2.3 What Does A Bad Lens Look Like?
If you look around at all camera lenses, you will see that there's a vast price difference between different lenses. Generally more expensive lenses are better, but why? The easiest way to explain this is to look at what a bad lens look like. In this lesson you will learn about blurring, loss of contrast, chromatic aberration, vignetting, and distortion.
1.Introduction1 lesson, 02:27
2.How Do Lenses Work?3 lessons, 43:08
3.Special Lens Features1 lesson, 09:35
4.Choosing a Zoom Lens5 lessons, 44:07
5.A Guide to Prime Lenses2 lessons, 26:57
6.Getting Perspective Right in Your Photographs3 lessons, 35:17
7.Conclusion1 lesson, 02:22
2.3 What Does A Bad Lens Look Like?
If you look around at all, at photo lenses, you will see a vast difference in the prices. Generally, more expensive lenses are better, but why? The easiest way to explain this is to look at what a bad lens looks like. Because a good lens is a lens that does not exhibit the characteristics of a bad lens. Lenses are only good compared to other lenses. In this lesson, you will learn about blurring, loss of contrast, chromatic aberration, vignetting and distortion by taking a look at some crappy lenses. First up, let's look at blurring. In photography, we want to capture as much detail as we can. If we want to selectively blur our image in post-production, we can. But, it makes sense to start with something sharp. Blurring in lenses is not the part of the image that is out of focus. It's either motion blur, or a lack of sharpness from the lens. Let's take a look. For this example, we're gonna be taking a look at two photos that I took at about 18 millimeters. I'll show you the properties here. Right there, 18 millimeters. And they're obviously of a brick wall. And I chose to do a brick wall because it's flat. And it has a lot of detail in it. If you're looking at this photo like this, you're kind of seeing the entire thing. And it doesn't really look too bad. You're not seeing blurring. But if you are a pixel peeper, which means you like to look at things at a one to one pixel ratio, then you're gonna see something different. So if I zoom up here, and now we're looking at 100%, in the center this looks fairly decent. But as I scroll over here, especially to this corner, usually images are the most soft in the corners so that's what we're gonna check out. You're gonna see that there's a noticeable drop-off in sharpness. Right here we're still pretty sharp, but right around here you're saying it's like someone smeared some jelly on the lens. Now, we're gonna compare this with this image right here. And we're gonna go up and check out what's happening in the corner here. Now, both of these images exhibit blurring, but one of them looks much worse. And the one that looks much worse is the cheap kit lens that came with my very first DSLR. It's a Canon EFS 18 to 55 millimeter F3.5 to 5.6. And it's not a very sharp lens. Now, this particular photo was taken at F 3.5, and of we check out the other photo here, the other photo was taken F 2.8. So, this photo here was taken at F 2.8 and you're seeing some blurring, but check out the difference between this photo and this photo. Can you see the difference there? This guy right here goes from. You know, this is looking okay. You can actually see, though, right on the edge of this photo, especially in the corners that it goes from okay sharpness if we zoom right up in the center. This is reasonable sharpness, but as you go towards the edge, whoa, this gets way out of control in the blurring department. I mean, that's just bad. But even if we take this image, and then we'll go back here, and we're gonna just zoom up right on the center of this one. Then we'll go back to this one, we'll zoom right on the center of this one. Check out the difference between this, and this. Now they're not. They're not exactly the same because I think I bumped the tripod a little bit, but just look at the difference in sharpness, and this is comparing center sharpness. And on a lens, lenses are usually the sharpest dead center, okay? So this lens right here is clearly better. And it's also better, as we just saw, in the corners. But overall, this second lens has an issue with blurring. It's just not as sharp as a better lens, a more high quality piece of glass, even in the center. Now, this is an awful sharpness, but it's certainly not as good as this. You can see this is much sharper. You can especially tell if you look at the details in the shadows right here. Just look at how sharp these shadows are rendered right in the center. 