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Lens Quality

So we've gone through our angle view and our apertures and depth of field, and I want to talk a little bit about lens quality, alright. So there's a number of ways to describe the quality of different lenses, and one of them is resolution; how much resolving power do we have to see that fine detail in the images, and there are some lenses that have greater resolving power than others. One of the things that I have noticed about many of the manufacturers that have been making lenses for a long time, like Nikon and Canon, is that they are coming out with new lenses that do exactly the same thing that their old lenses do, but they do it better quality. And that is because the quality of the sensors has gotten higher in recent years, and we need to have lens quality that matches the sensor quality in the cameras. And so this is not a number that you look at when you go buy lenses. You can look at reviews, you can look at tests about this, but this is just something to know, that different ...

lenses have slightly different resolving power, and there are places where you can go online and see exact technical results between them. Lenses are prone to flare when they have bright lights shining in front of them, and so you can see examples of flare in these two images, and this can be prevented with a lens hood. We'll talk more about that, particularly in the gadget section, but all lenses are likely to have some flare. Some are much worse than others. It really depends on the lens. Typically, the more elements and complex the design, usually the worse the flare, but it really depends on how well they've designed that particular lens. Diffraction is another problem. We talked about this when we stop our aperture down, and so this is the graphic that goes along with it. When we stop that aperture down, and it forces light through that small opening, the light scatters a little bit and becomes less sharp, 'cause it's not directed to going exactly where it needs to go, and so they are bending as they go by that very small aperture. The smaller that aperture, the more of those light, the higher percentage of those light rays are hitting that edge and potentially causing a problem on it, and so that's called diffraction, and that'll happen at a different point, depending on the lens and the sensor you're using; but, usually somewhere around f 11 to 16, you're gonna start getting diffraction problems with most lenses. Another challenge is chromatic aberration. This is a distortion when colors do not converge at the same point. Chromatic Aberration. Chroma: color, aberration: ghosting. So, a color ghosting. And so, as you can see in this example here, the bright light, as it comes around the beams of this window here, kind of change color into this cyan and red-ish color, and so you'll see this in areas that have highly backlit situations, and this is something that can be fixed in post. You can go into Lightroom, for instance, and you can describe what type of chromic aberration you want to fix, and you can drag a little slider back and forth to correct through these problems. A lot of cameras will have chromatic aberration fixes built into the software on their cameras, so that, right as you shoot, it fixes this problem, this problem that is occurring in their lenses. And so, this happens, and they're trying to correct through this as much as possible on the newer lenses, but it still happens from time to time with these bright, back-lit situations. Another problem is distortion, and we talked about this earlier, but, in many cases, it'll be classified as Barrel Distortion or Pin Cushion Distortion; whether it's kinda puckering out or puckering in, and all lenses have some sort of Barrel Distortion or Pin Cushion Distortion. Some are close to what-- they end up giving a rating of zero, or zero point one; it's only a little bit off. And so, each lens has a slightly different formula as to how it's incorrect, and there is a lot of software; for instance, Adobe Lightroom, the program that I'm most familiar with, which is why I keep quoting it, has a fix that they can go in, they can test a lens, they can see how much it's off, because, sometimes, it might be a little bit more off on the sides than it is on the top, and there are corrections that can be done in post to fix all these bent lines up later, but it's best if you can just shoot it straight out of the camera and have it as good as possible. Another little thing to think about is vignetting, which is a darkening of the corners. And so, you can see in the top shot, very clear, it gets darker as we get off to the corners. Now, the shot below has vignetting, but I don't really have a problem with it. I kinda like that look, and so fact of the matter is, and this is just a purely personal style of mine, I add vignetting to some of my photographs. I like the darkening of the corners, 'cause what happens is your eye tends to go to the lightest area of the frame and, if you wanna draw the eye away from the corner, and more towards something else in the frame, you would have a little bit of darkening to the corners, so it's a very common fix, or not really a fix, but a little added touch, that a lot of photographers will put on their photographs. This was a problem in the early days of television. Remember the early televisions? They didn't really have corners on those TVs, and that's because those early lenses had so much vignetting, they didn't even want to show you the corners. In fact, there are some TV sets that had a circular image in there, because their lenses were so terrible, they had this horrible vignetting, that you just got this round image, and that's one of the things that's changed in TVs since when I was a kid. They always used to have just a little bit of corners; they never went to the corner, 'cause that was one of the worst places when it comes to sharpness and brightness. And this is something that you'll notice more on really