Timing Astronomical Events Using CHDK

UPDATE (December 2015): After many years of productive use (2009 to 2014), the digital camera featured in this page has developed problems and has now stopped working. Further development regarding this project is no longer possible.

While it is possible to time occultations and transits using a simple stopwatch, a better and certainly more accurate alternative would be to use a camera with a timer to time such events.

Fortunately, a simple setup for timing occultations and transits may be assembled using a telescope, an external video recorder, and a “hacked” point-and-shoot camera using CHDK, a free software that can greatly enhance the capabilities of a number of Canon PowerShot cameras by overriding its built-in (native) firmware (software).

In this article, I will describe how CHDK is used to “hack” a Canon PowerShot S3IS to show the camera’s system time on its on-screen display, a feature very much valuable for timing occultation events. This modification, however, is only intended to work with a Canon S3IS. CHDK is developed by dedicated programmers during their spare time, thus, there is no assurance that any particular camera will be supported. As of date, only a number of cameras can be used, a list can be found here. Special thanks to dedicated programmers Fudgey and Reyalp of the CHDK forum for writing the script (patch) used in this project.

Canon S3IS dedicated for timing astronomical events

The setup produces a final video output with timestamp overlay in the following manner: (1) Since pressing the camera’s “record” button will not produce a video with timestamp overlay and is currently beyond the capabilities of CHDK, the camera will only be used to “view” the object while at the same time “display the system time”. (2) An external recorder (say, a laptop connected to the camera’s video output) is then used to record the camera’s on-screen display, thus, producing the time-stamping effect.

Once you have a ported camera ready along with the correct firmware version (each model requires a particular CHDK version), you may now begin installing CHDK. Copy the software files on to the memory card (SD card), then turn the camera on by pressing “play” button. You will then be prompted with a menu in which you will have to choose the entry “firmware upgrade” to manually load CHDK. CHDK logo will be displayed momentarily as a confirmation that it is now running. If you switch from “play” mode to “shoot” mode, you will notice that there are now a number of new elements displayed on the screen: battery level indicator, available memory space indicator, and most importantly, the camera’s system time.

Note however that while the “time stamping” effect is achieved, accuracy nor precision cannot be guaranteed since the CHDK setup has never been compared and calibrated with a known time source (e.g., a typical video time inserter).

Once you get things running, you can then connect the camera to the recorder, and mount it to a telescope by means of an adapter. Shown below is a recent attempt to use the ‘hacked’ camera to time an astronomical event:

A timing observation for the 2012 Transit of Venus, as measured by our equipment. Photo Credit: Anthony Urbano, Ezekiel Rodriguez, Beb Jansen Poricallan, Carlo Ray Selabao, Criselda Roque. For more info about the 2012 Venus Transit, click here.

Related links: Lunar Occultation, Venus Transit, Occultation, Gallia Occultation

For tutorials on how to get started with astrophotography, click here.
For DIY astronomy projects useful for astrophotography, click here.
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© Anthony Urbano (Manila, Philippines)


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