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In 2004, a few months after I bought my first DSLR, I started planning for its use in astrophotography and for that I needed an automated way to take sequences of bulb exposures. The Pentax DSLR i used had a socket for a cable shutter release that coincidentally was identical o some of the Canons i.e. a 2.5mm stereo headphone jack. Sure enough the Canon crows had already engineered an RS232 cable shutter release to be used by software, but these applications also relied on usb connections to the camera for other purposes. I couldn't find a good off the shelf solution so I decided to write my own program in VB6.
the DSLR Bulb Shutter Control was born. It still works and I used to take this picture (16x5min) + 5x5min dark frames.
However this old VB6 version relies on old COM technology that is outdated in the Windows 7 era even though still works, the picture above was taken via a win 7 64 laptop. Funny enough you can't just recompile old VB sources into .NET so I decided to rewrite the whole thing from scratch in VB.NET. Visual Studio 2012 is a pleasure to use and things have progressed significantly from the VB6 era.
The new version has a few extra features, most notably the MLUP Bulb exposure mode. In this mode, the software can trigger a mirror lock up and then after an arbitrary interval it will trigger the shutter. This is a feature of more recent Pentax cameras as opposed to the default 2sec MLUP. This way it become possible to give the system more time to dampen the mirror vibrations before opening the shutter.
BTW, the VB6 version will need the VB6 run time libraries, while the .NET just need the 3.5 framework (very likely to be on your laptop already if you are using Windows 7).
The usage for the new version is as follows:
connect the rs232 shutter release cable a serial port (native or USB to RS232 converter)
1) Button Check for valid ports--> This will scan all the available ports on the PC. Only these ports will be available to the "Serial Port to use" drop menu.
2) You should know what COM port is your cable connected to (check on the device manager->ports). Select it in the drop down menu.
3) Chose what exposure type (regular Bulb or MLUP Bulb). You also must set up these modes on the camera. For regular bulb you can add the 2secs MLUP (or whatever delay your camera is using). For MLUP Bulb you can enter the delay you want in the MLUP delay. Again, in order to use the MLUP delay, the camera must have this mode available, the Pentax K-7 and K-5 have it. Not sure about other cameras.
4) set up your exposure time, interval, MLUP and number of shots. If your camera is particularly slow at writing to the flash card (very old cameras) you can add that so the software will make sure the interval is not too short.
5) Once you are happy with the sequence, hit "Start Exposure"
6) At any point you can abort the sequence with the "Abort Exposure" button.
Both versions are attached below in the zip file.
Enjoy!
Vincenzo
Cable release designs are very common on the internet check a few links here:
http://homepages.nildram.co.uk/~sbuniak/AstroPhotog/Astrophotography_Canon_350D.htm
http://www.beskeen.com/projects/dslr_serial/dslr_serial.shtml
http://debianletters.blogspot.com/2007/12/long-time-remote-shooting-with-canon.html
You don't need anything fancy, the version with the optocoupler are better though as provide isolation from the PC. Note this software uses the RTSEnable pin of the RS232.
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