fast lenses, like at 50 millimeter, one point four lens. It'll typically have more vignetting than a 51 eight lens, and so, any lens that really is very fast in aperture, you're gonna get a bit more vignetting in most cases. Bokeh. Bokeh is the quality of the out of focus area. It's not just how much it's out of focus, but it's very, very closely related to the aperture setting on your lens, but it has more to do with the size and the shape of the aperture, and exactly the formula of lenses, and how it renders the background out of focus. And so, this one on the right was shot with a different lens that does not have as good a bokeh, and a lot of the terminology that we'll use is it has a jittery background. Can you see that kind of repetitive pattern in the background? That is just naturally rendered by that lens, which is not as smooth, and so we'll talk about a smoothy, creamy, out of focus background. And, if you'll notice some of the highlights, they're just a little bit more jumpy in there, in how quickly they change from light to dark, and it's just a smoother, out of focus area, and the better quality lenses will have this better quality of out of focus background, and it's it's not the first thing you look for in a lens, but it's just kind of one of those, well, it's either really good, or it's maybe not so good in that particular category. And so these are other optical challenges that you are gonna wanna look for when you're comparing one lens against the other lens. A final thing is the construction. Some inexpensive lenses will use plastic mounts, because it's cheaper to make, and they can sell the lens for a lot less money. It's a little bit lighter, as well. The focus ring can be very, very small on some of the inexpensive lenses, and a serious photographer might want to be able to grab that focusing ring, and it's nice to have a nice, wide, rubberized focusing ring to turn on there, and so there's a lot of other construction within the lens that we can't even see that is different from a high-end lens and a low-end lens, and so just the numbers on the outside, the focal length, and the maximum aperture, does not tell us the complete story of that lens. It's just kinda the headline on the cover of the book, and there's a lot of other things going on. Now, can you shoot pictures with a basic construction lens? Absolutely. Sure thing. They can render very sharp images. How long is it gonna last? How much do you like working with it? There's a lot of other issues to be concerned with that you wanna think about how does it fit in with what you do. And so, some other things to think about when choosing lenses. The optical hierarchy is, what are the best lenses out there? Typically, the best lenses out there are gonna be your professional prime lenses, like a 200 millimeter f/2 lens. It's not a zoom lens; it's a prime lens, and it's one of their top-quality lenses. Kinda the next up on what's a good quality lens is just a prime lens that has a single focal length, like a 50 millimeter, 35 millimeter one point four. Those are gonna be really good optical lenses. After them is probably gonna be your professional zoom lenses. So, your 24 to 70 two point eight. Really good lens, but probably not as good as the 35, nor as good as the 200 in pure optical quality. After that, we have our standard zooms. These are our kit lens that we often get with cameras as a packaged outfit, and so they're they're a little bit down on the list. Below them is our superzooms. And so, when you want a lens to do everything, like 18 to 200, that is going to compromise the optical quality a little bit. Now, the real question is, does it give you images that is below the quality that you want in your photographs, because this might be perfectly fine for a lot of people who want basic photography, and they want one convenient lens. And so, sometimes, this is the lens I recommend. It might be the lowest on the hierarchy, but it fits the needs. Now, the other little thing, and we'll talk a little more about this, is the teleconverters. When you add teleconverters, it seems to take any lens and drop it down one level on the hierarchy. So, people will often ask questions. "Well, can I put this teleconverter on my superzoom?" I say, please don't do that. That's gonna make it terrible. "Can I put it on my standard zoom?" I really wouldn't recommend it. "Can I put it on my professional zoom lens?" On some lenses, it can be okay. Some lenses, the very best of these zooms, then you're gonna be okay. "How about on a prime lens?" Yeah, that's probably gonna be pretty good. And on your 200 f/2, that's where they were designed to go on, and there you're gonna get good results. Not as good as just a straight lens, and so, you stick a teleconverter on this, it's not the same thing as a 300 in image quality. It's close, but not quite the same. Alright, and that brings to a close one of my favorite sections in this whole wonderful world of photography, is the lens. So let's catch up and see if there's a catch-all of anything anything in lenses that we can answer. I love this section, too, John, because a lot of us, when we start, are just thinking about the body, what body should we get, but then, when you go into understanding all the different variables of what the lens does, you really start to understand what the potential is with all those different lenses. So, let me ask a question from the Internet, and let me know if you've got any in the studio. This question is from Steph B. "If you want to intentionally achieve lens flare or sun flare, what aperture is best?" Ooh, for lens flare or sun flare. I don't know that changing the aperture is gonna change the lens flare that much. I haven't really done an experiment with that, but I would think that opening the lens up might cause more of a problem with lens flare, but there is occasion where, by closing the aperture down, light will bounce off the aperture and the back of the aperture, and that could cause lens flare, 'cause there's all