So you have your nice camcorder, EX1, EX3, AF100, F3 or whatever and it has a function called the shutter. This function may have different ways of being set, fractions of seconds or angle. What is it that the shutter does and what’s the difference between angle and fractions. Also why is it important to know what the frequency of the local mains electricity?
180 degree film shutter
Lets start by looking at the difference between shutter speed expressed in fractions of a second and shutter angle. Shutter angle comes from film camera days when the film cameras shutter was a simple spinning disc with one half of the disc cut away to allow the light to pass from the lens to the film. The other half of the disc would rotate around, blanking off the film so it could be advanced to the next frame. If you consider that a full circle is 360 degrees, then half of a full circle is 180 degrees. So for each frame cycle with a 180 degree shutter, light is allowed to pass from the lens to the film for half of the frame rate (180 being half of 360).
Taking a frame rate of 25 frames per second, each frame lasts 1/25th of a second. Half of that is 1/50th, so with a 180 degree shutter the exposure at 25P is 1/50th of a second. There is no difference in the way the shutter works, it is just a different way of expressing the shutter timing.
Film camera 90 degree shutter
If we take that and look at a different angle, this time 90 degrees we can see from the picture that this is now one quarter of a full circle (90 is one quarter of 360 degrees). So at 25 frames per second the exposure is one quarter of 1/25th which is 1/100th and so on.
So why use angle instead of a fraction of a second? Well here’s the thing. If you set you shutter speed to 1/50th, then no matter what your frame rate the shutter speed will be 1/50th. The Sony EX and XDCAM cameras can shoot at various frame rates (as can many other cameras). It is traditional when shooting progressive, trying to create a filmic look to mimic the way a film camera behaves, so for this you would use a shutter that is open for half of the frame rate, ie. 180 degrees. When you set the shutter speed using an angle, when you change the frame rate the shutter speed will also change. Set to 180 degrees it will always be half of the frame rate. So going from 25P to 30P will change the shutter speed from 1/50th to 1/60th. Which neatly brings me on to the next bit….
Why it’s important to know the local mains frequency.
We normally take it for-granted in our home countries, shooting at our home frame rates that the pictures will be OK. But if you travel to a country where the mains frequency no longer matches the cameras base frequency then you may experience problems with flickering or strobing pictures when shooting under artificial lighting. Sometimes you will see light and dark bands slowly rolling up and down the picture. This happens because if you take your camera, lets say set to PAL (50i/25P) to the USA, the US mains frequency of 60hz will drift in and out of sync with the camera from one frame to the next. As many artificial lights brighten and dim in sync with the mains electricity you can appreciate that for one frame the lights may have one brightness and then the next frame the brightness may be different. You will possibly experience problems when the mains frequency cannot be evenly divided by the cameras shutter speed. For example shooting 30P will give problems when the mains is 50Hz as 30 will not divide evenly into 50.
So how do you counter this? Well you need to change your shutter speed to an even fraction or even multiplier of the mains frequency. So shooting 30P in a 50hz country you can use: 1/50th, 1/100th, 1/200th etc (mains frequency, frequency multiplied by 2, multiplied by 3 etc). Note that when shooting 60i you can’t normally have a 1/50th shutter so your limited to 1/100th or higher. When shooting 25P or (50i) in a 60Hz country you should use 1/60th, 1/120th, 1/240th etc. For 24P (23.98) you will often have to use the shutter when using consumer or industrial lighting using the same shutter speeds as give above, dependant on the local mains frequency.
This is very helpful, thank you!
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This is great. I appreciate it! One question, I mainly shoot 24p and it is almost always narrative work. I currently use the EX1R. for a more “filmic” look you mentioned I should shoot at a shutter that is open for half of the frame rate. So Technically i should shoot at 1/48th of a second or set to 180degrees? This has been something that has confused me for a while. Everything you have ever written has been extremely helpful. Thanks in advance.
That’s correct, the norm would be 1/48th. But if you in the US 1/60th will match the local lighting or 1/50th in the EU and the difference is so small that the end result will look pretty much the same.
Thank you. So I finally had a chance to look through the shutter menu and I have all the options you have written about. I decided for a more “filmic” look to go with shutter angle and 180 degrees like you recommended.
I shot at 25p as requested by the editor as the footage was going to used on the web. Now I used no shutter and Im using a XDcam 700. While shooting all my exposures are as my normal shooting.
Then the editor mention that exposure was down about one stop. However when I replayed the footage back in the colour view finder when I was on location all seem to be fine. So the question is…is there a difference in exposure shooting in 25p and how do I compensate or has the editor got his wires crossed..
Cheers
There should be no difference between what you see in the viewfinder and what the camera records no matter what mode you shoot in. Normally when shooting 25P you would use a 1/50th shutter to keep the image sharp, but again the viewfinder should be WYSISWG.
Cheers Alistercha, That’s exactly what I knew to be the case ..But to be double sure I just had to ask. The only thing since asking that question, is that the master blacks may have been crushed just a bit and may have caused that problem. But other people use the camera of this production company they may have changed any of the setting so it’s a bit hard to track down if the blacks had been changed. All looked good in the view finder and on reply on a larger screen.
Just love it when a director trusts what a editor may say to trusting the person shooting…but I guess we all have the same problem out there…
Hi Alister. Thank you for your continued help. I recently have found that footage I have been shooting on my Sony F3 suffers from what I would call excessive motion blur. This happens both if I shoot with the shutter on or off. I’m not sure whether this is something you have found with that camera? I always shoot everything in 25p at 1/50th. I often find this to be a problem on a locked-off shot when someone walks from one side of the frame to the other. On close inspection, it also looks like it happens on sit-down interviews when the subject is particularly animated and moves his hands around or shakes his head a bit too fast. I always assumed that this had something to do with not having the shutter turned on.
Hmm, not sure what your seeing. I’ve shot all kinds of stuff including air shows and other fast moving objects with my F3′s and not seen any unusual motion blurring or softness. Anyone else seeing this??