By Stephen Schweickart Print Article
We’ve given you a brief rundown of how to crush that depth of field, now let’s focus on one of those elements, the F-stop. Here’s a lot of words for you so be sure to take notes. On a lens, the F-stop number affects the size of the lens’ aperture by controlling the iris. Got it? No. OK here’s a simpler explanation. Imagine your eye is the lens and the pupil is the aperture, or size of the opening letting light into your eye. Your iris changes size in different situations to make sure your retinas don’t get fried from too much sunlight. On your eye, the iris controls itself automatically, but on a camera it’s controlled on a scale of numbers called the F-stop scale. And it’s very important to understand how the scale works in order to keep control over your image.
So let’s take a look at it, shall we? The scale starts at one and can go all the way up to 32 on a normal scale, with the amount of light decreasing as the number rises. So an f/2.0 will let in more light than an f/11. That part is pretty straight forward. Smaller numbers equal more light, which you know from our last depth of field video equals shallower depth of field. You may think the numbers on this scale are arbitrary, but they actually represent the ratio between the size of the aperture, and the focal length of the lens, which is the distance from the aperture to the film plane where the image is captured.
Using a DSLR to shoot gives you a lot of simple options for maximizing your aperture so you keep that depth of field nice and slim. First, put the camera on manual. If Terminator taught us anything it’s that you can’t trust machines and they may try to murder you in order to keep your unborn son from leading the rebellion in the near future. Not sure what that has to do with video, but nonetheless putting the camera on auto is the first step towards that future, and do you really want that?
Anyway, putting the camera to manual let’s you first control the f-stop, which for now we’ll assume you want as wide open as the lens will allow, letting in as much light as possible. From here, DSLRs have a handy dandy feature that let’s you select what ISO or sensitivity you want to shoot at. Now pay attention, this can get tricky. While the lower the F-stop the more light you get, the HIGHER the ISO the more light you get. So with the F-stop all the way open, you’ll likely need to lower the ISO to keep your shots from being blown out. It’s a simple process, but it will take some tweaking.
PHEW! That was a lot of information, but once you process all of that mess you’ll have a better understanding of f-stop, aperture, and iris, and ultimately will achieve ultimate control over your image.
Stephen Schweickart is the co-founder of VScreen. For more information on this topic, visit VScreen’s site at http://www.vscreen.com/video101.html.
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