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The Basics of Lenses Explained - Lenses for Filmmakers

Introduction

Today, we’re talking about lenses!  So lets not waste any time and jump right into it!

All About Lenses

The following text has been transcribed for optimal reading

Most of us know them as that expensive thing in front of your also very expensive camera. (hold up cam and lens)  But what do they do, why are there so many different options, and more importantly, which lens is right for me? There’s a lot of questions but we’re going to be going over some of the basics here today.  But first, disclaimer, lenses are complicated, so this isn't a video containing everything you need to know. This is an introduction to lenses if you want a place to start.

Let’s start simple.  What is a lens and why do you need it.  Well let’s take the lens off the camera and see what happens.  We get a white blank white nothingness. Right now light is hitting our camera’s sensor, but there’s really nothing else going on.  The job of the lens is to focus the light so that when it hits the sensor of your camera, there’s actually a discernible image. This is exactly what the lens of your own eye does, focusing light which then hits the retina in the back of your eyeball so that you can make out the shape of the expensive camera you just bought.  

So why won’t just any lens work for the scene you’re shooting?  Why are there so many options and what’s the difference? We’re going to cover 3 main variations.  


Focal length, aperture, and Zoom vs Prime lenses.

So let's start out with...

Focal Length

Focal length by definition refers to the distance between the center of the lens and it’s focus.  But for our purposes, it refers to how wide or how zoomed in a it makes your image look.  A wider lens like 24mm will look like this, showing a very wide amount of area for you to look at.  While a 200mm lens positioned in the same place will look like this. Allowing you to see WAY less of the scenery and making your subject appear much bigger in the frame by comparison.  

There are a crazy number of different focal lengths that you can potentially have at your disposal, and they each give a slightly different viewing characteristic.  In addition to being wider, or more zoomed in, there’s also a few other characteristics about focal length that you should be aware of. For starters, the wider your lens, the more distorted your image will become.  If i’m too close to my wide angle lens here, you can actually start to see it make a real mess of my face, making it look rounder and more alien than for example if I got as close as I could to my 200mm lens.  The difference becomes very apparent, and shows you just how the focal length actually changes the way your subjects face actually looks structurally. Here we try to show you a quick set of snapshots to see how a person’s face visually changes when you film at different focal lengths.

But the reason that it changes the way the face looks is because of how each lens displays the distance between objects at different distances.  We notice it right off the bat with faces because we’re so used to as people, looking at faces.  But when we take this object in the distance here filmed on a 24mm lens, and then change the lens out for a 200mm lens, we can see that it now looks like the object is much closer.  This is because wider lenses make things look farther apart, whereas longer lenses compress the distance between objects, making them look closer together.

So what does that mean for you?  How does that influence what lens you choose?  Well it means that if you want to want to really exaggerate how far away something is, use a wide angle lens.  

But the opposite is true too.  If you want to cheat and make it look like something is closer than it really is, then a longer lens is your way to go.  This is really useful for showing stunts where you want to keep your actors safe.  That way you can make it look like your subject is really close to a dangerous situation when they’re really a safe distance away.  

But unless you’re shooting something incredibly stylistic, you probably don’t want to be shooting all the time at these two extremes.  All throughout the middle in between these ranges are a variety of focal lengths that can serve your purposes for different occasions. Keep in mind the characteristics that you saw at each of the extremes, and as you leave those extremes and go closer to the middle zone, you’ll see those effects diminish, all the way up until you reach about 50mm.  Why a 50mm lens? It’s less about the lens, and more about your own human eye. It’s been said that shooting through a 50mm lens gives about the same experience to viewing with a human eye.

Aperture

So when you hear people talking about lenses, you’ve probably heard them talking a bunch of numbers.  And if they’re talking 24mm, 35, 50, 200mm, you probably understand those a bit better now. But there’s other numbers that people refer to often when they talk about lenses.  And that’s probably either a t-stop number or an f-stop number, but both of those have to do with the lenses aperture.

Let me say that, yes, t-stop and f-stop are different terms, and they mean slightly different things.  But for the purposes of this video, we’re just going to use the term f-stop as a starting point, and maybe one day in the future we’ll go over the difference in-depth.  

Basically, the f-stop refers to the size of the opening of the lens.  This number can change because lenses have aperture blades that can artificially make the hole larger or smaller.  If the lens itself is marketed with a particular f-stop number, that means that’s the widest open the lens is capable of being.  When you’re actually shooting with it, you might see an f-stop number on your camera display, which will refer to how wide open the lens is at that particular time.  The lower the number, like for example with this cinema lens, the wider the opening. The larger the f-stop number, the smaller the opening.

Cool, so...why does any of that matter.  Well just like with focal length, changes to your aperture parameter will actually drastically change the look of your footage.  When you raise and lower an f-stop number, there's a few different things that happen, but the first is that your image will get either brighter or darker.  If you close it down to a larger f-stop number, and make the hole smaller, you’ll probably be able to understand that this means less light can get through the smaller hole and your image is darker.  Conversely, if you open up your lens wider, to a lower f-stop number, your image gets brighter.

