making a short between the AF and shutter circuits (dont ask me how).

I had to get around this by buying a "4 pole 3 throw" switch from Maplins (I dont know if they trade in the US) - order code FH38R. This is basically four switches, each with three positions, operated by a single lever. In this way I could connect one camera to one set of contacts, the second camera to another set of contacts, the continuous AF function (useful for action shots) to a third set of contacts (in such a way that it is switched on at the same time as the two shutter releases are switched on), and the final set of contacts are redundant (I could not find a 3 pole 3 throw switch).

I hope this doesnt sound too garbled. I can explain further on or off group if anybody wishes. And, since there are 16 contacts on the switch, I could try to create a graphic (I don't have a scanner so I can't just digitise a rough drawing). Basically, anybody who can use a soldering iron can twin two pentax's without even touching them let alone taking the guts out !

Chris Pickering


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