Timelapses: controlling aperture by hand and avoiding flicker

Started by PaulJBis, February 15, 2014, 09:18:17 PM

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PaulJBis

February 15, 2014, 09:18:17 PM
Hello:

I am using ML 2.3 (the stable version) on a 550D, and I'm testing the bulb ramping feature to make sunset timelapses. I have it set on the "sunset" mode, and I also have the manual exposure ramping set to -0.01EV per shot, so that the final night shots are a bit less exposed than the daylight ones.

Anyway, after some trial and error, I managed to get an excellent timelapse without flicker, but today I decided to try it again while opening the aperture by hand at given intervals. I started at F18 and 1.5sec. exposure, and when the scene got darker I opened the iris manually to F14, then to F9 and then to F8.

I expected that, when doing that, the bulb ramping would automatically adjust shutter time to compensate for the changed aperture, but it doesn't do so: if a shot has F18 and 3sec., after I open the iris to F14 it still takes the next picture at 3sec. (with no ISO change). As a result, there's noticeable flicker when I make those changes.

My first question: is this normal? What am I supposed to do to avoid this?

Aside of that, in today's timelapse there was also some higher-frequency flicker that wasn't there in my previous one (both shot on the same location). After having a look, I noticed that the center of the shot had an object that moved slightly with the wind and was directly lit by a streetlight (the center spot metering mark was right on it), so its brightness varied slightly. Could this have caused it? Basically, what I'm asking is: does bulb ramping use the spot metering feature of the camera to measure light?

Thanks in advance.

PaulJBis

#2
February 16, 2014, 10:00:19 PM
Hey, I didn't know about that Bridge script! Very cool. I'll use it in the timelapse that I mentioned and see if I can remove the flicker.

As for the rest... I am aware of your work in the new adv_int.mo, and I'll definitely be trying it when I'm finished exploring the stable release and start with the nightlies, but in the meantime... is the behavior that I described normal for 2.3? (i.e., not reacting to aperture changes from one frame to the next). Also, does it use spot metering for measuring light?

I'm not asking this just for practical reasons, but for my own intellectual curiosity. Basically, I'm trying to understand how does the bulb ramping work internally, what factors it uses to decide what to do.

dmilligan

#3
February 17, 2014, 06:12:38 AM
I'm not very familiar with that feature. I never used it, it's been gone a long time. But I'll try to answer your questions:

No, it probably doesn't respond to changes in Av (I think it's just expecting that you leave the camera alone)
No, it doesn't use spot metering. ML has no access to any of the Canon metering data AFAIK. I think it works by actually analyzing the image data after each picture is taken (so basically the exposure for the next picture is chosen from analysis of the previous)

PaulJBis

#4
February 17, 2014, 03:45:00 PM
Thanks for your answer. I was doubtful because the user guide seems to imply that it's okay to change aperture while using bulb ramping... but then again, the user guide also says at the top "for 2.3 stable release", and then it contains a section about AutoETTR  :)

I'll definitely be using your module soon.
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