Alternating under-exposure during intervalometer timelapse when shutter >3 sec.

Issue #2169 new
BBLeo created an issue

I'm using magiclantern-Nightly.2014Oct07.550D109.zip on my 550D. I've done many timelapses without problems using exactly the same settings and procedure until upgrading to the latest ML. I left my camera doing a three-day timelapse, taking one photo (JPEG) every 40 seconds and plugged into a DC coupler. I set the ISO at 200 (with highlight tone priority), exposure compensation -1.0EV, and the aperture at f/8.0, and partly un-screw the lens to save wear on the aperture blades (which also locks the focus too). I use aperture mode, so that the camera automatically varies the shutter speed as required. (Perhaps I should use exposure ramping but I'm just using auto-exposure for now and blending frames together.)

The intervalometer works as expecting during the day but as soon as it gets dark the exposure behaves strangely: Every second picture appears correctly focused, but the pictures inbetween are very under-exposed (e.g. 4 second shutter speed (according to EXIF) when the normal photo is 20 seconds). The transition shutter speed is about 4 seconds - as soon as a longer shutter speed is used the next photo has a strangely short shutter speed. This lasts all night until the shutter speed falls below 4 seconds at dawn. At the transition point the exposure is only jumping between 4 and 3 seconds, or 4 and 2 seconds.

I cannot find any reason for this to happen, and I believe I am using exactly the same settings as with previous ML versions, and I can't find anything odd in the ML menus. I therefore think this is a bug - somehow the ML intervalometer is messing up exposure settings or shutter speed when it is dark.

Comments (5)

  1. BBLeo reporter

    This is still happening 2 months later, now using 2nd March 2015 build. This is really wasting my shutter!

  2. Alex

    ETTR or other auto exposure tools from ML enabled? If so, what settings?

    The intervalometer, by itself, does not alter exposure settings.

  3. BBLeo reporter

    Thanks for your reply, A1ex.

    I'm not using ETTR or anything fancy. As far as I can see, the only setting I'm using are the only settings I'm using are the ones described above, plus "Cloudy" white-balance setting, mirror-lockup, and the neutral picture style with adjustments. There's no HDR settings or anything. Apart from this all I do, copied from above, is:

    "I set the ISO at 200 (with highlight tone priority), exposure compensation -1.0EV, and the aperture at f/8.0, and partly un-screw the lens to save wear on the aperture blades (which also locks the focus too). I use aperture mode, so that the camera automatically varies the shutter speed as required."

    For some reason, the intervalometer function results in two photos being taken during even normal interval, once it gets dark. This seems to be a bug - I can't think what else could cause it.

  4. BBLeo reporter

    Just for clarity - it seems to take one photo correctly, but for some reason take an unexpected underexposed photo too during every interval - and I haven't noticed any problems with it doing the reverse during the day - i.e. no underexposed ones in bright light. It is completely consistent - pairs of photos during every interval all night, then switching back to normal at dawn.

  5. Alex

    Can you upload your SETTINGS directory, so I can try?

    A video of the camera screen might be helpful as well.

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