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Lesson Info

Canon Lens Focusing

all right, we need We're designing our lands. I got my design team here. We need to design a lands. Okay, let's start off really simple. The simplest type of design is where all of the glass elements move together. OK, so the entire unit moves forward and moves backward, and that's the easiest way to focus. All right, that's not the best thing in the world, cause there's a lot of elements moving throughout the glass and know what typically happens is that they're going to be mounted, mounted in a housing unit, and they move back and forth in there. And this is not really good. And this is actually the system that's being used in their 51 8 and you'll see some extension. As you focus back and forth, the elements go out and the elements come back in. And having that extension is not always the best thing, because that can cause a problem with filters and light are not like but water getting in, and he sort of dust in there. So moving all the elements. It's a simple system, but it's not t...

he most advanced system to use number of lenses use rear focusing elements, and so that is any sort of elements behind the aperture blades in the plants. And so where is our aperture blades? And some sort of group of lenses is moving back there. Moving now. That's going to be a whole lot easier for the autofocus system if you just have to move a few lenses back and forth, especially if they're back closer to the camera. In some cases, you might have inner focussing, where it just means that the front and element front and back elements are not moving at. Some group on the inside is moving back and forth, so I much prefer an inner focussing system to one. Where all the elements are moving back and forth typically means a more durable lens that has less extension and so forth on it. There's also cases where the design is just so complicated, and how they figure this out is mind boggling to me. Well, we need to move this element forward while we move this element back and things will stay in focus. How, I don't know. But this is what happens inside actual lenses. Look inside a lenses. You zoom back and forth or focus. Look at all the elements that are moving now. If you design a more advanced system, you might be able to reduce the size of your lands, which is going to make it a more attractive lens, my damn end up being able to do this in just such a way to reduce the aberrations and improve the quality of the glass and the image that we're getting. So lenses are designed for optimum image quality at one distance, and that distance is usually infinity. That's where our lenses air designed for being the sharpest, and when you focus up close, they're generally not as good. Macro lenses are the exception to that. In order to deal with this phenomenon, what they will do is they will sometimes include a floating element, and this is not directly a focusing element. But it will move with the focusing element in order to keep maximum sharpness where you are in the focusing scale, close up or far or further away, and so you'll see some lenses have a floating lens element. And is that a good thing or bad thing? Well, I guess thanks for putting it in my lens it would have been worse if it wasn't there. It's not a reason why you buy a lens or don't violence, but that's what's going on. I'm gonna improve the image quality I Q. What we often use for image quality. How smart ish your lands quality corrects for more of our aberrations problems. Lots of different types of operation problems, actually, and reduces the amount of flair if we have a floating lens element in there. So that could be very handy on many types of things and can reduce the distortion that we get when we focus up close, which is a problem with a number of lenses. Distortion gets worse. Now there's a number of lenses that use this floating lens system, and you'll notice on this list lots of macro lenses that says, this is a big part of this is improving it as we're focusing and changing your focus tremendously, which is what you are doing with macron lenses, rotation and extension. This is something that's not talked about a lot, and it's something that I like to know about my lenses, because if that front filter rotates, that means when I have a polarizer and I focused the lens. It's going to rotate my polarizing filter, and I don't like that lends extension. Does the barrel extend outward? Because if it does that, it might be sucking water and dirt back into my lands, and I would prefer that not to be the case. I would prefer it to be an internal zooming or focusing mechanism so we don't like the front filters that rotate, and it makes our lenses a little bit more mechanically vulnerable when they're extending back and forth. But you'll see it more commonly on the chief for lenses because it's easier to make those, and on the better quality ones, it'll be more internal. And so there's a number of lenses that have all internal movements. And so let me grab a lens real quickly for you here. This is the 72 202.8. Let me pull off the lens hood here, and so on this lens here, when we zoom back and forth, there's no movements or change in the size. When I focus, nothing changes at all, and that's that's a really nice system. That lens stays exactly the same size all the time. By contrast, a 100 to 400 different design lands different design needs on this one. When I zoom, there's obviously a huge amount of difference going on here. It changes the weight balance, and it moves the lens back and forth. You got a little something here. It's gonna drag it back in the lens. And so does that mean I'm not gonna buy this lands? No, but it's something I want to be aware of. And so there's a lot of lenses that very from the very inexpensive to the very expensive that have moving lens parts. And it's one of the things that I want to be aware of because I know I can't fully protect this in the rain, and I might want to be a little bit more precautious about shooting out in the rain with these lenses, then with these lenses over here. So lenses that have all internal movements are kind of like they get an extra bonus point when I'm looking at him. All right, that's something good that they have. And there's a number of zooms that have it. They're all L lenses. Number of the primes have it some of their special purpose lenses have it as well. Some lenses will have a focusing limit switch. This allows you to limit the area that your camera is hunting and looking for focus. And this becomes very helpful in sports photography and in macro photography. So, on this particular example, we have full What does that mean? Well, in this case for this lens, it means you can focus from two meters to infinity, which is where most people would leave the lands. Most of the time. This lens has a two meters to six