Automatic Eclipse Photography

This brief article describes the camera system which I used to automatically photograph the Total Solar Eclipse of 2008 August 1 (from the Xinjiang Uyghur Autonomous Region of China. This is the second version of the system that started life on a Psion 3, controlling 35mm film cameras, as documented here.

There are four hardware elements to the system:

• a Borg 101ED telescope, Vixen equatorial mounting and peripheral equipment
• an Asus Eee PC computer
• a Canon 40D DSLR camera
• and a Garmin 12XL GPS unit

There are several software elements:

• the 'Open Source' camera control program gPhoto2
• a controlling Perl script
• a C++ program 'eclipse' to calculate local circumstances
• SQLite database management system

Asus Eee PC The Eee PC runs the Linux Xandros operating system. gPhoto2 and the Perl script run on the machine controlling the 40D camera via both a USB and serial port connection. The Perl script reads a series of commands from a 'data' file and translates them into instructions which are sent to the camera. Example commands in the data file include 'set shutter speed' and 'fire shutter'. Commands may be either executed immediately, or at a set time and are stored in the SQLite database. For those interested, the Perl script is available here. To arrive at precise times of 2nd and 3rd contact, the program I wrote for the Psion to calculate 'local circumstances', based on the algorithms in Jean Meeus' book 'Elements of Solar Eclipses 1951 - 2200', was translated into C++ and compiled for the Eee PC. Limb profile corrections were estimated graphically from the diagram in the NASA Solar Eclipse bulletins.

Canon 40D DSLR camera

The Canon 40D camera contains a 10 megapixel APS-sized CMOS sensor. It has 'LiveView' which proved invaluable in achieving precise focus. The Eee PC had connections to both the USB and remote switch sockets.

The 2008 August 1 Total Solar Eclipse

For the eclipse I used the 40D attached to a Borg 101ED refractor with a 0.85x field-flattener mounted on a Vixen Super-Polaris equatorial head. Prior to 1st contact the internal clock on the Eee PC was set to UTC from the Garmin GPS 12XL via the serial interface. The coordinates for the observation site were also read from the 12XL and entered into the SQLite database for use by the program that calculated the local circumstances.

The camera was fired for three sequences during totality: the first run was from just before 2nd contact to capture Baily's Beads, to 15 seconds after, for recording the chromosphere and prominences. Exposure times ranged from 1/1000 - 1/60 second. During the middle part of the eclipse a sequence of exposures lasting from 1/250 - 4 seconds was taken to capture the inner, middle and outer corona. The third sequence was around 3rd contact to once again capture prominences, the chromosphere and the diamond ring.

Pictures may be found here.

References

Glenn Schneider has an extensive article about his system based on a Macintosh, at http://nicmosis.as.arizona.edu:8000/ECLIPSE_WEB/UMBRAPHILE/UMBRAPHILE.html, and for Windows users Fred Bruenjes' Orchestrator software was used to control many cameras along the 2008 eclipse track.

Please get in touch if you have any questions or suggestions.

2008 November 11