Canon Shutter Release Circuit for Astrophotography

Canon 20D Shutter Release Circuit - With DC Isolation

The following circuit provides an alternative to those normally used using a single NPN transistor to operate the shutter for bulb exposures.   This circuit uses a optocoupler to provide DC isolation between the camera and the shutter release circuit from the laptop.   In addition to the shutter release circuit shown here,   typically the camera will also be connected to an external power supply and to the laptop via a USB  circuit for data transfer to the laptop.  Depending on any of these external circuits and devices,  it is possible to get unwanted DC feedback loops that can cause the 20D to randomly lockup and behave in an unpredictable manner.   By DC isolating the shutter release circuit from all the existing circuits around the camera simply reduces the risk of getting into trouble and gives that extra level of protection to your valuable camera.