Describes the construction and use of serial port based control cables for computerized long exposure control of Canon digital SLRs. The motivation behind the development of the control cables is in astronomical imaging of DSOs, where DSLR exposures are typically required in the 5 to 15 minute range.
Note that this cable doesn’t replace the need for the camera’s USB port to be connected, as that is still used for focus and image download support. The cable simply provides computer control of the camera’s cable release mechnaism.
Alternative approaches for long exposure control include manual cable releases such as the Canon RS-60E3 (for the 300D/Digital Rebel), Canon RS-80N3 (for D60, 10D, 1D) and Canon’s TC-80N3 timer controller (for D60, 10D and 1D). You can convert the TC-80N3 for use with the 300D/Digital Rebel.
The serial port cable design provides several advantages over the parallel cable:
Can be used on modern laptops that do not have a parallel port.
Can be used with standard USB to serial convertors for laptops with no spare serial ports, or no legacy ports at all.
Most PC’s serial interface signals default to low, and for these PCs the there should be no dependency on the correct sequence of cable connections, programmatic resetting of the interface, and camera power on, in order to avoid random shutter firing.
The basic circuit is a little simpler, cheaper, and easier to build than the parallel version – mostly because we have been able to dispense with half-press (focus) control.
With a USB to serial convertor it can also be used to provide long distance remote control via USB CAT5 type extenders such as the Lindy, VPI or others. Use of a USB hub for both the USB to serial convertor, and the camera USB cable, results in only one cable having to be extended to provide full camera control.
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