How does Aperture affect video?

When filming a video one of the common words you will hear is the word aperture. Most people care about aperture to get a very beautiful blurry background when shooting a subject. This blurry background is known as bokeh and it can either be good or bad. Typically the blurrier and creamier
it is when the background is out of focus, it’s called good bokeh. When setting up a shot, it’s part of the triangle of settings I keep mentioning. ISO, Shutter speed, and aperture. Aperture is a tricky setting, because it actually adjusts things in two ways. It changes the amount of light let into the sensor and the depth of field. Let’s talk about what happens when you adjust the aperture on your camera. When you open the aperture,
you are opening a diaphragm which lets more light into the sensor. You can picture a circle getting bigger the more you open the aperture. Opening the aperture is usually referred to as changing the f-stop (full stop). The lower the aperture (for example f1.8), the wider the opening is letting in more light. The higher the f-stop setting is, the smaller the opening, and it let’s in less light. So you might be asking why would I ever want to let in less light? Isn’t light KING?!?!

Well when you are adjusting the f-stop, you are also adjusting the depth of field. The lower the f-stop,the shorter distance of what is considered in focus. So at f1.8, the depth of field is considered shallow and only close objects will be in focus, and your background will be out of focus. This is how you produce good bokeh. If you raise your f-stop all the way to something like f/11, then things further away will be more in focus. If you wanted to capture your subject and clearly all the items in the background,
then this would be the setting that you want. The best way for me to describe it, is to picture an alligators mouth. If the mouth is barely open, the aperture is barely open, there’s barely any light getting in and the focal length is very far. If it opens up really wide, it lets alot of light in, and the focal length decreases. If this is hard to visualize, i’ll walk through some tests now showing how the aperture impacts your video.

Video Parameters:
Canon m50
f/2.0 to f/11
30 fps
iso 200 (800 at f/11)
15-45mm f/3.5 lens
22mm f/2.0 lens

Let’s go over what we saw from looking at the footage. As the f-stop was lower, we let more light in, and the focus was very shallow. I don’t know if you could tell, but with a shallow focus, it’s possible that someone’s
eyes can be in focus, but the ears or top of their head is not in focus. Sometimes this is what you want, depending on what shot you’re going for, but sometimes going too narrow isn’t what you want. Another thing you need to consider is all that light that’s being let in. If you were outside in the sun, f1.8 will usually blow out your image and overexpose it. This means you might have to crank your shutter speed very high to compensate, but if you are going for 2x the frame rate, this isn’t possible. You will have to find a way to make things darker by adding an ND filter (which i’ll cover in another video.) So just consider that when working at lower apertures. As I
increased the aperture towards f/11, you’ll notice it let in alot less light, and things in the background became more and more in focus. For a cooking show or maybe a group picture, I could easily see myself increase the aperture to make sure I don’t miss out on any details. However with less light being let in, i’ll most likely need to tweak the ISO which will inevitably add noise.

So to summarize again, aperture controls how much light is let in and the depth of field of a shot.If you are wanting to get that nice bokeh, then set your apeture on your shot, then accommodate the shutter, iso and lighting to accommodate the look you are going for. Getting this right takes practice, and setup, setting up this shot took me along time to get the look I was going for. Hopefully this was helpful and provided you with some insight onto how aperture works.

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