Fixed Focal Length (Prime) Lenses & How to Choose the Right Lens for DSLR Video

Fixed Focal Length (Prime) Lenses & How to Choose the Right Lens for DSLR Video

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Today on Reel Rebel, Stephen Schweickart talks about finding the right lens with a fixed focal length and the folly of trying to use a built-in lens with a so-called 700x zoom.  So if you’re finally ready to get yourself a DSLR, it’s time to take a look at the types of lenses that you can get, what they’re used for, the advantages and disadvantages, and so on.  So let’s let Stephen take it away:

Overview of Fixed Focal Length Lenses

Why a Fixed Focal Length Lens?

Digital cameras that tout 700x zoom in their small built-in lenses aren’t telling you that the image will go out of focus after about 10x.

Advantages of a Fixed Lens

  • Closer resembles the focus of the human eye
  • Less glass to worry about, more light comes through, giving you awesome shallow depth of field
  • Image sharpness rules

Kinds of Fixed Lenses

You can go from single digits (fisheye) to 1000mm lenses.  The human eye is close to what a 22mm lens sees, so it’s best to start there.  The more you go under 22mm, the more of the image you see, but the image is also more distorted.

A low focal length equals super sharp images (sweet!), but you can’t really do much with the huge depth of field, so everything is in focus and you can’t really change that unless you put on another lens.

A higher millimeter lens will give you more shallow focus, but it becomes harder to keep the subject in focus if there’s a lot of movement.  High-millimeter lenses are designed for subjects that stay put, with little or no movement.  When you find a subject that works with a high-millimeter lens, though, the images can be spectacular, movie-like.

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Hi, I’m Stephen Schweickart from Vscreen where we make videos for companies, and today we’re going to talk about fixed lenses, and what focal length is best.

Go to any electronics store and pick up a handy cam. Even with that tiny little lens on there, they boast about their 700x digital zoom seemingly built for creepers trying to peep on Sorority houses. But when you zoom in digitally like that, the quality of the image drastically degrades and you’re stuck looking at a blocky mess when you get past the 10x mark. So that 700x is worth jack squat. Hopefully you’ve moved on from those lower end cams and have yourself a DSLR and a zoom lens by now. But if you really want top notch image quality and the ability to get that crisp Hollywood look, take the leap into the world of fixed focal length lenses.

With a fixed focal length lens you don’t get any kind of zoom out of it. You pick a lens, hook it on, and that’s the millimeter you get. Kind of like the human eye. You can’t zoom with these suckers and when they’re working properly, IE if you aren’t hammered, they deliver a pretty nice image to your brain, so why not try to recreate that in camera? The main advantage here is that fixed focal length lenses have less glass in them, so they let in more light to give you that ultra shallow depth of field we keep harping on about, and the image sharpness gets bumped up to the next level.

Lenses range from fisheye lenses down in the single digit millimeter range all the way up into the thousand millimeter telephoto range. To give you some perspective, the human eye sees about what a 22mm lens would see, and that’ll be our starting point. Moving down from there will get you into fisheye territory. The lower you go, the more of the scene you’ll see, and the more distorted your image will get. The low focal length makes it easy to keep your subject sharp, but you get a super deep depth of field. Everything is in focus and there’s not much you can do about it, except, ya know, put another lens on it.

Putting on a higher millimeter lens will really help crush that depth of field, but doing so can be tricky. The shallow focus really gives you that Hollywood polish, but only if you can keep your subject sharp. If you can’t manage that, you’re going to be stuck with a bunch of blobs moving around your shot and no one is going to want to look at that. Long lenses are more for low movement detail shots, not really sports or interviews, but the quality of the images you can produce are incredible.

Moving up to fixed focal length lenses is a huge step for beginner cinematographers since it basically means you’re stepping out of the amateur realm, putting your big boy pants on, and working like a pro. Do it right and you’ll be getting calls from LA in no time.


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