Darkroom Digest: Understanding & Calculating Relative Depth of Field

September 21, 2016  •  2 Comments

Have you ever wanted to compare the depth of field of two different lenses? 

I am going to share a very simple formula with you in this article that will help you understand the relative depth of field between two lenses.  For example, you may want to know the relative depth of field between two lenses at portrait distance.

The formula is simple: Relative Depth of Field = (f1/f2)2.  Where f1 is lens one, and f2 is lens 2.  

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Let's work through an example.  A 50mm lens compared to a 300mm lens would be (300/50)2 = 36.  This means the relative depth of field for a 50mm lens is 36 times greater than a 300mm lens at the same aperture and distance.  The key is understanding that we are making these calculations for the same aperture and distance.  

Remember the time when lens makers put the depth of field scales directly on the lens?  I think this is why I love the older film small format cameras.  I loved the old lenses because I knew the hyperlocal distance at a glance (closest distance that appears sharp when the lens is focused at infinity).  

Give this a try in your style of photography and then let me know how you are applying this knowledge to your style and genre.    

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Tim Layton Fine Art
Hey Jim, good to hear from you. You are correct!! My new auto-correct has gotten me two days in a row! Thanks for the heads up.
"(closest distance that appears share when the lens is focused at infinity)." I think you meant "sharp".

Glad your posting more articles. I check in every couple of days.
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