I use vintage 80's manual focus Minolta X-370 cameras for stereo photography. This entails using two cameras side by side and tripping the shutters simultaneously. The Minolta camera shutters can be tripped in the usual way with the finger switch on the top, or by a mechanical cable release in the cable release socket. Up to now, I tripped the camera shutters with a homemade dual cable release. But moving or changing the position of the cables introduced error in the synchronization, so I thought about tripping the shutters in a better way.

The X-series manual Minolta SLRs I'm familiar with utilize an electro-magnetic shutter controlled with an electronic circuit. While the cable release socket on the side of the body functions with a standard mechanical cable, I found that the cable release socket can also function electrically.

The cable release socket on the camera body has inside an electrically "hot" tab that, when grounded, trips the shutter.  So the shutter trip can happen in two different ways:

1) A standard mechanical plunger type cable release can be installed into the socket, and when you push the plunger, the cabke tip goes in, pushes the electrically "hot" tab to ground, and consequently trips the shutter.

2) An isolated electrical wire can be installed into the cable release socket with a conductive tip, and when you simply short the other end of the wire to the camera ground, the shutter trips.

Minolta had a remote shutter release system called the IR-1 which used a remotely held infrared source transmitter unit to trigger a receiver base unit placed near the camera body. The receiver base unit was attached to the camera cable release socket with an electrical cable. I have not seen this system first hand, but I believe the IR-1 electrical cable shorted the internal tab to ground.

After probing the tab inside my X-370 and shorting it to ground, I found that the electrical method works. I decided to make a pair of electrical contact mechanisms which plug into the cable release sockets.

Description

My concept is to position an insulated wire through a cable release ferrule (or jack) so that it touches the electrically "hot" tab inside the socket. The insulated wire can be wired through a normally open (NO) momentary switch to the camera electrical ground. The tab should now be easily grounded through the external switch to trip the shutter.

In considering a "homemade" cable ferrule with an electrical wire tip, it is important that the wire tip of the cable go deep enough into the socket to contact the tab, but not so far that it pushes the tab down to the electrical ground behind it. I'm sure Minolta had a specified length for the tip of the IR-1 "jack", but since I don't know it, I'll have to figure it out.

Rather than go through trial and error with different length tips, I devised a mechanism in order to adjust the depth of the wire tip as it comes out of the cable release housing. It is comprised of a nylon screw with an integral insulated wire which can be threaded in and out of the cable release jack. A standard cable release jack is used, but it is modified to incorporate a threaded bushing so the nylon screw can thread in and out.

The Details

First, I harvested a couple of threaded ferrules (jacks) from some regular ol' cable releases. The two I harvested were glued and the mechanical cables and tubes came off with a firm tug. The old glue was then cleaned out of the I.D. of the ferrule sleeve.

A threaded bushing (a 4-40 threaded hex stand-off) is affixed to the sleeve of a "harvested" standard cable release jack. One half of the I.D. of the bushing is drilled out in order to slip-fit over the cable release sleeve. The photo on the right shows the standoff with its bored out I.D. facing up.

The bushing is bonded to the ferrule sleeve.

The center of a 4-40 threaded nylon screw is drilled out to allow a solid core 22 AWG wire to pass through. I had access to an ancient mini lathe to drill out the screw, so I got fancy and drilled two different sizes to make a shoulder for the insulation to bear against. It would be fine to have the larger bore all the way through and just epoxy the insulated wire into the screw. The dashed lines shown illustrate the bore.

22 AWG solid wire is employed since it's stiff, and the O.D. of the insulation fits nicely in the bore of the cable release jack. The end of the wire which will contact the tab inside the camera is stripped to expose about 1 mm. The output end of the wire passes through the screw and can be terminated to your switch. The wire is bonded to the screw.

The nylon screw/wire assembly can now be threaded into the bushing and screwed in or out to adjust the depth of the wire relative to cable release jack.

Here you can see they have quite a range of adjustability for wire depth. It works fine, but after I was finished with this pair, I decided to scale down the gizmo and use a shorter bushing, and a shorter nylon screw.

On the bottom is a new smaller assembly; it's concept is the same, but it's shorter, and doesn't stick out as far. It'll be less prone to being snagged during use in the field.

Here is the device installed on my Minolta X-370. I have not yet wired the output wire lead to a switch.

To install and adjust the wire tip depth:

Before installing, back off the nylon screw/wire assembly so the tip is flush with the end of the "jack". Install the cable release jack firmly into the cable release socket of the camera. Advance the film lever and turn the camera on. Turn the nylon screw/wire assembly in until the shutter trips. This finds the limit of how deep the wire mechanically goes to push the tab to the internal ground. Back off the screw/wire assembly 1.5 turns. Backing off the wire keeps the tab from being too close to the internal ground, but not so far that the wire tip loses contact with the tab. You may have to experiment with how much to back off the nylon screw, especially with different "X" Minolta cameras. Once the wire tip is adjusted, it should not be necessary to adjust it again.

To test the cable release electrically:

Make sure the camera is on. Advance the film lever.  Using a switch or simply a jumper wire, short the cable release wire to the camera ground. The top metal cover as well as the bottom are case ground. The shutter should trip.

If testing is successful, you can now wire up any ol' type of switch you'd like.

I have not yet tried how a latching switch works on the bulb setting. I'll check it out and update...

Parts List:

• The "harvested" threaded cable release ferrules
• A 0.250" width hex standoff(bushing) x 0.375" length, with a 4-40 internal thread, or use whatever standoff/bushing you can scrounge.
• A 4-40 thread x 0.5" length panhead nylon screw
• A length of 22 AWG solid core wire

Links

Camera Ego I came across this website within days of coming up with my electronic cable release. The author came up with the same concept for tripping the shutter. The author also came up with a very cool remote release by using an RF doorbell kit.

Minolta Manual Focus This is a Yahoo Groups message board for fans of manual focus Minolta equipment. Several members were extremely helpful with my Minolta questions.

SFS