Timelapse exposure time

[Juha Kinnunen]

Hi,

Have any of you experienced that the exposure time wouldn't be constant during timelapse?

We have a customer who shot with 1/12 sec exposure time, 1 frame 5 sec interval. Tungsten lights. Fixed camera,-lights,-everything.

In playback you can see slight change in luminance- about 1/3 stops. Luminance changes few times during take. Same luminance level holds several frames, so it's not jumping randomly.

After seeing this material in Red Cine, I can not say what caused this. Is it change in exposure time, studio light or what? Is there any way to analyze the shot frame by frame to know what happened in camera? Metadata?

Personally I like to think that there was slight voltage change in electrics that affected to studio lights. Maybe some one with more experience with TL have similar experienses?

regards,
Juha

[Juha Kinnunen]

I made few test with same TL settings as above.

Tungsten light - steady luminance in playback.
Tungsten light dimmed down- luminance changes in playback.

When shooting 25fps with 180° shutter the dimmed down luminance look steady in playback.

[Vigen Vartanov]

Can you share footage , it looks like not stable power source.
I never have problem like this with TL .

[Russ Fill]

Are you using 120 or 220 volt 60 or 50 cycles??
I do a lot of time lapse and the one thing that causes what you talk about is the change in lighting. Maybe the cycle is affecting it very slightly and the only way you really see it is when you take a frame from the most drastic change in the lighting situation. They could have a much larger shutter angle and this might fix or reduce the affect... Say 270 or even 360. I know that changes how the image looks but it will allow the changing of a light to be over a greater period of time.

[Dalibor Fencl]

Yes, that's unfortunately not uncommon problem of animation generally. Tungsten lights varies slightly over longer period of time due to changes of voltage in ordinary outlets. Also the dimmers may cause the same effect. One can't see it by eye, nor the camera while in normal speed.

Have a luck.

[Juha Kinnunen]

It's 50Hz here.

I tested different dimmer levels with tungsten. This problem occurs only in very dimmed light levels.

This problem has nothing to do with Red's time lapse.

Thanks

[Russ Fill]

It's 50Hz here.

I tested different dimmer levels with tungsten. This problem occurs only in very dimmed light levels.

This problem has nothing to do with Red's time lapse.

Thanks

Try using a fully powered light and dimming it down with ND or using some gels to get the color temp you need. We just had the same problem this weekend when shooting hight speed. The bright 2ks worked fine but the smaller 150's had some dimming going on so we used the larger lamps that can hold the brightness in between the current cycle. And just knocked them down with ND and some CTO to get that dimmed effect...
Good luck.