Lessons

Lesson Info

Lens Sharpness

All right, continuing our quest through focusing, we also need to talk about lens sharpness. Let's just use Nikon for an example here. They make an 18 to 55, and they make a 17 to 55 lens. Somebody who didn't know about photography would say isn't this a little redundant, Nikon? Why do you need a one millimeter difference in lenses? It's a lot more than just the one millimeter difference that's the difference between these two lenses. They have different focusing systems in it, mechanically they're built very differently. One's designed to be a lightweight, easily, low-cost lens for an entry-level photographer to use on a camera. Another is more of a professional, high quality, top-of-the-line product. When they make a lens, it's just a series of compromises. We can do this, but we give up this. We get this, we gotta give up that. So, they have different lenses to go for different types of needs. Now, each of the manufacturers do have their premium brand, or premium line of lenses, and...

it goes by either different names, or stripes or letters that they put on their lens, and some cases it's a very gray scale where one might not quite not make it to that cutoff, but it is practically that good in quality. Maybe it doesn't meet it for some other reason. Canon, for instance, will put a red ring around their lenses and in order to get the red ring, it has to meet certain specifications. One of the things that it needs, and I'm forgetting the exact number right now, I think it needs two exotic glass elements in it to adhere to that need. Why? What if the lens is really, really good and doesn't have any exotic elements in there? Well, it can't be an L-Lens then, you know. Nowadays, the L-Lenses with Canon have a certain amount of weather sealing, but they didn't at one point. So, the top of the line lenses don't need anything in particular for sure, but it is one of their highest and the best that they can do type lenses. Look for those if you are looking for the highest sharpness in lenses, but it's more than just sharpness. It's the quality of construction and the variety of features that you're going to get from those lenses as well. I like 'em just because they are tools that work well and they're comfortable to use. It's not just the fact that they actually do a good job, but it's the type of tool that I like having in my hand and working with. They're well built and it's nice that they're also quite sharp. Another thing that we talked about before was what is the best aperture to shoot at if you're not needing more or less depth of field? This of course is where we run into the problems where lenses are slightly imperfect when they are shot wide open and we get diffraction when we close them down. And lenses tend to be sharpest towards the middle of the apertures, so you may wanna do a test on your own lenses. Shoot the brick wall test, which is a really boring thing to shoot, but it will show you if it's sharp or not. Shoot it at all the different apertures and see what aperture you're getting the greatest sharpness on, so that when you do photograph something that is flat or relatively flat, you know which aperture to go with. It's usuallly the middle of the range. Sometimes it's two or three in from wide open. It depends on the lens. Lens sharpness can also be charted in an MTF Chart, and this is often, sometimes put out by manufacturers that show how their lenses perform. Now, I guess the first thing to know about these is that most of these are theoretical and not actual tests. It's kinda beyond me. It's not my area of specialty, that you can design a lens, we're gonna put this element here, we're gonna put this element here, we're gonna coat it with this, we're gonna put this inside the housing, we're gonna send light through it, and this is how sharp it's gonna be. They can figure that all out by math ahead of time. All right? This is what they put into a chart. This is what a good lens looks like and here's what a less good lens would look like. Here's how you read an MTF Chart. They're actually very, very easy to read. Zero is the middle of the lens. The bottom chart is telling you how far away from the middle of the lens would you go out on the lens. So, out here at the edge, it reaches around and then somewhere around 24, 'cause that's how far you can get when you go from the middle of a full-frame lens out into the corner. Point-- 0.6, everything above that is considered to be sharp. Everything above 0.8 is considered to be very sharp, so what we can see is on the left, everything is very sharp from the middle of the lens out to the edges. And over on our chart on the right, it's sharp in the middle, but then it's not so sharp when you get off to the edges here. Now, each line, depending on who produces the chart, will have a different meaning. All right? So, what it might mean is one line is for f/2.8 and another one for f/ 'cause there's different sharpnesses 'cause things change in lenses. One might be looking at different types of contrast or lines in different directions, and you're gonna get different results with each of these. That's why you end up with all these lines and typically what you want is you wanna bunch of straight lines that go across the top of the frame. But there is no lens that does that. There are some that don't waver too much, but the ones that are uneven, the ones that are separated, the