Playing around with depth of field and I think I finally get it?

Started 4 months ago | Discussions thread
Gerry Winterbourne Forum Pro • Posts: 18,619
Re: Playing around with depth of field and I think I finally get it?
3

JustUs7 wrote:

That’s a great visual. If you want to know the numbers (which focal length, which sensor, using what aperture), you can download a Depth if Field calculator app and have an understanding going into a photo what you might end up with.

What you’re seeing is that the plane of focus gets deeper the farther away your subject is.

No it doesn't: it can't because the plane is exactly what it says - a plane. Everything not at that plane is out of focus to some degree but human vision can still see things that are slightly out of focus as being sharp. It's this region of "acceptable sharpness" that gets deeper.

And the blur increases the farther you get from the plane of focus, whether in front or behind. But fall off is about 1/3rd in front and 2/3rds behind.

This is wrong too. The ratio varies from 50:50 to effectively 0:100. Look at any DOF calculator and see what the hyperfocal distance is: for wide-to-normal focal lengths it is only a few meters (let's say 20m to be generous). Focus at HFD and DOF runs from half HFD (10m in this case) to infinity. Even if we approximate infinity to 1km (1,000m) that still gives a ratio of 1:100.

Now take a longer lens (only 100mm, for example). At 10m and f/5.6 the ratio is 45:55.

Really helpful to understand when trying to take a group photo.

Yes, if you really understand it.

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Gerry
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I'm happy for anyone to edit any of my photos and display the results
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First camera 1953, first Pentax 1985, first DSLR 2006
http://www.pbase.com/gerrywinterbourne
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