Optics

Module 1 Topic 4 Lens Optics & Seeing

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• published: 18 Oct 2016
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0:09 Let's start talking about some of the more technical aspects 0:12 of photography. 0:13 The reason that these technical aspects are 0:15 important is I don't think you can fully have an appreciation 0:18 of what you're trying to do as a photographer unless you 0:22 really understand as much of photography as you need to. 0:26 There's an interesting comparison here. 0:27 Think about it in terms of language. 0:30 Technique is like vocabulary. 0:32 The more technique you have, the more you understand 0:35 different ways of working with photography, the greater your 0:38 vocabulary for expression, the more you can explore through 0:41 photography, and ultimately, the better you will be taking 0:44 the kinds of images that you want to take. 0:47 We're going to start talking about lenses and optics 0:49 because the lens is how photography draws our image. 0:54 Rather than us drawing it with out hands, we need to use a 0:57 lens in order to do that, so there's lots of things that we 1:00 need to be able to consider as a way of 1:02 dealing with that lens. 1:04 In fact, pre photography, lenses already existed in 1:08 different devices called camera obscuras or even camera 1:12 lucidas, where the lens would project an image onto a sheet 1:17 or onto the back of a tent or onto a little box, and the 1:21 artist would draw the outline of what they were seeing 1:23 through that lens. 1:25 So that relationship with optics and drawing is even 1:28 older than photography. 1:29 But let's have a look at what lens might look like. 1:33 Here's the lens here, here's the inside of the lens, and 1:36 down here, we've got our sensor plane, or where the 1:39 light's being captured. 1:40 Now, the thing about lenses is that they bend light, and 1:44 light needs to be bent so we can focus on different picture 1:48 planes as we're looking at the thing that we want to 1:51 photograph. 1:52 So light will come through, and it will bend itself to a 1:59 very particular point right down here. 2:03 This is obviously one point of focus, and that becomes a 2:07 critical area of focus from what it is that the plane is 2:10 being captured out here. 2:12 So this idea then also translates to the type of lens 2:17 that we're using, and that distance from there to there 2:22 becomes our focal length. 2:26 So in this case, maybe this is a 35 millimetre lens, so that 2:31 distance from here to here is 35 millimetres. 2:37 Now, there's something else that the human eye and a lens 2:40 do differently. 2:41 As I focus on a particular point, my sight is quite 2:45 small, and the acuity and spatial awareness that I have, 2:48 and my peripheral vision, they're all defined on that 2:51 one particular point. 2:53 And in order for me to look at, or focus, on other areas, 2:56 I simply just need to move my eyes around. 2:59 We don't notice this because we do it so quickly. 3:01 A lens, however, has a different set of parameters in 3:04 the way that it sees things. 3:06 It can see the whole perspective, or the whole 3:08 peripheral of what it's looking at, with the same 3:11 level of acuity and spatial awareness. 3:15 If you look at my face, for example, now I'm in focus. 3:19 As we shift the lens out, my face becomes out of focus, and 3:24 then it comes back in focus. 3:26 That's a particular thing that a lens is able to do, and it 3:29 makes for a really interesting way of drawing our image using 3:32 these lenses. 3:34 American photographer Stephen Shore calls this the mental 3:37 level, the fact that when you're looking at a 3:39 photographic image, the image is flat, but your eyes 3:43 perceive depth, and you move around the image in the same 3:46 way that you would move around, for 3:48 example, a normal scene. 3:50 Consider this image here, Cappadocia. 3:52 There are three elements in this plane, or three receding 3:55 levels of depth, but because the frontal object, the house, 3:59 is so pronounced, that becomes the thing that sits forward. 4:03 And yet the background, the mountain ranges in the 4:06 distance and the sky, look like they're receding even 4:10 though they're all on the same level of flatness. 4:13 The other wonderful thing about lenses is that we can 4:16 use different types of lenses, and the longer the lens, the 4:19 bigger the subject appears in that frame. 4:22 So this is a 35 mil lens. 4:24 If I double that, I've got a 70 mil lens, which means that 4:29 any subject that was here in 35 mil lens is going to be 4:33 twice that size for a 70 mil lens. 4:37 And there are three images that will 4:38 4:40 4:44 4:47 4:50 4:54 4:57 5:00 5:03 5:05 5:07 5:09 5:10 5:13 5:18 5:21 5:25 5:27 5:29 5:31 5:35 5:39 5:42 5:47 5:50 5:51