EOS R6 Mark II Time-lapse Movie clips shorter than they should be

[golf4motion]

Hi people, i need some advice about built-in "Time-lapse Movie" mode and long exposure settings.
It's about Canon R6 mark II.
I try to use built-in intervalometer but the calculation about movie time is wrong.
I'm making time-lapse at night sky. If i set exposure time 30 sec for every shot, interval between shots 32 sec, number of shots 250, takes about 2:12h recording time and calculation says at the end of shooting it should be 10 sec of time-lapse movie, but at the end it makes less than 10sec time-lapse movie.

Settings about movie is Full HD25.00 fps (PAL)

And its the same with built-in "Time-lapse Movie" mode in my 5d mk4. So its not problem in camera body.

[golf4motion · Accepted solution]

I find very good explanation of "interval" here and this helps to fix the problem:
https://youtu.be/xJC5lSzM1Ew?si=-VjBHRM6yssm2YqJ&t=549
So whats happen?
I turn on display to see what is happening between shots. The problem was if i use 30 seconds exposure time and i set interval 32 seconds somehow camera takes 33 seconds to close the shutter and save the image even when any noise reduction or other tools that can slow the process of saving is turned off. LOL, OK. 3 seconds of saving the image... And then when i set 32 second interval the first picture is saved, but the next one is skipped and camera just wait another 32 seconds doing nothing. And when this time finish camera start to take another picture. This is causing of losing a frame in the video. And the duration of the video gets completely different time. This is why the time of the finished video is shorter than the time showed in the menu.
Canon somehow must adjust this and not allow to use interval like 5 seconds for exposure like 30 seconds. It's pointless. Or just to fix the time of the movie at the end of capturing because of wrong interval. It's not easy to find out what is happening when in the menu is not even a alert when you put shorter interval for longer exposure, and nobody actually know how long it takes to save every long exposure frame.
So for 30 seconds long exposure frame you need at least 34 seconds interval for the movie timer to be correct.

[Waddizzle]

Just because the camera doesn’t work the way you seem to expect doesn’t mean it’s a bad thing or a bug. 

The built-in intervalometer blindly fires the shutter at the set period. It has no correlation with shutter speeds.  As you have discovered, you must allow for the time it takes to write to the memory card. If you had some noise reduction settings enabled, the write time would be equal to or exceed your shutter speed. 

That’s how any intervalometer works, including external ones. You must allow for both shutter speed and write time. 

[abulukas]

On a different note - could you estimate how long your battery would last for shooting? I'd like to do some time-lapse of northern lights in winter in Norway (which will drastically reduce shooting time), but was hoping to get an idea.