Author Topic: Why can't I choose a shutter speed below 1/24 s ?  (Read 3981 times)

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Why can't I choose a shutter speed below 1/24 s ?
« on: May 18, 2014, 07:50:47 PM »
Hi, I wanted to try the advanced intervalometer to do a sunset timelapse, but it appears I'm not able to choose a slower shutter speed than 1/24s. It's the same in the Expo menu, and in manual mode. The only thing I found to set a custom shutter speed is to set it via the original canon menu, then the value will be correct in ML menus, which is quite annoying. It's the same with AETTR disabled, I can't figure out what's happening.

Thanks in advance for any help, as the sun is going down quickly here. :)

dmilligan

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Re: Why can't I choose a shutter speed below 1/24 s ?
« Reply #1 on: May 18, 2014, 10:45:50 PM »
Well, this is just how it is coded. The advanced intervalometer uses the same code as the expo menu, that's why they function the same way. These shutter speeds in the menu had to be hard coded to match the allowable rounded Canon shutter speeds, since mathematically there is no rhyme or reason to the displayed shutter speeds you can select, they are just rounded to nice even numbers (see here). I'm guessing that whoever coded it originally didn't feel like going all the way out to 30" and just stopped at 1/24 as this is the slowest possible shutter for video. No one has bothered to do the tedious work to fix all the rounded values and allow it to go all the way out to 30". Perhaps this will be done soon: http://www.magiclantern.fm/forum/index.php?topic=10648.0.

At least you can set some of the shutter speeds now directly from the advanced intervalometer menu, the way I used to have it coded, the only way you could set any of them was setting them from the Canon menu :p

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Re: Why can't I choose a shutter speed below 1/24 s ?
« Reply #2 on: May 19, 2014, 10:40:30 PM »
Oh I see, that make sense now. Great news, that'll be the perfect timelapse tool! By the way I tried the intervallometer yesterday to do day to night transition, but I wanted the stars to be there after so ETTR was not possible. With a shutter ramping, the only thing that went wrong was during the transition flicker appeared, because as the light was getting lower and lower, the camera would do 3 x 2s shots, then 3x2.5s, soflicker was visible. But your module was working freakin' great! Just need the longer exposure in ML menu now :p

dmilligan

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Re: Why can't I choose a shutter speed below 1/24 s ?
« Reply #3 on: May 20, 2014, 02:21:34 AM »
but I wanted the stars to be there after so ETTR was not possible.
I don't understand. ETTR works just fine even if there are stars ;). Here's a sequence I did with full day to full night and vice versa with ETTR:
.

during the transition flicker appeared, because as the light was getting lower and lower, the camera would do 3 x 2s shots, then 3x2.5s, soflicker was visible.
There are lots of options to easily deflicker footage.

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Re: Why can't I choose a shutter speed below 1/24 s ?
« Reply #4 on: May 22, 2014, 06:37:29 PM »
I don't understand. ETTR works just fine even if there are stars ;). Here's a sequence I did with full day to full night and vice versa with ETTR:
.

I thought ETTR would burn all the sky trying to bring the histogram to the right, I guess I'll experiment this when it's sunny. Those timelapse are amazing, could you describe briefly what ramping did you use ? Av or Tv ?

Also, didn't you just make the expo menu go all the way to 30" ? :D

Edit : amazing, will try it soon!

dmilligan

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Re: Why can't I choose a shutter speed below 1/24 s ?
« Reply #5 on: May 22, 2014, 07:02:14 PM »
I thought ETTR would burn all the sky trying to bring the histogram to the right, I guess I'll experiment this when it's sunny. Those timelapse are amazing, could you describe briefly what ramping did you use ? Av or Tv ?
Neither, I just used ETTR (I shot these before I made this module), so it's a combination of Tv and ISO. As long as you don't set the shadow SNR limit too high or use too large of a highlight ignore you should be fine. The idea behind ETTR is that you expose as far to the right as you can without clipping anything "important" (non-specular). I usually hit my expo limits well before the sky or anything important gets clipped anyway: 30" f/2.8 ISO1600 (the max I can do) still doesn't overexpose the sky at night. If you have a brighter sky, it's probably not a bad idea to make your exposure limits close to the "correct" exposure for that particular sky. Then once it gets fully dark, the exposure won't be changing (since you're at your expo limits) and you'll have less to deflicker.

The more difficult part is actually during the transition. Since ETTR is basically metering the next frame based on the current one, if the light changes enough between shots, you can get some overexposure (if the light is increasing, i.e. sunrise) you can actually see that happen in that video (note that it only happens in the sunrise shots, not the sunset). So for sunrises you need to set the ETTR exposure target a little lower, depending on your interval between shots. Those were my first sunrise sequences, so I did not realize this.

Also, didn't you just make the expo menu go all the way to 30" ? :D
Yep

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Re: Why can't I choose a shutter speed below 1/24 s ?
« Reply #6 on: May 24, 2014, 01:54:58 PM »
Neither, I just used ETTR
So if I understand it right, you set the interval to 35s from the beginning, even when it was still the day ? If so, is there a way to set interval to expo time + 5s ?