sorts of things that are moving within the lens that might cause lens flare, and so it would depend on the lens. Kind of interesting, I don't know. I'll have to try that experiment. (laughs) Excellent. For one of your future classes. Yeah. Okay, so this one is, "Is it true," Fed Benavidas says, "is it true that using f/ "would diminish the picture quality?" That is a common question, and so we gotta walk very carefully on the equivalence police and other technical experts. I wanna make sure I say this exactly correctly. And so, closing down to f/ is gonna give you more diffraction, which is gonna lower the image quality. Yes, that is true. However, if I'm shooting a photograph, and I have a subject right here in the foreground, and I want it and the background in focus, and I go, oh, I can't shoot f/22, because it's gonna be lower image quality. Well, 16, that's kinda low. I'll go to f/11. Well, now my subject's out of focus, and I wanted it in focus, and so, it completely defeats what I was trying to do. And so, I use f/22, and I have no problems about it if I really need to use it. And so, don't use f/22 if you don't need it. And so, if I'm shooting a landscape that's kinda Grand Canyon, all far away from me, I'm not gonna use f/22. So, it's best to avoid 22 as much as you can; but, if you need it, you use it. Awesome, thank you. You have a question here in our studio, yeah. Okay, so I shoot with a Canon T5i, so you know what kind of camera. I've seen a lot, or heard a lot, about the Sigma 150 to Mm-hmm. Versus the Canon 200 to 400, and I shoot wildlife. What is your take on those two lenses? Okay. Kenna, watch out! The can of worms has just been opened, comparing one lens against the other lens! (Kenna laughs) Okay. So, I'm thinking you got one of your numbers wrong, because the Canon 150 to 600 is a very nice lens. They actually make two lenses. They make a contemporary lens, which is around a thousand bucks, which is a nice, kind of basic lens, and then they make a sport lens, which is about twice the price, made of much better construction, better sharpness, and it's one of these things where you pay double the price to get a ten percent improvement in quality. And so, that's the Sigma option. You mentioned the Canon 200 to 400, and I think you meant the 100 to 400, because this is the 100 to 400, and this would be more comparable in size. Take the lens hood off, just to get a better view of the size. The 200 to 400 is twice the size and four times the price, and it's a huge thing. And so, that Sigma versus Canon? I would say that, if you were looking at the Sigma sport version, which is the higher quality version of those two, it's a pretty hard comparison, because they both have different things to offer. The cheaper Sigma comes in at half this price, has more telephoto, and is a very, very good value. And so, when it comes to value, the cheaper of the two Sigmas is the better value. I like this one. Now, what type of work were you shooting? What are you shooting? Wildlife. Wildlife, okay. So one of the things to consider is, are you photographing a deer that is just kinda standing there, okay? Or are you photographing wild animals that are running around? If you're doing a lot of action photography where they're really moving quickly, the Canon is gonna have a better focusing system than the Sigma. If you were doing birds on sticks, on branches and stuff, then the Canon has that extra reach out to 600, and that's gonna be kinda nice for those small birds. If you're trying to do birds in flight, that's a lot of movement where focusing is more important. And that's where these lens decisions can get a little tricky, because you're comparing, well, one's got a little bit more reach, one might have a little better focusing, one's got a little different feel on it, and so it's not that one lens works and the other lens doesn't work. It's just slightly different variables on how they match up with your needs. Okay, thank you. I was just noticing there was such a huge different in cost. The Sigma was, around Christmastime, was, like, 980 dollars, Mm-hmm. versus the Canon was well over 1400 dollars, I think? Something like that, or even more. You're gonna have a fairly big difference, I think, in the focusing speed; so, if you are planning to shoot action, the Canon will outperform the Sigma by a fair margin. Thank you. Alright, John, well I know that the lens is just one big section within this class, but I know that there is so much more that you have taught on this. Can you tell us a little bit about some of your lenses classes that you have here on CreativeLive? Sure, let me go ahead and click that, 'cause I have a slide for that, as well. I gotta get past the slide that-- oh, here it is. So, I have such an affection for lenses that I had to create an entire two-day class; and, when I got into lenses, I said, you know what? They're just so different, we gotta have separate classes for both Canon and Nikon, and so, if you've wanted to learn about your lenses, and you have a Canon or Nikon system, I have a two-day class. We really get to geek out on this, and there's a lot of fun things that we did to go in and show every imaginable example from this, and so, if you wanna expand on this section of the class, this is kinda like an offshoot. It's not quite a sequel to this class, but it's an offshoot section that, if you really like lenses, and you wanna learn more about them and how to use them, there is much more information out there. And Canon and Nikon lenses. If you did not have Canon and Nikon, and you just wanted to learn more, it's not the worst thing to take these classes, because we're gonna be talking about focal lengths, and that's the same with any system, and, having said that, at some point in the future, I might make one of these classes for Sony lenses, and Fuji lenses, or the micro four thirds lenses, and so, depending on when you're watching this in the future, take a look, because there might be some more classes up by that time.