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Canon Lenses: The Complete Guide

Lesson 13 of 58

Aperture: Maximum Sharpness


Canon Lenses: The Complete Guide

Lesson 13 of 58

Aperture: Maximum Sharpness


Lesson Info

Aperture: Maximum Sharpness

maximum sharpness, trying to get the sharpest possible pictures with our lenses. And so we always want to get sharp pictures. The theory is, lenses should be optically perfect. Win shot wide open. That's that's the theory. But let's check reality. Reality is, is they're not OK on. The problem is, is there's imperfections that are disguised and hidden by stopping the lens down. So you may have a 1.2 lens. If you stop it down to two or to eight, it's gonna get sharper, all right, until a certain point, okay? And so, ideally, they would be perfectly sharp, wide open, but they're not. And there's a reason for that. And it's called the fraction all right, and it has to do with the way light works. And we're not going to do a full physics physics class here on you, But we're gonna talk a little bit about the way light works. Diffraction is light scatter as a result of passing through an opening. Okay, so we have our lands lights coming through the lens. We're gonna close our aperture down to...

a fairly small opening, and his light goes through that lens. It hits the edges of those blades, and it gets redirected just a little bit. Okay, you can imagine throwing a baseball, and it just nicks the edge of the wall and it changes direction. That's what happens to the light. And so when Light is supposed to be going straight, it gets slightly deflected, and that's gonna cause a little bit of loss of sharpness. And this happens mawr. The smaller you go, the smaller that opening this. And so the question is, is what's the best aperture that I should shoot at? So let's take a look at a sample shot that I wanted to shoot to see what is the sharpest aperture with this particular lens. What I did is I blew up small sections from the center of the photograph as well as the edge of the photograph, and I shot this several times from 1.42 F 22 you can look at these images and judge for yourself. Which aperture yields the sharpest photographs and which ones are the blurry ist now, Depending on what sort of screen you're looking at, you may not be able to see it if you have a small phone that you're looking at this with. But I can tell you right now that 1. does not look very sharp. There's a lot of problems with this lands, especially on this little tiny camera lens, which is so bad for two reasons. Number one lenses air not perfect when they're shot wide open at 1.4 in this case, and secondly, this sample is from the extreme edge of the frame. Lenses tend to be sharper in the middle and softer over on the side. And so everything on the bottom row, I would say, is going to be less sharp than on the top row because it's from the edge of the frame. But looking at this, if I go all the way out to F 22 it's not quite a sharp, and it's because of diffraction. Around 5.6 on this lands is where this lens is the sharpest. Now, the way that you can figure out where your lenses the sharpest is one to test it and just see what works for you. But a good general idea rule of thumb is that the sharpest apertures are in the middle of the range, so figure out the range. If it's 1.4 to it's gonna be around 5.6. If your lenses Ford F is gonna probably be around F All right, so with a full frame sensor and a 1.4 lens, you're gonna have imperfections that are going to get reduced as you go to to and to eight NF four. And by the time you're at four and 56 you're looking at really good sharpness from that particular lands. And if you put that same lens on a crop frame camera, it's the same lens. It's gonna act exactly the same way. Those imperfections are going to disappear at the same rate, and they're going to be equally sharp here. But this is where things change up a little bit because of diffraction, and so diffraction gets worse as we go F 11 16 20 to and on the crop frame sensor that that diffraction zone changes sooner than it does on the full free. What's different about it? We have the same lens mounted on these two. What's deferred is the sensor, and it's not the sensor size. Even though I have different size sensors here, it's the pixels on the sensors, and so diffraction is impacted by the pixel size, not the sensor size. So here's what's going on pixel level in your camera. All right, so this top example is for a full frame camera. Let's just look at a group of pixels nine in this case on the bottom one, because they tend to have smaller pixels and more pixels crammed in a smaller area. They have smaller size pixels. Okay, now the circle in the middle indicates a point of light that we're focusing on. And as we change, our aperture from 1.4 to 1 point to this point of light slightly grows because of diffraction, but it hasn't grown very much. It's still very much on one dot here. It's very much on one's one pixel here, but it's slightly overlapping into its neighboring pixels. And if it starts overlapping too much, that's when we start noticing a loss in sharpness and we go to F 2.8. It grows ever so slightly, but we're still improving problems with lens, and that's kind of having the greatest impact as to why we're getting sharper, so we get down to 5.6 and this is where our lands is really doing well. It's at its sharpest. But as we get down to F eight notice in the lower example, what's going on? That circle is now encompassing not only the square in the middle, but ah lot of the nearby squares next door, which is causing a loss of sharpness because that one point of light needs to go toe one pixel, not nine pixels, that causes blurriness. And so the smaller your pixels, the sooner this diffraction starts off, and the further you go, the worse it gets, the smaller your pixels. And so if you have one of the very compact cameras the point and shoot cameras that has 20 megapixels on it, you're going to hit that diffraction price, perhaps at F 456 depending on the size of those pixels. And if we stop our leads all the way down to F yes, we're gonna have a fair bit of diffraction on our full frame camera. But our camera that has more densely packed pixels is gonna have even mawr diffraction And so the prime place that you set your lens depends on the lens itself and the camera and how many pixels and what size those pixels are. And there's some people that would probably like me to geek out for the next hour on diffraction, and we're not gonna do it. We're only going to take it so far, folks, but I just I need you to be aware of. You don't want to be over here. If you're trying to get the sharpest point in your lands and you don't want to be down here, do I shoot it F 32. Do I shoot it? F 1.4? Absolutely, yes, it's absolutely necessary in certain types of photography. The reason this is handy information is that you don't go there if you don't need Teoh and the more you know about when you need it and when you don't need it. This is good, helpful information. So if you don't need F 32 don't set F 32 F 22 is better, and that's same with 16 and 11 and eight so kind of my default steadiness. Well, I would prefer that my lens be said it f eight and I will change it if and when necessary. Now, if you would like a home study project because there's just only so far we're gonna go in this class, I'm gonna give you three terms here and you can go look these up and you can study these and you can read the Wikipedia page. And you can google this and find all sorts of photographers that like to write white papers at ad nauseum about details of pixel size, the airy disc and my favorite, the circle of confusion, which I always thought surrounded me. But apparently it has something to do with the size of light as it's focused through your lands. And so all of this will impact the diffraction and the sharpness of your images. And perhaps someday I will even take this further and go into this area. But I want to give you a little bit of something extra that you guys can go into on your own

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!