Saturday, July 15, 2006

Inexpensive Night Intervalometry with the Digital Rebel XT

 I recently discovered two interesting things:

  1. Canon's TC-80N3 intervalometer ($130ish) makes it possible for their mid-range (EOS-20D, EOS-30D) and professional (EOS-5D, EOS-1D) digital SLRs to take exposures at timed intervals.
  2. Canon's low-end digital SLRs, including the Digital Rebel XT (EOS-350D) I use, are not compatible with the TC-80N3, and third-party solutions like the Zigview R are quite expensive ($250+).
However, whilst poking around last night, I pieced together three other facts:
  1. The Digital Rebel XT supports the RS-60E3 ($20ish) remote switch, which I have, for "bulb" releases to prevent camera shake, or to arbitrarily long exposures.
  2. The XT does timed exposures up to 30 seconds, and can do long-exposure dark frame subtraction for anything over 1 second at ISO/ASA 1600 or anything over 30 seconds at lower ISO/ASA settings, taking as long for the subtraction as it does for the timed exposure.
  3. The XT has a "motor drive," and will cheerfully take one shot after another.
So I plugged in my RS-60E3, set the XT for ISO/ASA 1600 and 30-second timed exposures, with dark frame subtraction on, found an aperture that kept things from being too bright, and locked the RS-60E3 in the "on" position, just as I would do for a "bulb" release longer than 30 seconds.

It did a 30-second exposure, followed by 30 seconds of dark frame subtraction... followed by another 30-second exposure, followed by another 30 seconds of dark frame subtraction... I walked away and let it do its thing.

You can see the results of this in two short time-lapse videos I made:
Giant Space Laser Time-Lapse
UH88 timelapse

Each of these is about 36 minutes of real time, at one exposure per minute. Tonight I hope to put together some significantly longer time-lapse sequences. I may opt to leave out the dark-frame subtractions, to get 2 30-second exposures per minute, or I may go with a wider aperture and use 15-second exposures... wait and see.

So, basically, if you're willing to limit yourself to taking N-second exposures every N seconds (or every 2N seconds if is 30 or you're using ASA 1600 and N is at least 1), the XT and its cheap bulb release provide some basic intervalometer functionality. It's not terribly flexible, and the requirement for long exposures makes it pretty useless during the day, but in the dark of night, the results can be quite nice.

This may also work with the original Digital Rebel (EOS-300D), but I don't have one of those to try it out on... anybody have one, and an RS-60E3, and want to give it a try?

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