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Thread started 27 Jun 2013 (Thursday) 13:35
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Focal Length in Relation to DOF

 
Stillwater ­ Gold
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Jun 27, 2013 13:35 |  #1

How does focal length relate to DOF?

Pete




  
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maverick75
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Jun 27, 2013 13:37 |  #2

DOF will decrease the longer your lens gets, but don't forget it's still affected by the aperture and your distance from the subject.


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SkipD
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Jun 27, 2013 13:37 |  #3

Use this on-line depth of field calculator (external link) to experiment a bit with the variables.


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gonzogolf
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Jun 27, 2013 13:48 |  #4

Use the calculator that skip linked to. Rule of thumb, longer lens is less DOF, Closer to the subject, is less DOF.




  
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Stillwater ­ Gold
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Jun 27, 2013 14:07 as a reply to  @ gonzogolf's post |  #5

What I'm finding is the DOF is the same given the same f stop and different focal lengths...what's different is the magnification factor. The longer focal length will magnify a distant object from the focal point and show less of it thus isolating your focal subject more from the background.

Pete




  
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TeamSpeed
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Jun 27, 2013 14:15 |  #6

Same fstops, same distance to subject but different focal lengths will NOT yield the same DOF.

Little example I did a long time ago, using DOF calculation results to put a picture to the math (hopefully very accurate):

IMAGE: http://teamspeed.smugmug.com/Electronics/Reference-Material/i-VDMSFhL/0/O/DOF_combinedset2.jpg

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JWdlft
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Jun 27, 2013 14:21 as a reply to  @ TeamSpeed's post |  #7

On that page, to the left, you'll find a link to 'online depth of field table'. The table shows DOF at different distances/apertures per focal length so it's easier to see the effect each factor has.




  
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gabebalazs
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Jun 27, 2013 14:24 |  #8

TeamSpeed wrote in post #16070347 (external link)
Same fstops, same distance to subject but different focal lengths will NOT yield the same DOF.

Little example I did a long time ago, using DOF calculation results to put a picture to the math (hopefully very accurate):

QUOTED IMAGE

great find TeamSpeed!


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TeamSpeed
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Jun 27, 2013 14:25 |  #9

Thanks, it took a while to put it together, and I think I lost my original PSD file. :(


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Stillwater ­ Gold
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Jun 27, 2013 15:03 as a reply to  @ TeamSpeed's post |  #10

That's great TeamSpeed...I was hoping to find an answer that didn't use up so many brain cells...as I get older & older I'm finding more and more a of a limited stock of useable cells.;) Thanks.

Pete




  
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Jun 27, 2013 22:11 |  #11

Try framing the subject the same using the same aperture:
FF sensor F2.8 50mm at 5ft total DOF .5ft
FF sensor F2.8 100mm at 10ft total DOF .5ft


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Focal Length in Relation to DOF
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