'Kay? So, keep your eye on that. And now we go to the second one, you can see there's more, just very slightly more of a gradation there between these two images. I mean, they were taken probably less than 15 seconds apart. So there's no shift in the lighting. In fact, on this day these was zero clouds in the sky. So, it's the exact same lighting. There's no softening of the light. And you can see that this second lens here we'd call kind of a crappy lens. It's awful on the edges and in the corners. And even the center sharpness is not as good as a more high quality lens. Now the second lens here is a sigma 17 to 50 millimeter F2.8 so it's a constant aperture lens, and it's showing you sharpness at a more wide open aperture. If we were to look at this photo here. Let me just pull this up so you can see. This shot is with that same signal lens, but now it's a F3.5. And usually, as you stop a lens down, it's going to become sharper. So now they're at the same exact aperture. They're both at F3.5. And this second shot here, is probably gonna look maybe just a hair sharper. It may not be perceivable that much, but if we look in a corner here, you can see in the extreme corners, it is showing you some sharpness. And usually, unless you're talking about the very best lenses, you're usually gonna see a little bit of blurring in the corners, especially with zoom lens, prime lens maybe not so much. But you can see, even in the center of these two images, if you were to only have this as your reference point you'd say that's okay, but compared to this you'd say eh, that's not so great, right? It's not like ridiculously sharper, but if we were just to go over, you know, just, we are still in the middle here and we are gonna look at the edge performance. So not the corner, we are just looking at the edge now, and so this is the kind of, the cheaper, crappier lens, and this is the better lens. You can see, it looks much sharper. So, that right there's what blurring looks like, and better lenses will do a better job with sharpness and it won't exhibit as much blurring, especially in the corners, and on the edges of the images. One of the things that makes a lens great is nice looking contrast. Contrast is detail and lenses that have poor contrast performance, just like blurring, lack detail. Let's check out an example. In this example we're gonna look at the difference between two different lenses again, on this picture of this desk here that I took, and I kind of back lit this with a studio strobe. And you can see here, we have picture A and picture B, and they look really quite similar. The image shifts just a hair, but you know, they're, they're pretty close. They're both taken at about 50 millimeters at somewhere, I think, around F 5.6, right? Yeah. Again, just like the last image, if you're looking at the full image here, they both look okay. You can't really see a huge difference. What we're looking at is contrast, right? The difference between light and dark. Both of these were taken with the same flash setting, so it's going to be very very consistent between these, cuz this is not a battery powered speed light, this is a studio strobe, so the consistency between these two shots is gonna be pretty good. But just look at the difference between the contrast. Now, this second one is obviously sharper, right? That's pretty plain to see. But what we're looking at is the difference between the contrast of these two images, which is pretty subtle, right? I mean, this one isn't awful, but this one you'd say, that's better. And what I'm seeing is that this one looks punchier. The colors look a little bit more deep, it just looks a little bit more contrasty. This one just looks flatter and particularly, I'm looking at this area right here. I'm looking at the color tones in here and I'm looking at the general kind of difference between the light and the dark tones in here. Especially compared to this outer, non-shadowed area here where it's getting the direct light so, if we look at this and then we go to here, this to me just looks like it has better contrast. You can just see that the tones in the second image just look punchier, they look deeper, they look richer, right. And that's another difference that you will see between crappy lenses and better lenses. Chromatic aberration is a type of distortion in which there is a failure of a lens to focus all colors to the same convergence point. Put simply, chromatic aberration is a smearing of the colors you can see on the edges of objects. Let's take a look. Already in this example we're going to look at another pair of images here. And this time we're looking at chromatic aberration. Again, if we're looking at the whole image, chromatic aberration is not going to be a huge deal. Right? It's not gonna be something that if you post your pictures to Facebook or if someone's looking at a smaller image, a smaller print, chromatic aberration may not be a huge deal and it can be corrected, to some degree, in Photoshop, Lightroom, Aperture, something that processes raw images, or even JPEGs for that matter. It can be corrected, but much better to start with an image that has less of it, because as you're gonna see in a second, chromatic aberration does affect the image pretty drastically. So, what we're gonna do here is we're gonna punch in to this image. You can see that this image looks pretty good. Now, particularly where we're gonna see chromatic aberration is between high contrast points. So, on this lens we are seeing chromatic aberration right here, it's red between this white part and the dark part here. You can