Skip to main content

Canon Lenses: The Complete Guide

Lesson 24 of 58

Lens Autofocus


Canon Lenses: The Complete Guide

Lesson 24 of 58

Lens Autofocus


Lesson Info

Lens Autofocus

we've been dealing with focus. Let's do the world of auto focus. So in this case, we're gonna have these little contacts which connect up with the electron ICS on our camera. And there's different numbers according to what lens and what needs they have. It typically has to do with whether they use their used with tele converters or not. You'll Seymour of these contacts when they're used with tele converters. And so this is what is transmitting data information as well as power from the cameras to the lands. And so motors for focusing are built into the lands and their optimized according to the needs of that lens, which is why they went with this whole e f system. Proximity equals efficiency. The closer the motor is toe where it actually needs to do the work means the more efficient it will need to be better battery life. It will be able to be used with different extenders, which is reasons why they went with the system. Their original focusing system is an art form drive system. We're...

not gonna get into the specifics of it because we don't need Teoh, but in a very general sense they were slow and noisy, and they sounded like a squeaky wheel. And so if you get one of the older lenses, it doesn't sound nice and smooth. All right, and there was no manual focus override when your camera was in auto focus. You couldn't grab the focusing ring and just start turning. You had to use the manual switch to get it over into the manual. The next little improvement they made is they made it into a micro motor, which reduced the size of it and reduce the price of it a little bit. And they were able to put it in some of their cheaper lenses. And so this is something that you might see on some of their very old lenses. And this is a very traditional electric motor, just driving a gear train. So it's fairly traditional technology. No manual focus override, either. So if you're in autofocus, you gotta flip the switch in order to manually focus the lens. And there still are two lenses out from the original cast of characters who introduced the F system there, 52.5 micro and their 1 35 to 8 soft focus. They're not real common. They should really, really be replaced or something. But they're still using these older motors. There's a few of the lower end lenses that air using these micro motor lenses, and they're all lenses that are gonna be kind of on the second tier of auto focusing quality. So these this list of lenses down here in the lower left corner not my first choice if I was gonna be shooting professional sports, maybe my last choice. And then everything got better with us. Ultrasonic motors are these very fast and quiet focusing motors, and they started with a ring type USM or ring us em. And then they modified it and called it a ring. Type us and we're not gonna get into the details of it, but it's what they're currently using, even in their up to date lenses. They didn't making a smaller version of it, and then they made a smaller, improved version of it. But it's the ring type USM that is in most of the lenses that are being made today. And the reason they went with this type of system it is very quiet, is very fast. It has a lot of torque so we can get up to speed very quickly. It's very efficient, so it's good on battery power. It's small in size, it can go fast, it can go slow and it works under a wide number of conditions, and it allows us to manually grab the focusing ring and move it whenever we want. And so this is kind of the standard for focusing, and this is what other companies have followed in, and this technology hasn't really changed that much, so there haven't really made improvements. They've made some ways of making it smaller and cheaper. But the basic good ring type USM hasn't changed much at all in the last 20 years, so there are a few lenses that are using their smaller, cheaper version of their focusing motor. This there's this junior version and it is really hard to find factual data on what motors are in the lens because this says ultrasonic. But it's actually using the micro ultrasonic motor, and I have dug in and I've got all the information and when you get the class, you get the notes that have all this information in there. In case you're wondering And so this this 300. You can't just grab this focusing ring and turn it whenever you want, because when it's an auto focus, the gears are engaged and you start burning the motors, and it's not a good thing. Now they did make a special exception. These are the only two lenses still using the micro us and motor. Is that on the 51 4? It does employ a special clutch in their that allows you to just pick that lens up and manually focus whenever you want. However, this lens is notorious for having focusing problems because it's using this old focusing motor with this special clutch system. So if you talk to somebody who's out of 51 4 you'll probably hear about Kennedy. You have personal experience with this. I did. I did have that lens and even versus you know, the 1.8 it had, you know, some tough focusing issues there. So it is a truth. Damon, alright, didn't just make this one up, all right, so the latest one that they've introduced is the STM, the stepping motor. They will sometimes advertises as smooth transition for motion if you remember when we were talking about still photographers versus cinematographers, and their needs for focusing are different because, as a still photographer, I don't care what happens between focusing on A and focusing on B. But for shooting movies, it's really important that it's smooth and these ultrasonic motors that are great for still photographers. They're not so smooth in the focusing, their just quick, and these are much smoother. And they are a little bit better for shooting movies in an amateur, since this is not what the professionals or shooting with. And so they're fairly quiet the ultra Sonics required as well. But mainly it seems like these were designed so that you could focus while you were shooting video, and it had a smoother focus back and forth. And so this would be more for Mom and Dad filming the kids down at the park. Just you know, you have your DSLR. You want to shoot video. You want to shoot autofocus while you're shooting your video for home movies. Then that's gonna work out quite well. The STM motors work fine for that. For still photography, the STM motors are a bit of a toss up as to how good they are. I would take a USM over an STM any day. The question is, is what? I want this over something else and it's It's okay. It's just not. It has one feature that I'm not particularly fond of, which is a fly by wire manual focusing system, which means when you turn the manual focusing, you're not actually directly engaged with the lenses you're turning electron ICS, which is telling the lens to moves, move so there's a slight delay as you do it. It's not quite directly linked to your finger movements. And so that's what this focus by wire is. And one of the downsides of this is that when you leave your camera turn, if you have your camera turned on, you focus and then you turn your camera off. You're like, Oh, I need to focus back to infinity. I want to retract the lens. It won't work because there's no power to the lands. And to manually focus, you have to have power to the lens when this is turned on. And so the STM lenses is relatively short, but they seem to be employing the STM, focusing system on all their new lower in lenses. And so I think this is their new de facto focusing system for their lower in lenses. So full time manual focusing, this is a great feature. It was one of the big hits in the early days of auto focus, with can in the lower Inland says, Do not have this. What this enables you to dio is that if you are in auto focus, you can just grab that focusing ring and turn it whenever you want. And it's not gonna damage the lens, and you can smoothly focus it as you wish. And so this is a great feature. It's something that's going to be on their medium toe, higher influenzas.

