Hi Geoff,
Good thread...it's something I've been thinking about for awhile too. Still not sure if I'll go yet, but if I do I'll be driving from Perth.
You're right, the light drops very fast near the end. I think the best option for high quality (given unlimited finance) is a high resolution cinema camera with lots of dynamic range like the Red Epic or Scarlet. That would be my dream. !!
http://www.youtube.com/watch?v=GZM5F...layer_embedded !!
Failing that, DSLR timelapse. The challenge then is firing off enough shots and changing the settings fast enough (as you say). Tests I've done with 5D2 + fast card (Sandisk), yields a maximum frame rate of about 1.2 fps. This is with 0.4 s continuous shutter and constant settings. The frame rate drops if triggering via the remote port...more like 1 fps. If triggering via USB frame rate is slower still.
Getting a nice smooth fall off in light over the last few minutes will be the biggest challenge, and may not be possible with a single camera due to DSLR limitations. Some things to consider-
Bulb ramping: If ISO and aperture are constant, you'll get about 4 stops of flicker free dynamic range. 1/30s -> 0.5s. I haven't done the calcs yet, but I think that 4 stops will be eaten up very quickly in the last 10 - 20 seconds before totality.
ISO, aperture stepping: This will expand your dynamic range, at the expense of frame rate. Best you can get if changing settings via USB is ~ 0.5 fps.
Fllicker: ISO and aperture stepping can be offset by adjusting bulb appropriately, otherwise 1/3 step adjustments will produce flicker. This may be difficult to adjust smoothly in post due to the big saturated blob in the frame. Exposure down adjustments are not possible once saturated. One way around this is to underexpose by more than 1/3 of a stop and always adust exposure UP.
Light Curve: Are any available for the last couple of minutes? I haven't looked yet, but I wonder if the drop is linear?
That's a quick summary of my thinking to date. Would love to hear others ideas on this.
Colin
ps. I have an automated exposure control system built around Eclipse Orchestrator + Netbook + custom microcontroller.