see there's a little red haze here. And around other parts of this image you're gonna see that crop up as well. It's not too bad, but you, you are gonna see it. For looking in the trees here, between leaves in the sky, which is very high contrast, we can see a little bit of chromatic aberration. It's very, very subtle, very subtle, but we can definitely see along this super high contrast edge right here there is chromatic aberration. Now, let's compare that with this image and if we punch up here, we're gonna see something completely different. Now, first let's look at this leafy area here. What you're seeing here is a different kind of chromatic aberration. And this is more commonly referred to as purple fringing. And, just like the other image here, this is chromatic aberration of the more red wavelengths of light. And this is chromatic aberration in the more bluish ends of the spectrum. This lens is not focusing the violet wave lengths properly, which is why, why we're getting this purple fringing. Now, you can see that we are getting purple fringing here along the same points that we were on the other lens. But this lens is terrible. I mean, this is awful. Every single high-contrast point looks like we smeared Vaseline on it. I mean, that's not good. For one, this lens is not nearly as sharp as the other lens but even if it wasn't as sharp, we're still seeing chromatic aberration just ruin parts of this image, especially these real high contrast points in the trees here. It just looks like there's a big, giant, purple glow around everything. Now, we can clean this up a little bit in a photo processing application, but this is pretty bad. Now this lens I also got with my very first DSLR. This is a Quantaray 70 to 300 millimeter zoom lens. I believe it's F4.5 to 6.3 or something. This is a Canon 70 to 200 millimeter F 2.8 IS. I think that Quantaray lens cost about a $160. This Canon lens costs over $2,000. This is a Canon L series lens. That's one of their professional quote unquote lens. But there's a huge difference in a crappy lens versus a professional lens like this. Right? You can just see that's a huge mess. And that's really not so bad. Big difference there. Higher end lenses use LD or low dispersion glass that contain fluorite. These hybridized glasses have very low levels of optical dispersion thus resulting in less chromatic aberration. Next, let's look at vignetting. In photography and optics, vignetting is a reduction of the image's brightness, or saturation, at the periphery, compared to the image center. Many lenses have vignetting, when set to their maximum aperture, but lower quality optics will have more. Vignetting also usually gets better as you stop the lens down. Let's take a look. In this example, we're gonna be checking out vignetting. Now, I've taken two photos of something very interesting here. It's just a plain white wall and, and the white balance was not set properly on my camera so it actually looks yellow. But that doesn't really matter because what we're gonna be looking at is how vignetting on these lenses is affecting our image. And the reason that I shot a, let's say it's a yellow wall here, is that when you're shooting in the real world vignetting is often much more difficult to see. Because you don't know if you're seeing vignetting or the natural fall off of light in that particular area. So, we shoot something that's a solid color that's lit extremely flatly so that we can see what the lens is actually doing. Now, this image does not look like it's displaying any vignetting. But if we look at this other image. Now we're seeing something different. We are seeing a definite darkening in the corners and along the edge of this image. Now, we're gonna see vignetting more on the sides than we will the top, because this imager is wider than it is tall, which means as we get closer to the edges of the projected image circle, we are gonna see more vignetting and we're going to get closer on the sides than we are at the top because this is wider. I should say that crop sensor cameras do much better with vignetting than a full frame or larger sensor camera. Especially if you're using non crop lenses or non digital lenses because these are projecting an image circle appropriate to fill a full frame camera. And these photos are in fact taken on an APS-C sized camera which means that the full image circle is larger than this imager. So we're not seeing as much vignetting as we would on a full frame camera, if we stuck these same two lenses on a full frame camera, we would see more vignetting probably out of both lenses. Especially out of this one because this is obviously pretty bad. But, if you can imagine as it gets darker here, on a full frame we just extend this out farther, and we'd see more darkening of the image. So it's going to be more prevalent when you're using a larger sensor and a lens that's designed for a larger sensor. Now, if you're using a crop sensor and a digital lens that means that the image circle is going to be made to just fit that imager on a crop sensor camera which means you're going to see