How Important is the 180 Degree Shutter Angle Rule?

Question

I do notice that the 180 degree shutter angle look better, and I try to achieve it whenever I could. However, when shooting in bright conditions, I could not achieve it without a variable ND filter, which is too expensive for me. Even the cheap ones are expensive, but they are pretty bad.

I am also occasionally forced to use 90 degree shutter angle as I’m always shooting at 60p (not knowing whether I’ll slow it down, which means I shoot at 1/120 instead of 1/60) and display at 30p, this means that even with a VND, I’ll still shoot between 180 and 90 shutter angle.

I’ve did some videos and no one ever notices what shutter angle I use (neither did I until I started learning more, and even now, I wouldn’t be able to tell without direct comparisons). I also shoot majority of my videos during the golden hour, which means half of my videos achieves the 180 shutter angle.

Is it still necessary for me to get a variable ND filter?

Answer 1

• The "180 shutter speed rule" you mention is only about setting your shutter speed at about double your camera's frame rate. It is not about actually shooting with a 180 shutter speed no matter what. So, if I shoot at 25 fps, I'll set my shutter speed at 50 (because I like my footage to look more natural -- without the strobe-like effect that comes with high shutter speeds). If I were to shoot slow motion though, I would opt to shoot at, say, 50fps and set my shutter speed at 100 (to get crisper slow motion footage), and so on and so forth.
• There is not relation between the "golden hour" and shutter speed. You can shoot during that time of day, or any time of day, with whatever shutter speed you pick, provided there is enough light.
• ND filters are really used to control depth of field when using a wide iris/aperture on your lens in bright conditions (like an f2.8 or wider in the middle of the day).
• This is a good, clear break down of shutter speed use in video:

Answer 2

The question is... is it?

Reading your question it is probably not for the projects you are making... let me explain why.

You do not mention at all the aperture if you really need a shallow DOF, and this depends also on the subject if you really have different planes that need to be blurred out. But this can be implicit, so let's think you actually use a wide aperture.

This DOF also is dependant on the focal length of the lens. A telephoto has more noticeable DOF than an angular lens, but you are also not mentioning it.

You do not mention the theme of the video. People dancing vs. a guy sitting on a chair smoking a pipe... Motion blur or the absence of it is different in both cases. Here is where you draw the line. See if the motion blur has meaning on your shot.

Your test subjects do not notice any difference.

Golden hour is relative, you probably do not need a filter at all, you do not mention if you need additional light or if it is backlighted, different scenarios.

If you know you shot at 1/120 and you would prefer shooting at 1/60 you do not need a variable ND filter, you simply need a 2x ND filter, which is cheaper. Or you can get a pack of ND filters by $15 bucks. Yes, you need a bit more time to change them, but returning to the question, if it were important to you you would spend a bit of cash on some of those.

Actually there are some scenarios where you actually need to shoot at faster shutter speed. Breaking the 180 degree shutter rule when stabilising footage

So, in reality, the question is, Is it important for this project?

Is it more important than DOF, than the focal length, than the composition, than the slight blur you get with a cheap ND filter or more important than saving some bucks?

You will then find the answer :o)

Answer 3

A 180º shutter isn't a hard, fast rule, as much as it's a benchmark. It's the most common setting in film, and you can think of it as a "normal" amount of motion blur for film and broadcast. It's the average setting, for what people are used to seeing on any random moment of film or TV, and as a camera operator, it's the simplest decision to make, when you're aiming to produce "normal" motion.

If you don't have an ND filter handy and you're shooting in bright conditions, you can use a higher framerate to darken your exposure, but it will cut the amount of blur in each frame by half. How this affects your output depends on how you intend to display it.

Let's say you record the footage with a 180º shutter at 60FPS, then plan to play it back on your timeline at 30FPS for broadcast, by displaying every frame you recorded, sequentially. This results in "slowmo" or "off-speed recording." In this case, the amount of blur feels natural, because it's exactly the same amount of blur an object would have if it were traveling half the speed.

On the other hand, let's say you don't want slowmo, you want the action to occur "realtime," so you use the "nearest frame" method of interpolation, which throws out every other frame. In this case, because each frame has half the amount of blur as "normal" footage played at 100% speed, it will look stutter-y, more crisp, or less smooth, by comparison. It will look more like the action movies which employ the technique for creative effect (Saving Private Ryan, 28 Days Later, e.g.)

But you can also blend the two frames together instead of throwing one out, and if you do it intelligently, you can re-create the natural blur you'd get by using an ND filter and a slower framerate. Optical Flow computes a vector analysis of each pixel's movement, and can re-create the way a frame should look with natural blur.

Older optical flow algorithms use a purely mathematical approach, which struggle in certain cases, can produce artifacts, and have difficulty with regularly-repeating patterns. Newer algorithms, like DaVinci Resolve's "Speed Warp" use machine learning based approaches, and can give better results, but are very computationally expensive, a cost which rises (literally) exponentially with resolution.

Some software will blend the two frames together for you automatically, by simply layering one frame over top of the other, with 50% opacity. This is easy for computers to do, and produces more smooth motion than you'd get otherwise, but when you pause a frame, you'll see a ghosted image, and discerning individuals will notice a difference on playback.

Of course, most Cinematographers and hardcore pixel peepers will tell you there's no substitute for a good ND filter, but ultimately the decision to get one is between you and your pocketbook. To make a truly informed decision, you should compare some of your own footage using the methods I mention, but be careful, or you'll become a pixel peeper, too.