Sometime ago I stumbled on a Youtube video of Matt Molloy's interesting photo technique. Similar in nature to startrails combination shots, timelapse light painting/time stacking is also a result of a number of photos merged/blended together. However, in comparison to startrails photography where you simply follow the movement of stars around a particular subject, with your only worry having to compensate for "light pollution", I found the light-painting is a bear to deal with.
First of all, the light from day to day is never the same. You have to have clouds, which always move unpredictably. Cloud formations are never the same and you could never take the same timelapse photo, even on consecutive days. While cloud movement requires some sort of wind, your subject have to remain absolutely still (think of tree branches, cars on the road, water ripples, etc) for extended periods of time.
You constantly have to anticipate what the light is going to be like at the end of the shoot or where the clouds will flow to or how quickly the sun will set, because once you set your WB, eV, Tv, and ISO, that's it. If you "guess-timate" your shutter sped or ISO incorrectly you will waste at least two to three hours of your day... each time.
In my experience, just the preparation for timelapse light-painting is a science in itself, and an inexact science to boot. There's no magic number, there's no "rule-of-thumb" - it is all trial and error. Last year I took a couple of stacks but they were all hit and miss, none satisfactory. In the last couple of months I took a few more attempts again. Here they are.
Equipment: Canon 7D, Tripod, Intervalometer, EF-S10-22mm f/3.5-4.5 USM and EF17-40mm f/4L USM.
Software: StarTrails 2.3, StarStaX 7.0, Advanced Stacker PLUS 14E, Photoshop.
That's it. Enjoy!
Burruss Hall (January 5, 2015)
The above photo is a stack of 258 photos. Something to think about - do you really have to have many frames to get a good result? Well, here's a timelapse with only 150 photos from the same sequence as above... You be the judge which one is better.
Burruss Hall (January 18, 2015) time stack of 406 photos. If I am not mistaken, ISO 500, 1/200s, Advanced Stacker PLUS 14E.
Duck Pond (January 25, 2015) time stack of 154 photos. This one was fun. I got a bit lucky as my camera's shutter speed was set to 1/400s from the day before. If I had paid attention to it, I would have set the speed to something like 1/160s or 1/240s. "Better lucky than good", I guess. Like I said, it is all trial and error. :-)
By the way this is what the sunset looked like at a different angle from my second camera (single shot), Tv 1/125s, ISO 800:
Click on this link to see Timelapse Photography, Part II (February, 2015)