Tyler Ginter • 180 Degree Shutter – Learn It, Live It, Love It

180 Degree Shutter – Learn It, Live It, Love It

I’ve received a lot of emails after posting my “How to Setup Your 7D”video tutorial asking what the 180 degree shutter rule is and why it’s so important. To be completely honest, before these Video DSLRs came around I didn’t really understand the principles of the 180 degree shutter rule myself. Video cameras I’ve used in the past always defaulted to a 180 degree shutter automatically so unless I went into the settings to change my shutter speed or frame rate, I was always good to go! However, this all changes withVideo DSLRs hitting the market because they have no preset shutter speeds to rely on and most of the manufacturers of these DSLRs don’t find this rule important enough to make it a primary feature. Therefore, I figured this would be a great opportunity to consolidate a few articles and resources on the web to answer this question once and for all.

I want to thank Jason Wingrove and Stu Maschwitz for breaking down the 180 degree shutter rule for me. Stu wrote an excellent blog about this topic last year when Reverie first came out describing why it is so critical to shoot at a 180 degree shutter!

During RedCentre Episode 25, Jason had a great discussion with Mike Seymour on shutters and keeping the film look. Check it out, it’s a great resource that dives further into the explanation I am about to give you.

I’m also seizing this opportunity to discuss the 360 degree shutter issue, as it’s one that needs airing out. Sure, it may be a creative choice for a filmmaker to use a greater-than-180-degree shutter, but when my mom sees the trailer for Collateral and asks me why it looks like video, we’re talking about a choice that sets back the progress of digital cinema. If you want your 24p HD to look like film, the film we know and love, stick to a 1/48 second shutter speed or faster. -Stu Maschwitz

With all that said, lets dive into why the 180 degree shutter rule is so important. With the rise of digital cinema it is critical to maintain the “film look” that we all love so much. We do this with shallow depth of field and low light from large sensors, interchangeable sharp/fast glass, Matte-Boxes, Follow Focus, Stedicam Rigs, Dollies and Jibs, 24P, color correction, vignettes/film grain, and the list goes on and on… However, one thing that is often overlooked and under appreciated is the 180 degree shutter speed rule.

To maintain the “film look,” first we need to examine how a film camera actually works. Take a few minutes to study the animation at the left. As you can see, a physical shutter on a film camera is basically half a circle. The opening defines the shutter angle. Just like ISO/ASA wasn’t a luxury to instantly adjust on the fly back in the day like it is today, neither was your shutter speed on film cameras. In order to change the shutter speed you had to physically remove the disc and replace it with another disc that had a different sized hole cut out. Likewise, to change the ASA on a film camera you would have to physically remove the film stock and swap it out with another roll. Aren’t we spoiled today?!?

Anyways, let’s quickly review… The physical shutter in a film camera has the shape of a half circle (as you can see in the animation). This is defined as a 180 degree shutter angle, makes perfect sense since a complete circle would be 360 degrees… In order for the film to feed through the gate while properly exposing each frame of film, the disc will have to rotate one complete revolution for every frame. Therefore if you are shooting 1fps, the frame would be exposed to the open part of the disc (allowing light to hit that specific frame of film) for only half of its complete revolution or in other words 1/2 shutter speed.During the other half of the disc revolution (while the closed half of the disc is blocking that frame of film) the next frame of film is being fed into the gate ready for its opportunity to be exposed. So, since we now understand that when shooting at 1fps, the shutter speed would be 1/2, then you basically just carry that math on! 24fps = 1/48, 25fps = 1/50, 30fps = 1/60, 60fps = 1/120, 120fps = 1/240 and so on…

Now very quickly you can see why the 180 degree rule can get dangerous pretty quick once you start filming with higher frame rates. When the 2/3″ Red Scarlet comes out with 120fps (150fps burst) then you will be cutting a HUGE amount of light shooting at shutter speeds up to 1/300th. The same goes for cameras like thePhantom that shoots well over 1000fps. In order to get the proper shutter speed you need to be shooting at least 1/2000 and pouring the light on the subject in order to maintain proper exposure during those extremely high shutter speeds.

