Canon® Lens Design
All right folks let's build the lands everyone grab your glass and we're gonna build the lens together wouldn't that be fun to do in here okay so let's let's just theoretically build the lens what do we want out of a lance ok what do you think would be important to have let's do some questions let's let's hear some feedback about what what do you think we should have in a land somebody pick up a microphone and let's just pipe pass the microphone down the line and just think of something that we need to part of the lens what's important in linz grab the mike what do you think is important in the lens the glass the glass okay let's hear some something else thie overall construction whatever it's cased in and needs to hold it all together is a good solid construction so doesn't fall apart yeah okay it's pass the mic down just what else what do you think is important to a lens designer what are we what are we trying to create netta holdup in weather okay maybe a whether whether ceiling on ...
there it might be important it's another issue might think about the overall quality of the lenses overall quality maybe the resolution of the lands okay so let's take a look at some of the things that are important great resolution we want a lens that's really sharp right isn't that what people look at how sharp is the lens but that's not the only thing about contrast, you wont have good contrast and lends you want your blacks, black and your whites white. You want the cut and you're going to see some photos where I'm going to show low contrast, they don't look very good. You want to lands that has really accurate color that represents the color that you're photographing. You don't want to put a purple ends in there and have everything purple. It's got a really refracted do the right things with the color distortions. We talked about distortions. You don't want things throwing things out of shape. It needs to be really project a smooth, straight lines. 00:01:51.21 --> 00:01:53. You would like to produce the smallest you don't. 00:01:53.68 --> 00:01:55. You want a huge nobody wants to carry around a huge 00:01:55.41 --> 00:01:57. lead, so let's design it as small and as compact as 00:01:57.96 --> 00:01:58. possible. 00:01:59.92 --> 00:02:01. We want to make it is lightweight is possible. Let's 00:02:01.88 --> 00:02:04. put the fewest number of lenses in there so that we 00:02:04.32 --> 00:02:06. could make this a lighter lens. But what if more lenses 00:02:06.99 --> 00:02:09. make it better quality? And then we get into a real 00:02:09.3 --> 00:02:11. debate around the round table about how we design 00:02:11.21 --> 00:02:11. our lands. We want it simple, the use. We also want it simple, the build because that's going to make it lower cost. Maybe we're going to make more money on our lines is if we bill the lens for twenty bucks and sell it for a thousand. And so these are just some of the ideas that go into how do we make a lens and what are some of the compromises? So let's go through some of these resolution resolving power to see fine detail, and so we need pretty high resolving power lenses these days, but you know what? They can get better. They can be better than they are today, but we don't need them because our sensors are limited to x number of mega pixels, whatever that happens to be. And so there will be different lenses that have different resolving power. And one of the things that has changed in the last twenty five years in my photography is that lenses have needed to get even better, because our digital sensors are better than the film that I shot when I started photography. Contrast ratio efficiency in transmitting light with minimal reflections. And so imagine there is an area of blackness, maybe one of these shadows and you have a lens that's bouncing light all around in there what's gonna happen is a little bit of light is going to hit that black area and it's gonna lighten it up. And so we want, as contrast, e of light coming through the lands and there's a little bit different when we get to actually printing our images and working with them. But through our lands, we want high contrast, we want our blacks, black and our whites white, as I've mentioned, you want light to come straight through the lens. You don't want it to be bouncing off these glasses and having this light hit areas that are not supposed to have light and that's what happens in getting low cost, low contrast lenses is that the light's bouncing around and it's not hitting to where it's supposed to hit 00:04:04.29 --> 00:04:06. flare issues? What if this person points are lands 00:04:06.89 --> 00:04:09. in a bright light source what's going to happen? This 00:04:09.29 --> 00:04:13. isn't good. We don't want this to be ruining our photographs, 00:04:13.59 --> 00:04:15. and this depends on the type of glass that we put 00:04:15.44 --> 00:04:17. in there, the codings that they have on in the shape 00:04:17.32 --> 00:04:18. of the glass. 