Might sound self explanatory, but that’s not the only thing that changes.  When you close down your f stop to a larger number and make the hole smaller, which actually makes it so that more and more of your image is in focus.  More specifically, it gives you a wider depth of field. This wider depth of field will allow you to have objects that are further apart both sharp and relatively in focus at the same time.  This is great if you want to capture an image where you can distinguish multiple different elements of the scene at different depths.

But the opposite happens if you open up your aperture.  The wider open you get, the narrower your focal range will get until you get a very fine razor thin area that’s able to be in focus at any given time.  You might notice this as having some of the qualities of film that you’ve come to appreciate. Having an out of focus background and a very in-focus subject.  And the more out of focus the background, the more your subject can pop out by comparison.

Typically a rule of thumb is that the lower the possible f-stop on the lens, the more expensive the lens.  That’s because as you create a lens with a wider aperture able to produce a shallower depth of field, it gets exponentially harder to get that next little distance.  That’s why a canon nifty 50mm f1.8 is priced at $100, while their f1.4 model is $350.  And finally the Canon 50mm f1.2 model is $1300. Yikes. There’s other factors that also come into play but it gives you a bit of a general idea.  But once you get to that incredibly slick f1.2 shallow depth of field, your images will be instantly better right? No

Shallower depth of field can actually come with some tough territory.  For filmmakers, if you open your lens up completely and have a really fine shallow depth of field, you might have trouble keeping focus on your subject if they’re moving around.  Not to mention that it might be challenging to keep your scene from blowing out if you open up your lens as wide as it goes.

In the end, it’s about knowing how aperture works so that you’ll be able to utilize it properly when you’re actually filming your next subject, landscape, or whatever you’re doing.  

And finally...


Prime Lenses vs Zoom Lenses

A prime lens just refers to a lens that’s fixed at only one focal length.  Besides that it retains all the other qualities of lenses that we’ve gone over.  A few common focal length examples are 24, 35, and 50, 85 and 135 just to name a few.

On the other side, a zoom lens simply refers to a lens which is able to change between a range of different focal lengths within the same lens body.  You're able to choose any specific focal length in between the maximum and minimum range of the lens' capabilities.   

Okay, so here’s the next question.  If it’s really useful to have a lot of focal lengths at your disposal, and it’s helpful to have your lens open up super wide, why wouldn’t you just always have a zoom lens?  Say one that goes from 30mm all the way up to 300mm, that can have a really low f-stop at each of those focal lengths?

Well the reason?  Because it’s borderline impossible, and the few lenses that can actually pull that off have a HUGE price tag attached to them.  Because it’s a feat of visual engineering that’s insanely hard to pull off.

Even a lens like this, the Canon 70-200mm at f2.8 will cost you around $2000 depending on which model and where you get it from.   And even then you’re not getting the ability to see any sort of medium to wide angle. So if you’re not literally made of money, prime lenses are probably something you should look at.

What’s the benefit?  You can have a high quality beautiful lens, with a low f-stop, for a lower price.  For this rokinon cine prime lens, that low f-stop is T-1.5. And the price tag is significantly more manageable.

On top of that, when you think about some of the movies you’ve watched recently, how often are they zooming in and out with the lens, as opposed to actually physically pushing closer with the camera itself.  The truth is that unless you’re filming the next re-boot of the office, you’re not going to be doing a lot of zooming in your filming career. A cheaper, higher quality option, it to actually use prime lenses and whenever you need to frame your subject differently, either move the camera, or change the lens to a different focal length.  

But some of you might say, wait, zoom lenses are actually essential to what I do.  Like if you’re a wedding filmmaker and you need to be able to adjust your framing during the ceremony in an instant, where you don’t have the luxury of taking the time to be switching out your lens.  

Yeah! That’s totally true.  The point isn’t to say that prime lenses are better than zooms or that zoom lenses are better than primes, but to show that they’re different, they’re both available, and they each serve their different pros and cons.  

The goal is to get you to know even more about how lenses work and what some of the benefits of each situation are so that you’re more prepared as you move along your path of filmmaking.  

Guys I hope you found this brief crash course on lenses helpful.  Filmmaking is such a big topic and there’s so many more things to consider when trying to up your game as a video creator.   So, feel free to check out all of our filmmaking tutorials right here at motionarray.com. But guys that’s it for me. Thanks so much for watching, and I can’t wait to see you, in the next video!

Well, that concludes this tutorial. I hope you found it helpful, if you did, please give us a thumbs up and if you’d like to see more tutorials, we’ve got lots of other Premiere Pro TutorialsAfter Effects tutorials, and filmmaking tutorials for you to check out!

Thanks for watching and see you in the next video.

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