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Canon Lenses: The Complete Guide

Lesson 11 of 58

Aperture: Equivalent Focal Length


Canon Lenses: The Complete Guide

Lesson 11 of 58

Aperture: Equivalent Focal Length


Lesson Info

Aperture: Equivalent Focal Length

so equivalent aperture has something that is a terminology that came around. I did not learn about this in college. This is only come around. Really. In the last five years or so, we talked about equivalent angle of view At the beginning of this class, we have a full frame camera that has a 50 millimeter lens which sees degrees on it. And in order to get that same angle of you were using the 35 millimeter lens over here, does that mean that they are identical? No, it doesn't. It means they're equivalent, which means they're very close. There's some aspects that are saying, but there are some aspects that are different when we compare a 50 and a 35. Are those the same lens? No. Do they have the same depth of field? No. They are different in those aspects will carry forward, no matter what sensor you are using them on. As an example, if we're shooting with a 50 millimeter lands on a full frame sensor, have 1.4. We're gonna get this shallow depth of field. We put a 35 on our crop frame s...

ensor. We're gonna get shallow depth of field. But the depth of field is not exactly the same because 50 millimeters exhibits a shallower depth of field because it's a longer focal length van does the 35 millimeter lens, and so they may see the same angle of view. They may be able to sit in let in the same amount of light with one point for aperture. But they are not equivalent when it comes to depth of field. And so if we were to stop the 50 millimeter down to F two, we get just a little bit more depth of field. The background is a little less blurry, and these are equivalent apertures. And so if you have a crop frame camera and you have a lens that goes down to 1.4, well, that's angle of view. That's kind of a separate issue as far as 1.4. They let in the same amount of light, yes, but the depth of field it's a little bit greater with the smaller crop frame and a little bit less with large frame. And so where this really comes into play is people who want super shallow depth of field. I want to focus on the face and have the background go way out of focus. Those folks tend to prefer working with full frame cameras because they enable us to use lenses that get even shallower depth field. And so there have been endless arguments in the forums in the chat rooms, about comparing lenses. Well, I have a crop frame camera and I have a portrait lens that is the same equivalent. It's the same angle of you. It's the same aperture, and then somebody else who owns full frame would come in and they say You don't have the same lands It's a different depth of field and they would say But I have the same angle of view and I have the same light gathering ability. But you don't have the same depth of field and they go back and forth fighting, fighting, fighting. And there's three factors, two of which are exactly the same. The angle of you is the same. The light gathering is the same one after, or that one feature is different, and that is the depth of field, and it's one off. It's not a huge deal, but just don't get caught up in the arguments in the forums. They're all sorts of thugs in there that will beat you up for saying something. Okay, so ah, 300 millimeter lands is going to see seven degrees from side to side. If you want that same angle of view on a crop friend camera, you only need a 200 millimeter. Let's so these have an equivalent angle of view. Same angle of you. They let in the same amount of light. It's both 56 but they going to exhibit a slightly different depth of field. So here's our example of our subject in focus in the background that is a little out of focus you'll see with the full frame camera. Ah, 300 millimeter lens exhibits shallower depth of field. So our trees in the background are a little bit more blurry, and at every aperture you go if you stop them both down to stop to F aid. The full frame sensor has shallow word up the field at every equivalent aperture that you said it every identical aperture that you said it at, and if you want it to get to look fairly similar, you would actually have to stop it down to F eight or so. And so roughly there is a one stop difference in the depth of field that you were getting. So if you have a crop frame camera, you're always getting about one. Stop mawr depth of field with every lens that you're shooting at when you're comparing equivalent focal wings. And so it's one of these very subtle things that a lot of people like toe beat you up on if you say it in slightly the wrong way and the wrong place, and so 50 millimeter versus a 35 same angle of you because we have different sensors. We talked about this earlier, so the same aperture, same low light ability. They're both 1.4 is both. These photographers can work in the same low light environments. They're gonna get the same angle of view, but because they're using different lenses, they're gonna have different depth of field. Same focal length. You get the same depth of field, but these are not the same focal length. So you're gonna get different depths of field. You're gonna get slightly moored up the field with the slightly less step the field with the 50 in this particular example. And so that's the equivalent aperture in the equivalent focal length that you've probably heard if you've been reading some articles about the crop frame sensor, and it's because we're using different size sensors and we've always had this issue. But it was more with 35 millimeter and medium format and large format and less people had, we're going from 35 to medium format. So it's become Maura part of the dialogue these days because, well, we have kind of a big dividing line. And we have a lot of people on both sides of the line as to why we're talking about all this different terminology, and it's a little bit hard to keep straight. And if you're still a little confused, I can understand that it is a little confusing. Go back through the material again and again, and it can, and it will eventually make sense. I certainly hope and so little break point before we go on, just to see if there's anything we need to address. Well, I think first of all, this is where my brain starts to be, like, uh, What about you guys? And like, Oh, okay, that is definitely one that I haven't had explained to me in that way before. So thank you. Um and so just Teoh push that one home. Hamburgers had asked her age. Amber's with some votes. So can you confirm that on crop sensors that the F stop of a lens is also multiplied by the crop factor so similar to what we're talking about? The example given is 55 millimeter lens at 1.8 on a 1.6 crop factor. Is that really the same as an 80 millimeter lens on F as an F 2.8 would be on a full frame? Yes, they are correct in that. And so that's exactly what you were just complaining. I wouldn't want to be careful because we're getting It's a very precise wording on Yeah, it's the equivalent look in depth of field. But it's not the same light gathering ability because they still have their good light gathering ability. I think in their example of a 1.8, because they say it's the equivalent aperture of 2.8 in the look of how much depth how much depth of field, but as far US light gathering ability, it's still the 1.8. And so if a lens says 1.8, that's what it's gathering until you hear otherwise.

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!