January 19, 2016

Learn Almost Everything You Need to Know About Depth of Field Through These Great Optics Demos

Depth of field -- how well do we really understand the "distance between the nearest and farthest objects in a scene that appear acceptably sharp in an image?"

The answer to that question is usually "not a whole lot," but Filmmaker IQ's John P. Hess released the latest installment in his lens series yesterday, which helps shed some light on what depth of field is and how it works, even going further by 1.) clarifying concepts like the circle of confusion, lens equivalency, and sensors, and 2.) conducting his very own optics demonstrations so you can really get an idea of how different lens settings affect an image. Enjoy!

One aspect of the video that I found particularly helpful was the fact that Hess got really hands on -- kind of literally -- by showing us some optics demos and experiments, because for us visual learners, reading a textbook, article, or whatever, doesn't really help all that much to learn complicated concepts. Even just watching him measure the depth of field armed with but a lightbulb, magnifying glass, white background, and a ruler just makes everything seem grade school easy. (Maybe that's because it looks like a demo you'd see in grade school? I don't know -- but it was still awesome!)

Hess covers a ton of information in the almost 18-minute video, namely the many misconceptions about depth of field, depth of focus, and how all of it works. So, be sure to take notes as you watch. And if you missed the previous two videos from Hess' lens series, you can get caught up by checking out our previous post here.      

Your Comment

13 Comments

"All other factors equal - the smaller sensor will have the shallower depth of field." What a twist! I had to get out of my seat after that one. I couldn't believe it. Thanks for sharing this great informative video :D

January 19, 2016 at 10:27PM

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Alexandra
Videographer / Documentary Filmmaker
538

That's a shocker because I'm sure I've read that the opposite is true.

January 20, 2016 at 6:44AM

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Julian Richards
Film Warlord
1305

Until I wrote this video, I was one of those camera nerds that would argue on forums that sensor size played no role in depth of field - that they are the same.

I was wrong.

January 20, 2016 at 1:33PM, Edited January 20, 1:33PM

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Great effort, Thank you for the Refresher course John. To rephrase the moral of the video - "Story is on one side of the coin and the rest on the other side" :)

January 20, 2016 at 2:39AM

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Arun Meegada
Moviemaker in the Making
62

When I first took my EOS-M out, it was to Comic Con London. I thought that at f/2.0 I would have a shallow depth of field but as it was with a 22mm lens, pretty much everything in every shot was in focus.

January 20, 2016 at 6:46AM

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Julian Richards
Film Warlord
1305

"But the field of view will be different"

Of course, wider field of view always have a larger depth of field. Nothing new here.

The problem is that we often misuse the words "shallower Depth of field" in order to refer to the overall out of focus area blurriness difference between fullframe sensor and aps-c sensor.

The thing here is that here's comparing the same lens on both fullframe and aps-c sensor which is confusing. Since normally you would be comparing field of view equivalent instead. I'm sure that if you compare a 35mm on APS-C against a 50mm on a fullframe, you will get a narrow depth of field on the fullframe. But if you take that 35mm on the fullframe, the APS-C is narrower.

January 20, 2016 at 8:52AM, Edited January 20, 8:53AM

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Danny T
Photographer
454

Shallower DoF does play into the look of the Bokeh. The shallower the DoF given identical focus distance, the bigger the Bokeh bloom - ie bigger the blurriness.

Using the same lens on both cameras is representative of real world - lenses are marketed using their focal lengths - not their field of view.

January 20, 2016 at 1:31PM

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Hey John, I haven't said that you are wrong in your video. It's a very great video that only says the truth!

I only stated why it might be confusing at first the way you explain that an APS-C sensor give you a narrower dof.

And yes, given identical focus distance you are totally right.

What I'm saying is: 99% of user are often comparing field of view equivalent and not identical focal lengths on different sensor sizes. Therefor, they think that a fullframe sensor is shallower but in reality they are using a longer lens to get the same fov as with an aps-c.

January 20, 2016 at 4:34PM

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Danny T
Photographer
454

The reason why it's confusing is because we take linguistic shortcuts describing the phenomenon. We say that the larger sensor is shallower when the shallower DoF is in fact NOT coming from the sensor but the lens. To see this phenomenon we have to nullify the effects of the lens (keep everything constant) and it turns out that the opposite of what we thought is true. Then we start adding in the variables back in and we can see what's truly driving DoF.

Why does it matter? Boiler plate, because it just makes for better understanding of what's going on. A lot of people think that smaller sensors are inferior and I see a lot of lens equivalent math thrown out willy nilly (people that never shot FF and listing their lens in FF equivalent). And then there's always that nagging feeling when looking at a DoF chart and noticing the smaller sensor has shallower DoF for the same focal length, aperture and distance ;)

January 20, 2016 at 5:52PM

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Yes exactly. You said it "Dof is in fact not coming for the sensor but the lens"

January 20, 2016 at 10:07PM

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Danny T
Photographer
454

I find this tool from Canon really handy:

https://www.learn.usa.canon.com/resources/articles/Comparators/fov-compa...

It has more to do with field of view than depth of field but It gives the viewer a great visual demo on how lenses behave on different sensors..

January 20, 2016 at 8:58PM, Edited January 20, 8:58PM

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Andrew Kierans
Digital Cinema Technician
83

Digging these lens series, so interesting!

January 23, 2016 at 1:13AM

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Grace Snell
Amatuer
1

This video really nails the explanation on every level. I knew most of this stuff, but it is still refreshing to see your video demonstrate the principals involved.

BTW, the Lens Tutorial iphone app is something I often use to demonstrate these issues for people who struggle with it.
https://itunes.apple.com/us/app/lenstutorial/id500543869?mt=8

January 26, 2016 at 3:59PM

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Dave Patterson
Preditor (producer/editor)
261