meters. So if you knew you were on Lee shooting stuff close up and frankly, very few people ever use it here. It's really designed for six meters and beyond. If you're gonna go out and photograph a big field sports event most of the time, the players are gonna be more than six meters from you and year camera. If it's now in the six meter to infinity mode, isn't gonna bother searching in this mode. You know, when a little kid gets lost from their parents, the police come in to help out. Okay? Where do you think they are? I think he's in the park over here. We'll do you think he's over there? No. Okay. Well, then we're not going to search over there, cause that would take up a lot of time. We only wanna look where are subject is going to be. And so, in this case, we're identifying where are subject is, and we're narrowing our search parameter into that area. And so if you want to shoot sports and you know your subjects or six meters and beyond, this is gonna decrease the search area, which means it's gonna make your focusing a little bit faster because it doesn't have to search quite a Sfar macro lens us the same thing. Work out as well. You can do the full range from close up to infinity if you know you're only working with close up stuff. This is where the close up side of it really pays off. So your camera doesn't go search to infinity when you're trying to focus on a flower just a few inches in front of you. But you can also do half meter to infinity if you know you're not doing close up work. And so that's why a number of the telephoto and macro lenses have limit switch switches on them. On the topic of focusing, we've been talking a little bit about the focusing scale from time to time. This is a handy feature toe have, and one that I prefer to have on all of my lenses. I like lenses with focusing scales so that I can see where the lens is focused at. So if I want to manually set it at 10 meters, I could do it on my own. I like to be able to have that independence to do it. Now, as you focus with all lenses, when you focus, close up the lens moves away from the camera, and as you focus to infinity lens elements move back. And that is very apparent in this special lens that we're gonna talk about later. It's a macro. It's their M P E 65 this is a close up lands, and it's set to infinity right now and watch what happens as we focus up closer and closer and closer and closer and closer and closer, closer, closer, closer, closer, closer, closer, closer, closer. And so this is how far it's extending the lens elements so it can focus up very close, and it's becoming. It looks almost like a telephoto zoom lens, but this is not a zoom lens. This is a prime fixed 65 millimeter lens. It's always a 65 millimeter lens, but it's focused up really, really close right now. And so let's focus back to infinity. And the infinity is kind of the normal place that our lenses are designed for. And so that's kind of the normal retracted position that you would keep that lenses Nice to have all those teal pick and pull from whenever we need. All right, so one of the things about the distance scale is that you will be able to focus beyond infinity and beyond. Infinity is available because there's a little bit of heat and cold contraction that can change the focusing of your lens. And so focusing may or may not be at this affinity mark, you have to take a look through the viewfinder and see it yourself. Let me see if I could do a close up example with one of these lenses that give you a good example, and so I don't know if we can get close up, I'll stand up a little bit closer. And so this is the 35 millimeter 14 and you can see the focusing scale and I'll focus right at infinity. But it allows us to go beyond infinity. A little bet. And this is in case maybe we're focusing upon ah base camp on Mount Everest and the cold has really affected our lands and everything shrunk by a 1,000,000 of a millimetre, and all the lenses have moved ever so slightly, so that just gives us a little overlap so that we can still shoot infinity on our lenses. And so where this will play havoc with you is if you are shooting nighttime photographs and it's so dark you can't see. But, you know, you want to take a picture of the stars and you take your lands and you just racket to infinity. It actually gone past infinity, and so it's somewhere back, and that's where you kind of have to check things out in daylight. And so you have to be a little bit careful about when you're shooting your nighttime photographs. How are you focusing? There's a whole class and now, we're not gonna get into that now. Some of these lenses will have these little red marks for using infrared film or using infrared camera bodies or anyone who is doing infrared photography. Infrared light focuses at a different distance. Then the wave light that we see with their own eyes. And so you'll see this on a few select canon lenses. But very few some lenses have a close up range. Macro means close up macro means large, which means you're gonna photograph something large, and so it'll be listed on here. Now, what exactly does that mean? Is really important to me Because macro is a very general term. That means close up, and it means different things to different manufacturers. And so it doesn't give you exact distances in here. But it lets you know that you're getting closer. We're gonna talk more about macro in our specialty section, and we'll be talking about reproduction ratio and how to figure that out on your own lenses. Something else to be aware of as faras in the realm of focusing your lenses, is the focusing screen in your camera. They have made a change. When we went toe autofocus. They change the focusing screens on our camera because they wanted to accommodate for these slower lenses that were cheaper to produce. And they had to make a very tough decision. And the decision between Do we want a bright viewfinder or do we want an accurate view finder were not able to do both at the same time. And so what they decided to Dio is to go with a bright viewfinder so that it's very easy to see what's going on. And the end result is that if you use a very fast aperture, lands F to your camera is not going to show you the true shallow depth of field that you are getting from your final photograph. When you look through a fast aperture lands the depth of field that you see it in the viewfinder looks closer to F 2.8 than anything else. And so this is one of the reasons why it makes it very challenging to manually focus lenses faster than F 2.8. You have to be very, very good manual focusing in order to do it, and this is why auto focus helps out quite a bit and so just before warned that the depth of field you get is going to be shallower than what you see in the viewfinder. It's one of the rare times in the SLR you are getting something different than you actually see with your own eyes.