Saturday, November 16, 2013

DIY Pentax Wired Remote

A sneak peak of the finished device

After the purchase of my Pentax K-7 a few years ago I began to experiment with long exposures, specifically "bulb" exposures. Bulb mode, sometimes abbreviated with a "B" on camera bodies, is a shutter speed setting that allows for extraordinarily long exposure times. When enabled, the shutter stays open as long as the shutter release button remains depressed. This is great since we can exceed the exposure times supported by most DSLR and SLR bodies. For instance the K-7 can do exposures automatically up to 30 seconds, but past this the bulb mode must be used. It is slightly annoying, however, since the shutter must remain depressed for the full duration of the shot. See how I solved this after the jump.

Oldschool SLR cameras used a manual linkage in the form of a shutter release cable. This allowed photographers to release the shutter without touching their camera, and a thumbscrew could also add bulb mode capabilities.

A manual shutter release cable for SLR Cameras. Notice the thumbscrew for bulb mode

As it turns out, a similar capability is available by using an external shutter release on modern DSLR cameras. Wireless and Infrared remotes are available for modern DSLR cameras, but they have the same problem that pressing the physical shutter release on the camera does: holding down a shutter button for 10 minutes, wireless or not, is impractical at best.

Lucking Pentax opted to include a wired shutter release port for just this purpose. Wired remotes are available for purchase, but are usually more expensive than they are worth and do not always include a "bulb mode" option, so I set off making my own.

The nice thing about this interface is that Pentax isn't doing anything tricky: no powered remote, no digital communication. Just plain old analog buttons wired directly to the camera. This allows us to customize the remote however we wish, and opens up huge possibilities for microcontroller based remotes. Here however, I will be building a very basic one with a few functions:
    • Autofocus button
    • Shutter release
    • Bulb exposure
    • Ability to extend cable
    Example circuit diagram for remote shutter release

I opted to use a standard 3.5mm jack instead of 2.5mm jack. This is because 3.5mm cables are plentiful in my spare cable bin, while I only have a single 2.5mm cable. I do, however, have a half dozen 3.5mm -> 2.5mm adapters (old cellphone headset adapters in my case).

2.5mm to 3.5mm adapter - The 2.5mm side plugs into the camera

Here is my parts list. Some I already had, so I will list below the RadioShack equivalents.

    • SPST Push On / Off switch
      • Red, Panel mount 
      • Model 275-617
      • Bulb mode switch
    • SPST Momentary Switch
      • Black, Panel mount
      • Model 275-644
      • Focus button
    • SPST Momentary Switch
      • Red, Panel mount
      • Model 275-646
      • Single shutter release button
    • 1/8" (3.5mm) Stereo Audio Jack
      • Panel mount
      • Model 274-249
    • 3" x 2" x 1" project box
      • Aluminum top for easy punching
      • Model 270-1801
    • 2.5 mm to 3.5mm adapter
    • 3.5mm stereo audio cable
    • Tidbits of wire
After punching the holes in the aluminum top, insert the buttons and screw on their retaining lugs. 

NOTE: If you solder the circuit together before  you insert the buttons into the panel and screw down their retaining lugs, you're gonna have a bad time. Be sure to do your soldering last. The exception is the 3.5mm jack since the retention screw goes on the outside of the enclosure. While I didn't make that mistake on this project, I've made it more times than I'd like to admit with heatshrink, powerpole connectors, and RJ45 jacks.

Solder up the switches according to the diagram above. I opted to use red for "fire" aka shutter release and black for focus. Having the focus button independent from the shutter release has proven to be invaluable, especially when operating from a distance. Although my remote is fairly simple, the possibilities are endless. Perhaps a TI wristwatch-controlled shutter release, or a DIY intervalometer. Mmmm...definitely future project ideas here.

A good example of what is now capable with the wired remote!
Evergreen Lodge - Yosemite National Park
Pentax K-7
Pentax SMC 28mm Prime @ F5.6
ISO 100
11 Minutes 08 Seconds


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