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Shutter speeds


Michael Thames
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I hear that one should set the shutter speed to double that of the frame rate.  24 frames to 50..... 30 frames to 60 etc. 

 

My question, is this just mathematical theory, or can one see definite problems with the actual video if this ratio is not used.  I'm thinking if one were shooting outdoors and needed to lower the exposure and exhausted all other possibilities, would raising the shutter speed really be that bad?  

 

If this is so bad what might one look for in the footage, as far as a loss of image quality? 

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its more to abide by convention than to obtain a better image quality.  the motion blur you get at 2x your frame rate is appealing (due to this being considered the normality for motion picture, though a lot often break the rule).  Watch the first battle scene from saving private ryan and you'll see the effects of shooting with a very fast shutter.  watch apocalypto and see the results of a slow shutter.  

 

its a creative choice more than a technical one IMO

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Raising the shutter speed is really truly a last resort. If your shutter speed is too high or too low, the motion will look too "fast" and you will lose the cinematic feel. I once shot a whole event at 1/50th at 50fps and when I got home and viewed the file, everything just looked silly.

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My question, is this just mathematical theory, or can one see definite problems with the actual video if this ratio is not used.  

would raising the shutter speed really be that bad?  

 

It's not a mathematical theory cooked up by geeks. The origin of it is mechanical. This animation may explain more than a bunch of words. By all means read the Wikipedia entry, too. It does make sense, once you look into it.

 

Once you understand the principle behind the rule, you can start experimenting and breaking it, and to answer your second question, just try it yourself, make your own experiments, as well as examine those examples mentioned above.

 

FWIW, investing in an ND filter is not a bad idea, in case you haven't already. Sticking with the 180 degree shutter angle is generally not a bad idea, but feel free to experiment and come up with compromises that work for you.

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Sometimes raising the shutter speed helps:

 

  • If you're going to rotoscope or remove a greenscreen, or you're generally capturing a video element for compositing
  • If you wish to emphasise the violence of movement, such as in a fight scene or a chase, or for slow motion

In both these examples, the less blurry, more distinct images can assist you. In general though, 180 degrees is good

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would raising the shutter speed really be that bad?

 

Look at the result and decide for yourself.  Personally, I don't like it.  An interesting side effect of a high shutter speed:  Perceived resolution increases.  Since edges of things stay sharp and defined rather than blurred it just looks like there's "more" there.  However, that is not an organic image and is very mechanical/clinical to me.  

 

...And the only thing needed to control exposure in bright outdoor light is a modest collection of neutral density filters.  For mid-day sun, I like my ND rated @ 1.8; cuts down the incoming light enough that I can work my iris in the f2 range and adjust exposure with a bit of ISO play. 

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Thanks for all the very informative replies!!!   I forgot about how the increased shutter speed effects the jagged edges an makes things more jittery.  

 

I was recently in India and Thailand and had a huge problem with the electrical currents causing  a pulsation with the lights. In Thailand I shot in 30f and turned down the shutter to 30 as well and it seemed to help a little. At one point, it got so bad, I just turned it on automatic and said screw it. 

 

I'm doing a music video this weekend and we are shooting outside, I have a variable ND filter for my 24 to 105 lens, but just got a new 70 to 200 IS USM that I much prefer, but don't want to have to buy another ND filter this week as I shelled out money for a new computer.... so I got to make use with what I have.  

 

I'll just use the 24 to 105 outside I guess even though I love the other lens, but really in the end nobody will notice the difference in the lens except for me.... ha ha!  

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don't want to have to buy another ND filter this week

 

For what it's worth, I bought a single 1.8 ND and a collection of step up rings to adapt them all to my different lens thread sizes.  I typically hit the field with a collection of three primes, so it's pretty easy to swap.

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