00:04:20.15 --> 00:04:20. Diffraction. We talked a little bit about this before. So designing the lens, the aperture. Both of these have an impact on exactly what happens with that light. As we squeeze it through, maybe a small f sixteen opening. The materials that they use in the aperture can affect what type of scatter you're going to get. And what type of diffraction it's gonna look like. 00:04:44.05 --> 00:04:46. Chromatic aberration this is a big bugaboo for a lot 00:04:46.89 --> 00:04:49. of people and a lot of lenses have some fairly bad 00:04:49.56 --> 00:04:53. chromatic aberration a distortion when colors do not 00:04:53.21 --> 00:04:55. converge at the same point and this often happens 00:04:55.4 --> 00:04:58. when you're shooting a scene that has a very bright 00:04:58.09 --> 00:05:01. background with a solid object in front of it and 00:05:01.35 --> 00:05:03. so if we take a close look at this if you look really 00:05:03.98 --> 00:05:07. closely you'll notice a red line on the underneath 00:05:07.26 --> 00:05:10. side in kind of a bluish teal colored line on the 00:05:10.75 --> 00:05:14. upper side of those beams and this is light that is 00:05:14.21 --> 00:05:17. coming around those beams and it is not hitting the 00:05:17.52 --> 00:05:21. sensor in exactly the same spot now chromatic aberration 00:05:21.92 --> 00:05:26. just looks bad nobody likes this but it is correctable 00:05:26.7 --> 00:05:29. in software afterwards so for instance if you have 00:05:29.23 --> 00:05:31. light room you can go in there and they have little 00:05:31.6 --> 00:05:34. chromatic sliders that you can choose which color 00:05:34.23 --> 00:05:37. you want and how much you want to try to fix it and 00:05:37.13 --> 00:05:39. you can pretty much eliminate this but it's a little 00:05:39.82 --> 00:05:41. bit of a hassle in order to eliminate because sometimes 00:05:41.93 --> 00:05:44. you need to get a picture by picture to adjust the 00:05:44.77 --> 00:05:47. sliders to get rid of it and so it is correctable 00:05:47.56 --> 00:05:50. but it be preferable if our lenses did not have any 00:05:50.66 --> 00:05:51. chromatic aberration 00:05:53.25 --> 00:05:57. coma or co o matic aberration a variation in the magnification 00:05:57.86 --> 00:06:01. over the entrance pupil all right and so this is going 00:06:01.57 --> 00:06:04. to manifest itself, if you do, night time, star point 00:06:04.39 --> 00:06:07. photography. So I'm down at the very large array, 00:06:07.02 --> 00:06:10. shooting a nighttime shot with a very high quality 00:06:10.2 --> 00:06:13. lens that is excellent for this type of work. But 00:06:13.43 --> 00:06:17. it's not perfect. If you look at some of these stars, 00:06:17.36 --> 00:06:19. they kind of look like saturn because they've kind 00:06:19.56 --> 00:06:22. of blown out and they kind of look like a comment. 00:06:22.94 --> 00:06:27. And so this is a little bit of coma in this lens. 00:06:27.74 --> 00:06:30. I would prefer it didn't have it. It's a small problem. 00:06:31.18 --> 00:06:33. There really isn't another lens that doesn't much 00:06:33.4 --> 00:06:36. better job that works on my camera, so I live with 00:06:36.56 --> 00:06:39. it and there's. Not much in the way to correct that 00:06:39.64 --> 00:06:44. in post astigmatism, light rays of two perpendicular 00:06:44.44 --> 00:06:46. planes having different focus points. 00:06:49.15 --> 00:06:52. So, as light from one point passes through different 00:06:52.05 --> 00:06:54. parts of the lands, they don't meet up in the right 00:06:54.76 --> 00:06:57. spot. It's going to be a little bit of blurriness 00:06:58.25 --> 00:07:01. and that's, just something that is just going to blurring 00:07:01.22 --> 00:07:03. it's. Just not gonna look good. And so they try to 00:07:03.07 --> 00:07:05. correct for that with the right shape to the lenses. Distortion we talked a little bit about this before barrel distortion and pin cushion distortion it's on all of our lenses just fortunately for most of them it's not that bad of a problem some lenses are much worse than others and there's many websites and people who test lenses that'll tell you exactly how bad it is but this is something that could be corrected in post granted you are pushing pixels around which is affecting your image quality and you sometimes lose a