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03-03-2011, 04:45 PM   #1
Lowell Goudge's Avatar

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A question for Circle of Confusion Experts

Ok. I have an internal focusing lens. Brand is most likely irrelevant but for the record it's a samyang 85f1.4

At minimum focus of 1 meter it is actually about a 40 mm lens since the internal focusing is achieved by modification to the focal length. I have checked the focal length by measuring the magnification ratio .

What do you consider the DOF at F1.4 and min focus distance. Do you consider the lens to still be 85mm or the true FL of 40mm

03-04-2011, 09:54 PM   #2
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Lowell, I think the DOF will track with the effective focal length. The lens will act like a 40mm lens at the near focus mark.
03-05-2011, 05:31 AM   #3
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And that with a min. focussing distance of 1m?
Are you sure?
03-09-2011, 09:34 PM   #4
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Time for an experiment imho -- is actual dof seen at 1m what dof calculator predicts for 85mm lens or for 40mm lens? -- please let us know the results!


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