ones that curve way off, those are the ones that are typically lower in quality. Here's a bunch of different actual MTF Charts for a variety of lenses out there. Now, how much does this affect me when I purchase a lens? It has almost zero impact on whether I choose to buy a lens or not. It's kind of interesting to compare one lens against another, but I have never not chosen a lens because of this. I have not chosen to shoot and I have sold some lenses that I wasn't happy with their performance. That may or may not show up in something like this. But it is more just kinda for the nerd in all of us who wants to compare statistically how sharp a particular lens is. Let's see, what else, what lenses do we have here? The Zeiss Otus 55 1.4 down here in the right-hand corner, that is something that they purported to be the highest quality 50 millimeter-ish lens that has ever been produced. So, if you said, well, this isn't good enough for me, well then you can give up photography and go do something else, because there is no lens that will do sharper than this at 50 millimeter lens and what they do. The Nikon 58 1.4 came out and it was supposed to be one of the best lenses ever, and when it comes to just absolute sharpness, it's okay. There are some other things it does really well and some good reasons to buy it, but sharpness wise, eh, it's just, it's good, it's good. So, it's something that you can take a look at and something that you'll see a lot of times when lenses are introduced. Another place that you can go to check out lens sharpness is DxOMark, which does a bunch of testing on different lenses, so I wanted to pull off a few of the top lenses and bottom lenses to kinda show you what things are. Now, there are some different ways to filter this. You can filter it by which camera you shoot it on and some other parameters, so my results might vary slightly from yours, but it's the general idea that I wanna get over to you. All right, so when we look at Canon's top five lenses, the things that I notice first off, where are the zoom lenses? As I said before, prime lenses tend to be sharper. Let's look at the bottom. Ah, there's the zoom lenses. Okay? (giggling) Typically, more, lenses that are trying to do too many things or lenses that are just low price and that's the market that they're in. Let's take a look at some of Nikon's top lenses. We're gonna notice a lot of prime lenses here. In general, it's easier to produce a telephoto lens than it is a wide-angle lens and get it corrected. If you look at the top lenses here, we have all telephotos over here and we have three out of five telephotos with Canon there. So, a lot of telephotos, they're just easier to manufacture, they tend to score better. Once again, a lot of zoom lenses there on the bottom of the list. Let's not be too centered on Nikon and Canon. I know Sony lovers out there. Once again, we're seeing a lot of prime lenses, a lot of telephoto lenses, and then we have kind of lower-end, basic lenses out there. One of the worst lenses on Sony is the 16 to 50 lens, and I own a copy of it. Because it's a really small lens and for, if you want a really small camera package, it's a nice lens. What they've done and something that we're seeing more and more in manufacturers, is they can produce quote, unquote, a bad lens and they can fix it in post-processing at the time you're shooting it. That lens, it's kind of interesting, you mount it on the camera and you turn the camera on, for a quarter of a second you get to see what it actually sees and it's this distorted view of things, and then it all of the sudden jumps back and has everything perfectly corrected. They're running software that fixes the distortion as you shoot, as you look through the camera. There is kinda this whole thing about do you want the lens to be perfect or do you want the image to be perfect? Because if they can manufacture a lens and they like, well we can make this lens a hundred dollars cheaper if we fix it in software. Or maybe we can make the lens lighter weight and we'll fix it in software. So, in theory we could put on some really poor lenses and fix it in software. Now, there are some things that are hard to fix in software and we like our lenses to be as good as possible, and if we take that lens and for some reason we want to adapt it to another system, non-Sony system, it's not gonna know how to fix it. So, we like our lenses to be as good as they can, as best they can. For the Micro 4/3rd's users, what have we seen? Lots more prime lenses, a lot of their pro and their elite lenses, and then we have some more of their zoom and lower-end lenses down here. Now, kinda just run the chart over everything, what is, what are their really sharp lenses? We're looking at all telephotos, all prime lenses, some of them are pretty fast. Then bottom lenses or some kind of low-end zoom lenses. There's a strange body cap lens, which is like a joke of a lens from Olympus, but it's kinda fun 'cause it can do its own thing. It's not designed to be sharp. So, if you wanna check out how sharp your lens is, you can go check them out on their website. I'm not associated with them, I just, it's an interesting place to check data. It doesn't really affect which lens I choose out of my camera bag for which picture I wanna take, but it's kinda nice to be able to compare some of these things when you are looking at different products out there.