little bit on the wide angle side because you have to push things in and then crop it a little bit because of the nature of barrel distortion and so we don't want distortion but we get in a little bit vignette this is a darkening of the corner both of these images show you darkened corners of the image it's preferable if you don't have this in many cases but a lot of photographers myself included will add it to a photograph just as an effect and if this seems somehow familiar let me share with you a couple of family photographs so these are a couple of the oldest photos in my family now on the right here we have amos and irving and urban is my great grandfather and amos is my great great grandfather and you'll notice that picture has vignette ing as does my great great great grandfather jesse and so the lenses did not let in this much light which is why we don't see the detail. We don't see the sharpness in the corners. In fact, if you remember those really old photographs, ah lot of them came in ovals, because the corners were so bad on those images there was. There was nothing to show their and so that's why they were oval and why we have squarish images that go all the way out to the corner. There, I'd mentioned focus breathing in the city section. And so when you focus with a movie camera, there is very little change in magnification. On I try and remember which lens I used for this example I don't recall it might be the hundred micro so this is a video so let's get this video started here now watch as I change the focus towards the far ground you'll notice that there's a magnification and framing change as I move this focusing back and forth when you're shooting movies you don't like this because you're trying to keep a really tight frame for still photographers it's not that big a deal it's a little bit of an issue when you're doing macro photography you change your focus and all of a sudden you need to move your tripod forward or backward it's preferable if a lens did not have focus breeding but they all due to some degree okay is the quality of the out of focus area and this is more a matter of personal opinion but there is a lot of consensus that people have about what's generally good and what's generally bad and so a good day okay we'll have a nice soft out of focus and a bad bo okay we'll kind of have a jittery focus it's more clumped up and it's not as smooth across remember when were talking about the aperture the shape of the aperture having a circular aperture will yield a highlight that looks like this good boake a highlight it's rounded whereas the bad guy okay, you start seeing the shape of the aperture in the lens and that's why we want are rounded apertures so there's a lot of stuff going on in the design and finally there's the construction issues how do we build this lens? What sort of parts do we use plastic parts for metal parts, metal parts or more expensive they're harder to work with but they last longer they're better saw the construction what size of focusing ring do we want to put on it how much is that gonna cost us? And so this has a lot of impact on the final product that you get so those are some of the things to think about what's going on behind the scenes in the design of your lands now toe actually build the lens you start with thes powdered compounds which they mix there's chemist that know how to mix exactly up to one hundred different ingredients in this big vat of chemicals are big it looks like a pile of dust is what it looks like sand and this can cost upwards of a thousand dollars per kilogram so this could be some very expensive materials that they've had to mine out of the earth and mix to get just right. And if you want to know how to make a lens this I'm not going to read through these but this is kind of the general process so that you need to go through in making the lands it's not just melting sand and suddenly you've got yourself a nice lands there's, a lot of things that go into the process. There's, some great videos on youtube. If you want to go on youtube and type in how lenses made or how cannon makes lenses, cannon has a nice three parts siri's on how they make lenses that settlement thirty minutes that show you going through this entire process. What it looks like, it's, very interesting. I'd love to go to the factory and see that then we needed to figure out, well, how many elements are we gonna have in there? What sort of material are we using? What's, the order, and how are these lenses all grouped? Because we can make any particular lands in a million different ways, according to what we want to do with these kind of factors in here.