How to make a cable release switch for the istDL
I needed a cable release switch so I could start taking some longer exposure shots with my camera’s bulb mode. While searching the web to find a cheap one to buy I came across schematics for building a switch that would work for my camera. So I rounded up the needed parts from “The Shack” and set about building my own cable release.
The project was remarkably easy. Here’s what it took…
The cable release jack on the Pentax istDL accepts a standard 2.5mm (3/32in) stereo headphone plug. Unfortunately “The Shack” didn’t have any male/male 2.5mm cords. So I had to go for a 1/8in with an adapter to size it down to fit the camera’s socket.
I bought a 6ft 1/8in male/male stereo cable, cut one end off and striped back the wires.
I also bought a nice palm sized project box to put everything in.
Drill a hole into the end of the project box big enough for the headphone cable to feed through.
Now to make sure the cord doesn’t pull out of the project box you would ideally use one of those little plastic one way washers. I forgot to buy one, so I just tied a loose knot into the cord.
Next you need to drill holes for the various shutter control buttons. This switch will need three holes. Two for standard push button type switches and a larger one for an on/off toggle, more about those in a bit when I get to the wiring. To hold the top plate of the project box steady while drilling, I screwed it down to a 2×4.
The toggle switch needs a 1/4″ hole, so I worked my way up to that size with smaller drill bits first.
The 1/4″ bit made a pretty messy hole in the plastic project box, but with a little clean up the mess was hidden under the collar of the toggle switch. With the holes drilled I can install the switches into the holes I drilled. Here’s what it looks like from the under side which will end up inside the project box.
And here’s what it looks like from the outside.
Ok, now for a bit of explanation about the buttons/switches. I need to be able to control three different types of behavior. First the half button press which triggers the camera’s metering, auto focus etc. So there will be one push button that acts as if the shutter button was half pressed, that would be the black button above.
Next I need a button for a normal shutter release, like you pushed the button to take a photo. This is the red button above. Last, I want a toggle switch for bulb mode. To open the shutter the toggle would be switched to on. Switching the toggle back to off would allow the shutter to close completing the shot. Now you could just hold down the red button for as long as you want to hold open the shutter. But the toggle lets you lock the shutter open without having to keep your finger on the button for the whole exposure.
So what you need are preferable two different colored “NORMALLY OPEN” push button switches. It is very important that the buttons be marked “normally open” or “normally off” on the package. Normally open buttons are buttons that you push to make a connection. The alternative, “normally closed” buttons, you push the button to break the connection, which is NOT what you want!
And then you need one on/off toggle switch of whatever design you like. I went with one that was black and had a white dot marking the “ON” state so it will be easy to look and tell if you have the shutter sitting open.
Now to wire everything up. There are three wires involved. The ground (bare in my model), the ring (black) and the tip (red). To make the switches trip the shutter functions, you are basically just making one of two connections. For the half press state, the black needs to touch to the ground. To trigger the shutter, the red connects to the ground. In fact you can test things at this stage by plugging it in, switching the camera to bulb mode and then manually touching the corresponding wire together.
So the red wire from the headphone cable connects to tab A of my red button. Then make a small jumper segment of wire to go from tab A of the red button to tab A on the toggle. The black wire connects to tab A of the black button. Now the ground wire is connected to tab B of the red button. Then a jumper wire takes it from tab B on the red button to tab B on the toggle. So if either the red button or the toggle are switched the connection is made between red wire and ground and the shutter is triggered. To finish up, take a jumper wire from tab B of the toggle to tab B of the black button. This brings the ground end of the connection over to the black button, so if you press that button, the black wire connects to ground and the half press is triggered.
To finish, solder your connections, shove all the wires into the project box and screw it closed. Then plug it into the camera and shoot a way. Thats all there is to it.
The only draw back for bulb shots is you still need a watch of some sort to time out how long you have the shutter open. As a future improvement, I’m going to look into some kind of simple timer that I can maybe build into the switch so the toggle can be switched on and then the timer automatically breaks the connection when a set length of time expires.