So how exactly does the shutter speed affect your image? Well if you come from a photography background you don’t really need to read this explanation. However this is the true magic on the convergence of photo and video today! The same terminology and fundamentals are more important than ever in relation to aperture, ISO, and shutter speed. Therefore, what happens when you take a photo at a slow shutter speed – 1 second exposure? You get a lot of motion blur. What happens when you take a photo at a fast shutter speed – 1/8000 shutter speed? You stop motion.

Well the difference is when you’re dealing with digital cinema, filming at a greater than 180 degree shutter (which you should NEVER EVER do), allows each frame to contain too much motion blur which results in a “smeary” look… Besides, this is a look that would be mechanically impossible to achieve using a film camera since you need that extra time for the physical shutter to block each frame so the next frame can slide into place… Therefore, a greater than 180 degree rule looks unnatural so PLEASE don’t do it! I know, sometimes breaking this rule is so very tempting when it’s dark out, you have your aperture wide open, and are pushing your ISO to the max… You think to yourself, “I can open up my shutter speed a little more.” Just because the camera lets you do something doesn’t mean you should because before you know it, you’ll be shooting 24fps at 1/24th shutter… Don’t give into the temptation, stay strong because you’ll kick yourself in post when reviewing your footage wondering why your digital cinema looks like nasty smeary video. Yes, all rules are meant to be broken but this is one rule that if you don’t know exactly what you’re doing, you can really ruin your work.

So when is it alright to break the 180 degree rule? Well, if you are going after a certain effect like they used in“Saving Private Ryan” to get a staccato feeling then breaking the rule is acceptable. On the cameras they used for this film, they adjusted the standard half open/half closed disc with a disc that had a 90 degree opening for the majority of the film except for the high action combat scenes which were shot at a 45 degree shutter angle (to be more accurate, the shutters in these film cameras are electronically adjusted but the same fundamentals apply). Remember, those are LESS THAN 180 degree shutter angles so it’s alright. A 90 degree shutter angle would equate 1fps to 1/4 shutter speed or at 24fps they were technically shooting at a 1/96 shutter speed. That means they had to use a lot more light in their scenes to make this effect work…

What is an easy way to figure out how to convert from shutter speed to shutter angle and back again? Here is a very handy guide written up by Stuart English. My good friend Matt Jeppsen posted an excellent article titled “Shutter Speed vs. Shutter Angle” about this same topic which you can read about in more detail.

Now if you are using a Canon Video DSLR, then you will have to make a few minor modifications when choosing your shutter speed for your desired frame rate. If you are shooting at 24fps, the closest shutter speed you can select is 1/50th and if you are shooting at 60fps, the closest shutter speed you can select is 1/125th. This minor adjustment won’t affect your footage but it’s the principle that counts so Canon if you’re listening, please fix this in the future… Thanks!

Yeah I know, this is a very long blog about a very simple topic however if you are anything like me, you don’t just want to be told to do something without understanding why you should do it. This 180 degree shutter rule is something I never learned in college and there are tons of cinematographers out there who either don’t know about this rule or don’t obey it. Moreover, there are a lot of photographers starting to shoot video with these new Video DSLRs that need to start out on the right foot and use good habit and proper fundamentals!

UPDATE: Alain Pilon filmed this awesome visual example of 7 common shutter speeds captured at equivalent exposures and merged together in one clip. You can very easily see and understand the effect shutter speed has on water. The camera used was a 5DMKII which shoots at 30fps. Just look at how “smeary” the water looks at 1/30th (360 degree shutter) on the left hand side. Right next to it at 1/60th or 180 degree shutter the water is flowing naturally and it is pleasing to our eyes. For creative effects on the far right you can see that shutter speed begins to stop the motion of the water which gives a really cool look under certain conditions. Make sure you head over to Vimeo so you can watch it in HD. Thanks Alain for this great example!