more vignetting as opposed to if you used a regular lens. But still, on a Crop Sensor camera, vignetting is something that you will see in lenses. And you can see between these two images, although it's subtle, this one definitely has a darkening on the edges of the image. Distortion is another effect that can be present on many lenses. There are two major types of distortion, barrel and pincushion. In barrel distortion, image magnification decreases with distance from the optical axis or center. The apparent effect is that of an image which has been mapped around a sphere or barrel. In a zoom lens, barrel distortion appears in the middle of the lens' focal length range, and is the worst at the wide end of the range. Let's take a look. So, let's check out what barrel distortion looks like. We're looking at an image of the brick wall again that we looked at earlier, but this time we're gonna be focusing on what's happening to the distortion of this image. Now, sometimes barrel distortion is hard to see until you compare it with a corrected version. Okay, so this is that same image and this a photo taken with the Canon EFS 1855 millimeter lens, and this is the corrected distortion version. Okay, so I took this into Adobe Raw Camera Processor in Photoshop. And I corrected for the lens's distortion, based on the automatic settings that it provides from the profile of this lens. And so you can see, as we toggle between these two images, this is what barrel distortion looks like. We get this kind of bulge of the image towards the center where it looks like the image is being mapped around a barrel. And that's where the term barrel distortion comes from. Okay? Now here's two more examples, all right? This is another lens, this is the Sigma 17 to 50 millimeter lens and this is the original, non-corrected version, and this is the corrected version, okay? And you can see, as we go from this image to this image right here, this is the Canon, this is the Sigma, all right, Canon, Sigma, that the barrel distortion is much more pronounced on the cheaper Canon lens. Now, that may be partially due to the fact that the Canon lens is a little bit more of a variable focal length lens. So that's 18 to 55 millimeters where this is 17 to 50 millimeters, okay? So it's a little bit more telephoto and as lenses have more of a telephoto range, the more zoom range you have in a lens, the more distortion you can expect at the long and short end of the focal length. So, that is probably why this lens, here we are looking at the non corrected version again, looks a little bit better than this right here, we are seeing much more distortion and the less correction that has to be made, the better the result will be, because you will get less stretching of the image and that's gonna look a good bit better. In pincushion distortion, image magnification increases with distance from the optical axis, or center. The visible effect is that lines that do not go through the center of the image are bowed inward, toward the center of the image, like a pincushion. Let's take a look. In this next series of images, we're gonna be looking at pin cushion distortion. Pin cushion distortion usually occurs at the longer end of the focal range, okay? So, in this particular image we're looking at the side of a building, and this is shot at 200 millimeters. And this was shot with a Tamron 18 to 270 millimeter lens. So that's a super zoom lens, which we're gonna talk more about later in this course. And what we're looking at here is the pin cushion distortion. This image here is the no lens correction version. Now, all four of these images have been corrected for their perspective, just so I can get them lined up pretty similarly. But this image has not had the lens distortion corrected in it. And so, just on the surface here, it's kind of hard to see what's going on, but if we compare this to the corrected version, you can see that there is definitely some pin cushioning going on. Now, the center of the image looks like it's being squinched, or squished. And that is the pin cushion distortion. So we get this kind of shrinking towards the center of the optical axis, or, basically, the center of the image. Now, let's compare that to this image right here, which looks a little bit different. This is shot with the Canon 70 to 200 L lens, the IS lens. And this is the non-lens corrected version. And this is the corrected version. You can see the difference between these two is very slight compared to this guy right here where it looks like there's a little bit more of the pin cushioning happening. Now, there is pin cushioning in both of these, but over here, with the Tamron lens, there's a little bit more. A lot of times, when you're looking at reviews of lenses, they will talk about how well a lens handles vignetting, chromatic aberration or distortion. Now that you have a better understanding of what these things look like, you'll be better informed when choosing a lens. In the next lesson you will learn about some special features in lenses like stabilization, lens codings, and fast focusing motors.