Why Shutter Speed Matters With DSLR Video
I will be the first to admit that when I try to take on a new skill that I become completely obsessed with really understanding every aspect of it in order to do the best I can and use the new skill to its full potential. Such is the case with learning to shoot video with my Canon EOS 7D. Since the best video camera I had up until the 7D was a small Canon Vixia camcorder. While the Vixia can shoot 1080p video, the only settings are 24 fps or 60 fps. The only thing this meant to me was that if I shot action sequences at the faster frame rate, I could slow the sequence down better because there was more data to work with. Now that I am learning to shoot video on the 7D, I have ISO, Aperture, and Shutter Speed available. The big question is, how do these affect your image when shooting video.
ISO and Aperture
The good news is that two out of three aint bad. What I mean by this is that ISO and Aperture affect video exactly the same way that they affect stills. ISO will make the sensor more sensitive to light so just like stills, you can increase the light into the camera by increasing the ISO setting which, just like stills, will add digital noise to the image.
Just like still images, Aperture will open or close the lens’ aperture diaphragm to allow more or less light into the camera which will affect the depth of field.
So long as you already have a good handle on ISO and Aperture, the same principles apply to both stills and video so you already well on your way.
With stills, shutter speed is fairly simple to understand, a longer shutter will allow more light but may add motion blur while a fast shutter speed can freeze motion but cuts down on the amount of light entering the camera. The confusing part is how this affects video. Many new video DSLR owners simply think this affects only the light since the frames are already moving. The reality is that the shutter speed can have a significant impact on the video image and most of the articles on the internet are painfully difficult to understand.
The traditional standard for video is 24p (which is actually 23.976 frames per second) which is very pleasing to the eye and is pretty much the standard for camcorders and DSLR video recording (much more on this is available on Wikipedia).
To achieve a film look (which has just enough motion blur between frames to look natural without being “smeary”) you need to follow the 180 degree rule which, simply put, says that your shutter speed should be double the frame rate. This is one of those times when I want to say “don’t worry about what it means, just go with it” as the technical explanation is quite…well…technical. Tyler Ginter did a really good job explaining the technical side of this on his blog post 180 Degree Shutter – Learn It, Live It, Love It.
While I am not going to try to explain the whole 180 degree shutter concept, I will instead just jump into what it really means to you and your video.
Since we already know that when we are shooting stills with action, a slow shutter speed will have motion blur and a fast shutter speed will freeze action. When we translate this concept to video, a slow shutter speed will create a smeared look to the video. If the shutter is too fast there isn’t enough motion blur to smoothly transition from frame to frame causing a stuttering or staccato effect. If you have ever looked at something moving with a CRT monitor behind it you will know what this stuttering can look like. Sometimes, this can be used for creative effect like in the opening of Saving Private Ryan.
To see how this looks in actual video, I did this quick comparison of 24p video shot at both 1/50th (yes, I know 1/48 is double the 24fps but most cameras can’t do 1/48th shutter speed so we have to take the closest option which would be 1/50th) and 1/300th shutter speed.
What about exposure?
The issue with exposure is not when things are too dark as we can open up our aperture and increase our ISO (only to a certain point before we need additional lighting anyway) but when things are too bright, we only have a few options. If you are already at a small aperture and a low ISO and 1/50th of a second will result in an over exposure the temptation is to increase the shutter speed, but this is going to violate the 180 degree rule and cause the stuttering video.
The only way to knock the exposure down is with the use of a neutral density filter. The most versatile filter is a variable neutral density filter that allows you to dial in the amount of filtering. A good example of this is the Fader ND Mark II which is adjustable from 2 to 8 stops.
The real beauty of using a filter with this much versatility is that you can shoot at the relatively slow 1/50th of a second at wide open apertures to create a very short depth of field that just isn’t possible with regular camcorders. The ability easily create different depth of field shotsÂ is a key reason many filmmakers are jumping onto the DSLR video bandwagon.
The Exception to the Rule
Let’s face it, every good rule deserves a good reason to break it and the 180 degree shutter rule is no different. In fact, there is one really good reason to break it and that is when you are specifically shooting for video that will be shown in slow motion. If we use the basic rule of having a shutter speed that is double the frame rate, when we slow down the video we will end up with more blurry video. If you shoot at faster shutter speeds, when you slow the video down you will get cleaner looking video.
This actually brings up a major difference between shooting stills and video. With stills, our final output will be a still frame. Sure, you may use some panning and zooming in a slidehsow which may require cropping that isn’t very tight but lets not digress too much. With video, you really need to think ahead about how the video will be played back. Will the video be sped up, played at normal speed, or slowed down as this final product needs to be considered when choosing the shooting settings.
Hopefully this has helped make some sense out of the shutter speed issue with DSLRs. If you are just going to be shooting video for yourself, you may not care much about all this but if you are trying to really make your video look its absolute best, and most certainly you can achieve incredible results with the current video enabled DSLR’s, then this is one of those topics that you really need to get a handle on.