time lapse

Iskra Valtcheva · March 7, 2005

hey, i am a student filmmaker based in austin, tx; and i'm involved in the shooting of an experimental 16 mm short which will include some time lapse footage of cityscapes. we are using a bolex H16; and renting an intervalometer from texcam, houston.

can someone who's had experience with time lapse give me some advice on how to shoot it? should i compensate in the aperture or shutter speed because of the single frame exposure? what do i do if the lighting conditions change? what else should i know? never done this before so any advice will be highly appreciated.

thanks!

~iskra

Josh Hill · March 8, 2005

Hey. I'm in Austin too. Also a student. I don't know much about time-lapse, but I have a couple of handy books and I'm sure we could figure it out.

I'm also shooting some 16mm coming up over spring break. We should talk. I believe my contact information is in my profile, and my e-mail addy is in my signature.

March 8, 2005

Ok well I've shot a lot of time lapse with 16mm so I will help you as best I can.

First off, you need to know the exposure time of the single frame unit you are using. When a cine camera runs at 24fps the exposure per frame is 1/48th, since the shutter is closed 50% of the time. 1/48th is quite slow in photographic terms, still photographers work with much faster exposures than 1/48th most of the time.

Now, doing a single frame the camera will not have time to get up to speed so we can safely assume that your exposure time will be longer than 1/48th. Hopefully the camera rental shop will know the exposure time, otherwise you'll have to guess. Assume maybe 1/30th? 1/30th is on my light meter so it could be on others.

Setting exposure for time lapse is more akin to still photograhy than cine since you are in effect shooting a long line of single frames. So dial in your film speed, I would use 50ASA for outdoor work during the day to cut down on the grain of 16mm. Under full sun at 24fps my meter shows an aperature of f-16. For a single frame you should be ok with F-22, assuming 1/30th. Although I have shot time lapse with my camera under full sun with 50ASA set at f11 and it came out fine. With 16mm always expose a little over, you can bring it down in post and create a "tighter" grain effect closer to 35mm.

Next is the intervol, for clouds do not exceed three seconds or the clouds will "jump" across the sky. Clouds move a lot faster than they look :-) For the setting sun, two seconds is more than enough, it sets very fast.

For street scenes your action will be plenty fast shooting at two seconds also. 240 frames will give you 10 seconds of finished shot. Most units allow you to dial this in as well.

Light leak is often an issue with many cameras set up for time lapse, although I think the Bolex will be fine in this regard.

For night scenes you can use 320 or 500 ASA. In these cases open your aperature as wide as it will go to shoot say a city at night. There is no risk of over exposure and you need all the light you can get to have the car headlights nice and brilliant. Again, adjust in transfer.

Now there is another technique where you leave the shutter open for two seconds for each frame, this gives you the light streaking look of car headlights. Used in a million commercials. For these shots I've actually used 50ASA as the two seconds is such a long exposure time.

How long will you be standing around for these 10 second shots? Well one frame every two seconds times 240 is 480 seconds divided by 60 is 8 minutes of shooting time.

If the light changes during your shot, ie a cloud moves over head, don't worry about it. It will be a slow process, the shot will get darker then light back up relative to the intervol. Some neat looking shots are achieved this way, don't try adjusting the aperature during the shot, you'll mess up your shot.

Top end people use a device called a Norris to maintain exposure, but this will be out of your budget range.

Does any of this make sense? :blink:

Richard

Iskra Valtcheva · March 9, 2005

richard,

thanks! this all makes sense and is VERY helpful.

a further question: there is a more complicated shot in the film where a single character walks at what appears to be normal speed while the landscape around him changes quickly. we are thinking of shooting it with time lapse while having the actor walk really really slow. how hard is it to pull this off?

another issue: what would happen if the camera moved regularly during small time lapse intervals? like, what if we mount it to a moving car? would it be complete and total chaos? or could it be beautifully choppy and fragmented?

~iskra

jon w · March 9, 2005

I shoot timelapse with a bolex, regularly. depending on which model you have, there is a switch that has a "T and I" on it, when you use the t setting the shutter will stay open as long as you hold the single frame trigger, the other one is just single frame with a shutter speed of 1/30 sec (dont quote me, check the net) but your shutter speed stays the same (shooting single frames) regardles of what your fps dial reads.

make sure the little door in the viewfinder is closed!!

also, focal length is also a factor when determining your intervals, a nice wide angle shot of the moon arking through the sky at 1 frame every 15 seconds, the moon may only show up in 2 frames if your shooting at that same speed with a telephoto. rule of thumb: wider lens=longer intervals, longer lens=shorter intervals.

March 10, 2005

a further question: there is a more complicated shot in the film where a single character walks at what appears to be normal speed while the landscape around him changes quickly. we are thinking of shooting it with time lapse while having the actor walk really really slow. how hard is it to pull this off?

I doubt you'll get this to look "right" what you'll end up with as a FX shot that you say to people, "we meant it to look that way." Normally these shots are done with green screen, shoot your actor in real time against the green screen. Then composite in the time lapse back ground. This can be done with Premiere or FCP easily enough.

"another issue: what would happen if the camera moved regularly during small time lapse intervals? like, what if we mount it to a moving car? would it be complete and total chaos? or could it be beautifully choppy and fragmented?"

Mounted to a moving car might not look too bad. I did this shot once and got a "flight of the bumble bee" type of look. Use a short intervol of one or two seconds to smooth it out.

And I second this from Jon W.

rule of thumb: wider lens=longer intervals, longer lens=shorter intervals.

Good point Jon.

Richard