Canon® Lens Focusing
All right, we need we're designing our lands. I got my design team here. We need to design the lands. Okay, let's, start off really simple. The simplest type of design is where all of the glass elements move together. Okay, 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 now what typically happens is that they're going to be 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 fifty one eight 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 or 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 no...
t the 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's 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 auto focus system if you just have to move a few blends is back and forth especially if they're back closer to the camera in some cases you might have inner focusing where it just means that the front and element front and back elements are not moving it some group on the inside is moving back and forth so I much prefer an inner focusing 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 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 is 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 lands I might 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 are 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 lindsay don't violence but that's what's going on I'm going to improve the image quality like you what we often use for image quality how smart is your lands quality corrects for more of our aberrations problems lots of different types aberration problems actually and reduces the amount of flare 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. The distortion gets worse now, there's a number of lenses that used 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're doing with macro lenses. 00:04:02.51 --> 00:04:05. Rotation and extension us is something that's not 00:04:05.01 --> 00:04:08. talked about a lot and it's something that I like 00:04:08.27 --> 00:04:12. to know about my lenses because if that front filter 00:04:12.39 --> 00:04:15. rotates that means when I have a polarizer and I focus 00:04:15.17 --> 00:04:17. the lens it's going to rotate my polarizing filter 00:04:17.45 --> 00:04:20. and I don't like that len's extension does the barrel 00:04:20.75 --> 00:04:23. extend outward because if it does that it might be 00:04:23.37 --> 00:04:26. sucking water and dirt back into my lands and I would 00:04:26.5 --> 00:04:29. prefer that not to be the case I would prefer it to 00:04:29.1 --> 00:04:31. be an internal zooming or focusing mechanism so we don't like the front filters that rotate and it makes our lens 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 seventy two two hundred two point eight 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 one hundred four hundred 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 going to drag it back in the lens. And so does that mean I'm not going to buy this. Land's? No, but it's, something I want to be aware of. And so there's a lot of lenses that vary 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 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, alright, that's. Something good that they have and there's a number of zoom's that have it. They're all l lenses number 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 land's most of the time this land's 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 going to go out and photograph a big field sports event most of the time the players are going to be more than six meters from you a 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 help out okay where do you think they are? I think he's in the park over here well 00:07:34.748 --> 00:07:37. you think he's over there no okay well then we're 00:07:37.53 --> 00:07:38. not going to search over there because that would 00:07:38.82 --> 00:07:41. take up a lot of time we only want to look where our 00:07:41.55 --> 00:07:45. subject is going to be and so in this case we're identifying 00:07:45.09 --> 00:07:47. where our subject is and we're narrowing our search 00:07:47.68 --> 00:07:50. parameter into that area and so if you want to shoot 00:07:50.33 --> 00:07:52. sports and you know your subjects or six meters and 00:07:52.88 --> 00:07:54. beyond this is goingto 00:07:55.6 --> 00:07:57. decrease the search area which means it's going toe 00:07:57.95 --> 00:07:59. make your focusing a little bit faster because it 00:07:59.89 --> 00:08:02. 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 limits which switches on the 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 to 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 ten meters I could do it on my own I'd like to be able to have that independence to do it now issue 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 going to talk about later. It's, a macro it's, their mp sixty five and 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, closer and closer and closer. Okay 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 sixty five millimeter lands it's, always a sixty five 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 lands. Nice to have all those pick and pull from whatever 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 lands 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 thirty five millimeter one for and you can see the focusing scale and I'll focus right at infinity but it allows us to go beyond infinity a little bit and this is in case maybe we're focusing upon base camp on mount everest and the cold has really affected our lands and everything shrunk by a million 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. 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 in that 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's doing infrared photography. Infrared light focuses at a different distance, then the wave light that we see with our own eyes. And so you'll see this on a few select cannon 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 going to 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 auto focus they change the focusing screens on our camera because they wanted to accommodate for the 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 one two one for one eight f too 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 aft two point eight than anything else. And so this is one of the reasons why it makes it very challenging to manually focus lenses faster than f two. Point eight. 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.