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by Bart Arondson

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My camera is Canon 60D and I will be using it to shoot a short parkour video, that means:

  • a lot of motion, moving subjects, moving camera
  • focal length usually from 24 mm to 75 mm, but there will also be a scenes shot at 200 mm
  • a lot will be shot in 1080 at 24 fps (or should I use 25 fps or 30 fps ?)
  • some scenes will be shot in 720 at 60 fps

Accessories:

  • I do have a steadicam
  • I have got 1.8 lenses (24 f/1.8, 35 f/1.8, 50 f/1.8) so I can use low f-stops.

Questions:

  • What shutter speed should I use? I have read that it should be double the FPS. Why so? What if I break this rule?
  • When I use low shutter speeds (1/120) and I'm shooting during the day, I need f-stop at around f/12. Does this mean that my f/1.8 lens are useless in this case and I can use any bundle f/4 lenses instead?
  • Any tips on improving whatever I wrote above?
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1  
By the "intention" criterion suggested here, this is off-topic and should be migrated to avp.stackexchange.com –  mattdm Nov 19 '11 at 22:12

4 Answers 4

up vote 7 down vote accepted

The reason that many people will recommend to shoot at double your framerate is because then the 'shutter angle' is 180 degrees.

This is back from when film cameras were used. To cover the negatives whilst the next frame was 'wound on', a disc would spin, blocking the light as the negative moved. When the negative was in place, this disc would spin open again. Wikipedia has a good animation of this here.

The amount of covering the disc provides and the framerate give this 180 degrees that is as close as you get to a 'standard' in filmmaking. For further reading on this (or a better explanation!) I'd suggest looking over here.

As for a specific recommendation of shutter speed, it depends on the look you want. For example, some action films (using these as an example because they have lots of movement within the frame) will use a very fast shutter speed for sharp images, but being professional films they are still shooting at a framerate (or 23.976). Others will use the slowest they can get away with, and this will give them lots of motion blur within the shot. A good film that shows examples of both of these is The Bourne Identity.

TL;DR - It's a creative decision.

As for the problem with your F-stops, this is (unfortunately, because you have some real nice lenses) just something you're going to have to live with. Consider whether a slow shutter speed is absolutely necessary for these scenes. Using a faster one could allow you to use your f1.8. Also, depending on the camera you're shooting on, sometimes setting it to 'Auto ISO' can actually let the camera reduce the ISO below the minimum (100, normally) using some metadata hacks or something. (This may just be for stills, though!)

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This is by far the best answer to my question, only if you could tell us further: what shutter speeds (do you think) were used in The Bourne Identity? I know the movie from start to end so I wonder what did you mean. Do you think they used fast shutter speeds? What is a fast shutter speed when shooting a movie? Is 1/200 fast? 1/500 ? 1/2000 ? –  Richard Rodriguez Apr 21 '11 at 12:43
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Something to think about when you're picking a shutter speed is if you're shooting with practical light sources you need to try to sync with the mains AC frequency or you'll see strobing from the lights. In the US that means multiples of 1/60 and elsewhere 1/50. –  Ron Warholic Apr 21 '11 at 15:07
    
@RiMMER To be honest, I have no idea. I would consider that around 1/200 or 1/500 is fast enough to freeze most actions without motion blur, so sure, that would be 'fast' for me. As for what Doug Liman actually used.... your guess is as good as mine. –  nchpmn Apr 21 '11 at 23:51

What shutter speed should I use? I have read that it should be double the FPS. Why so? What if I break this rule?

The double the framerate suggestion comes from the film days when the shutter would close for the duration of the film advance and open to expose the next film cell.

Following this rule will produce natural looking footage as we're most used to seeing film shot with 1/48s exposures.

If you shoot 1/24s the footage will look a little fake. If you shoot faster speeds the motion will look jerky.

24 fps isn't really enough to create the illusion of motion so some motion blur is necessary in order to get smooth lookingfootage.

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Understanding the shutter angle as outlined in @Crashdown's answer is very important. The gist of it is that it essentially means you 'have to' eliminate one of the three controls you have over your exposure- shutter speed. Because when recording video if you want it to look like film you need to be very deliberate about what you choose for your shutter speed (it should be set at twice the framerate you've chosen to use, or as close as you can get) and then leave it there for the entire shoot unless you're changing it temporarily for a specific effect (such as the oft-cited 'stuttering' effect that was used during the action scenes in 'Saving Private Ryan').

As you've observed, this may mean that you won't be able to use your lenses wide open... or even 'somewhat' open... Turning down your ISO will only go so far on a bright day. After that if you want wide open apertures your only options are to turn down the light source (easier said than done if your light source is the sun) or put a Neutral Density (ND) filter in front of your lens in order to lessen the amount of light entering your camera externally.

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+1 for the ND filter which is a widely used DSLR accessoir for shooting with an open aperture. –  Simon A. Eugster Apr 21 '11 at 6:51

It is all about balance. Since you want lots of depth-of-field then you need a small aperture. To get a proper exposure you'll have to increase ISO and/or decrease shutter-speed.

Smooth motion is rendered by shutter-speeds close to the frame rate. So for 25 FPS, 1/30 is great and 1/15 is good. Slower shutter-speed are obviously not possible and faster ones create motion-blur gaps between frames which is why motion won't look so smooth.

Given your aperture requirement and the shutter-speed needed for smooth motion, you'll mostly be left with choosing the right ISO to get a proper exposure.

F/1.8 lenses mean they can open up to F/1.8 but they can also stop down. Most likely to F/22 but that depends on the model, I've seen limits between F/16 and F/64. So, no, those lenses are not useless.

The fact that you plan on shooting different format seems odd to me but I guess it may have to do with the way the videos are presented. If you are producing a single video stream for upload to Youtube or one of its clones, then sticking with one format will save you headaches in the editing phase.

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F-stop or ISO isn't a problem in my case at all. All I care about is shutter speed. I can adjust the rest properly and I have the lenses to be 'unlimited'. I just think 1/30 produces a blurry result, I don't know why I can't use for example 1/500 ? –  Richard Rodriguez Apr 20 '11 at 20:51
    
@Rimmer - Now, that you gave up on extensive DOF, you can open up but it will cost you ;) What need it to make sure your subjects is in focus and the wider your aperture, the harder it is, since your subjects are apparently moving. –  Itai Apr 20 '11 at 23:03
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@Rimmer - [Part 2] You can use 1/500s or even faster if you like but the motion will look more jerky. The effect of motion relies on our brain seeing the similarity between each frame and fusing them into a continuous motion. The faster the shutter-speed the larger the gap between images which makes it harder for the mind to interpolate continuous motion. –  Itai Apr 20 '11 at 23:06
    
OK well, I get this, so the ultimate question: are f/1.8 or f/2.8 lenses useful for shooting movies during the day with a lot of lightning, when I will be setting them to f/12 anyway? is there any difference between using f/1.8 lens set to f/12 and f/4 lens set to f/12 ? we're talking about perfect lightning conditions here, no dark scenes... –  Richard Rodriguez Apr 21 '11 at 0:00
    
Differences, yes, probably minor depending on the model. Between a 50mm F/1.8 and a 50mm F/2.8 at F/11 it can be nearly identical, but between a 50-200mm @ 50mm F/11 and 50mm F/1.8 @ F/11, differences are greater: Primes are often constructed of fewer elements, so they are less prone to flare. Other optical characteristics of the lens such as distortion and vignetting still apply at F/11, a little further F/13+ and you will hit the diffraction limit, reducing quality equally for all lenses. –  Itai Apr 21 '11 at 1:20

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