Class Description

Working with interchangeable lenses can be both exciting and daunting to all levels of photographers. Canon® Lenses: The Complete Guide with John Greengo will prepare you to select the right lens and get the most out of all of your lens investments.

John Greengo is the master of making complex photography concepts easy to understand and in this class, he’ll bring all of your Canon EOS DSLR lens options and operations into focus. 

You’ll learn about: 

  • Focal length and aperture
  • Canon zoom lenses
  • Which lens accessories to buy
  • Third-party lenses
  • Maintaining a lens system

John will cover the full range of Canon lenses, from ultra-wide to super-telephoto, zooms to primes, fisheye to perspective control. You’ll learn how to match the right lens to your needs and get insights on the best ways to use it.

Whether you are thinking about buying a new lens or just want to get the most out of what you already have, Canon Lenses: The Complete Guide with John Greengo will help you out.


  1. Class Introduction
  2. Canon Lens Basics

    John Greengo gets you up-to-speed on the basics of working with interchangeable Canon® lenses.

  3. Focal Length: Angle of View
  4. Focal Length: Normal Lenses
  5. Focal Length: Wide Angle Lenses
  6. Focal Length: Telephoto Lens
  7. Focal Length Rule of Thumb
  8. Field of View
  9. Aperture Basics
  10. Aperture: Maximum Aperture
  11. Aperture: Equivalent Focal Length
  12. Aperture: Depth of Field
  13. Aperture: Maximum Sharpness
  14. Aperture: Starburst Effect
  15. Aperture: Flare
  16. Aperture: Hyperfocal Distance
  17. Camera Mount System
  18. Canon Lens Compatibility
  19. Canon Lens Design
  20. Canon Lens Composition
  21. Canon Lens Shape
  22. Canon Lens Coating
  23. Canon Lens Focusing
  24. Lens Autofocus
  25. Canon Lens Image Stabilization
  26. Canon L Lenses
  27. Image Quality
  28. Canon Zoom Lenses: Standard
  29. Canon Super Zooms
  30. Canon Wide Zooms
  31. Canon Telephoto Zooms
  32. Prime Lens: Normal Lenses
  33. Prime Lens: Moderate Wide
  34. Prime Lens: Wide Angle
  35. Prime Lens: Ultra-Wide
  36. Prime Lens: Short Telephoto
  37. Prime Lens: Medium Telephoto
  38. Prime Lens: Super Telephoto
  39. 3rd Party Lenses Overview
  40. 3rd Party Prime Lenses
  41. 3rd Party Zoom Lenses
  42. Lens Accessories: Filters
  43. Lens Accessories: Lens Hoods
  44. Lens Accessories: Tripod Mount
  45. Lens Accessories: Extension Tubes
  46. Lens Accessories: Extenders
  47. Macro Lens: Reproduction Ratio
  48. Macro Lens: Technique and Choices
  49. Fisheye: Technique and Choices
  50. Tilt Shift: Techniques and Choices
  51. Make a Lens System Choice
  52. Choosing A Portrait Lens
  53. Choosing A Sports Lens
  54. Choosing A Landscape Lens
  55. Best Lenses for You
  56. Lens Maintenance
  57. Buying and Selling Lens
  58. What is John Greengo's Favorite Lens?



I so appreciate what a good teacher John is. I wish I would have known this much about lenses when I first started out buying my lenses. It was hard finding information about lenses. I didn't want to spend money on a lens I wouldn't use. The better understanding we have about our gear the better photographers we will be. I have never seen a class like this. Invaluable...yes I bought the class! I am really impressed with the high quality photography classes available on Creative Live!

a Creativelive Student

Have loved the other John Greengo classes I've watched & purchased - and this is another winner! Having been a high school/college science teacher, it is refreshing to take a course with someone who not only is extremely experienced, seems to be a computer having stored so much knowledge, but is equally concerned about making the information truly understandable to different levels. And he shares the information using every tool he can: slides, video, interactive presentations, and great quizzes. I learned so much about my Canon lenses - and lenses in general with their many components. I am excited about testing each of mine to see what macro ratio they handle, and especially appreciated the tutorial on testing each for their specific quirk that affects super sharpness. This class is great whether you own Canon lenses or not. Thanks John Greengo!


This was a great class not just about the lenses that Canon offers but also how each lens works. As usual, John's slides are alway informative and entertaining. There is a phrase: John has a slide for that! I am not even a Canon user and found this class to have great information for the use of each specific lens. Great work John! Thank you Creative Live for another great class!