Slow motion 1080/25p HD on a 5D III and shutter speed for video on a DSLR?

A

analogs

Well-known member
I see people using the 720 at 50p on a 5D III then rescaling to 1080 at 25p so they can use slow motion but is the quality acceptable in professional standards??

Also can someone explain the relationship between using a higher shutter speed when recording footage for slow motion? I don't understand how it is necessary for slow motion. I thought shutter speed for filming affects the amount of light when shooting video since the shutter is open all the time for video or is it not??

Thanks
 
The shutter is not open all the time. You set it, however you want. The usual setting is called a "180º shutter" and it is open half the time (so, if you're shooting 25 fps, the "normal" shutter is 1/50s; if you're shooting 50 fps, the "normal" shutter is 1/100s). More about these issues here.
 
Thanks for the link Samuel. Makes more sense now!

Do you know if the same principle applies to how camcorder make auto adjustments when set in auto in regards to keeping the shutter speed at 180 degrees or are people using camcorder also better setting it at manual?
 
When you set it to auto, the camera does whatever the designer thought would be best. On pro cameras, it will usually be 180º (1/60s for 30fps video). On smartphones, it is 360º (1/30s for 30 fps video).
It is a very important setting, and shouldn't be set to auto anyway...
 
Thanks for clearing this up. I originally thought the shutter on a DSLR was the mirror lifting up but it seems to be an electronic shutter turning the sensor on or off? Is that right??
 
there are 3 things here:
* the mirror, which has to move up for the camera to take pictures (when it's down, no light can reach the sensor)
* the mechanical shutter: it's a black curtain thing behind the mirror, it opens and closes every time you take a still picture, it's always open when you're shooting video
* the electronic shutter: it's a logic process in the sensor, the time it takes between the "sensor on" and "sensor off" orders; superseded by the mechanical shutter when taking stills, but used for every frame when shooting video



this is what the mechanical shutter in the 5d3 looks like, when you disassemble the camera and take away the sensor (that black curtain thing is what opens and closes when you take a still):
MK3_Rear_3.jpg
 
When shooting stills, does the mechanical shutter have to open and close at the same accuracy as the shutter speed or just has to make sure its open and close when the electronic shutter is triggered on and off?

Very enlightening stuff!

Thanks Samuel.
 
for stills, the electronic shutter is open for a long time, the mechanical shutter opens and closes to determine exposure
for very fast shutter speeds (e.g. 1/500s), it doesn't ever get completely open; it's a double curtain, one goes up to open, the second one goes up to close, then both come back down at the same time without letting any light in; at fast shutter speeds, the second curtain starts to go up before the first one has reached the top
 
Samuel,

So is this right when shooting video at say 1/50 shutter speed.
- the mechanical shutter is open in video mode at all time
- when recording, in one second the electronic shutter turns on and off 50 times

Do I have this logic right?

Thanks.
 
Close, but not quite

When shooting video at 25 fps and 1/50 shutter speed:
- the mechanical shutter is open in video mode at all time
- when recording, in one second the electronic shutter turns on 25 times and off 25 times
(turn-on, wait 20ms, turn-off, wait 20ms, turn-on, wait 20ms, ... --> it's open exactly 50% of the time)

(if you set 25 fps and 1/60s shutter: turn-on, wait 17ms, turn-off, wait 23 ms, turn-on, wait 17 ms, ...)



edited: typo, I said "ns" instead of "ms", which is just plain stupid
 
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I am a little confused here.

If I am shooting 25 fps and 1/50 shutter speed. In one frame how many times does the electronic shutter open?

Is the shutter speed rating related to the frames or the seconds when it comes to video?
 
* for every frame, it opens once, then closes once

* they are independent (except shutter can't be open longer than the time between frames, if you're shooting 25 fps then 1/25s is the slowest shutter you can use without blending frames)
* but they are also related: as a general rule, you should set shutter speed at twice the fps (1/50s for 25 fps), but it's your choice, you can set 1/1000s and then the shutter will be open for 1 ms, then closed for 19ms, open for another ms, close for 19ms, etc

edit: oh, I see, I said "ns" instead of "ms" in the previous post; that was stupid...
 
The is a great question and a good thread but the original question hasn't yet been answered.

Let me ask another way: What shutter speed to use when shooting for slow motion.

Specifically, what is the best shutter speed to use when shooting 60fps intended for slow motion in a 24p production. Do you still use 1/125 or something else?

What about 30p for slow motion in 24p, or 48 for 24p, etc. etc?
 
Me: 180º rule, modified to avoid flicker from lights

So, on 50Hz land, shooting 60p, I set 1/100s. On 60Hz land, I would use 1/120s (or 1/125s if 120 is not available).
And similarly for other frame rates. For example, 30p, I would set 1/50s on 50Hz land and 1/60s on 60Hz land. 48p, I would set 1/100s on 50Hz land and 1/120s on 60Hz land.

I did post this link.
 
come on, it's not that difficult

frame rate: whatever you want, if you want just a bit of slow motion you can shoot 30p for 25p, if you can afford a phantom you can shoot 1000p for 24p
shutter: a multiple of the electricity rate, chosen so it is not far from twice the frame rate
 
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