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**Lowell Goudge** · 03-03-2011, 04:45 PM

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

**Canada_Rockies** · 03-04-2011, 09:54 PM

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.

blende8 · 03-05-2011, 05:31 AM

40mm?

And that with a min. focussing distance of 1m?
Are you sure?

rhodopsin · 03-09-2011, 09:34 PM

aka 'breathing lens' (

)

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!

03-03-2011, 04:45 PM	#1
Lowell Goudge Site Supporter Join Date: Jan 2007 Location: Toronto Photos: Gallery \| Albums Posts: 17,892	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

03-09-2011, 09:34 PM	#4
rhodopsin Veteran Member Join Date: Dec 2009 Location: Deep Forest Posts: 643	aka 'breathing lens' () 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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03-04-2011, 09:54 PM	#2
Canada_Rockies Loyal Site Supporter Join Date: Nov 2007 Location: Sparwood, BC, Canada Photos: Gallery \| Albums Posts: 12,385	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
blende8 Veteran Member Join Date: Feb 2007 Location: Bremen, Germany Photos: Albums Posts: 1,521	40mm? And that with a min. focussing distance of 1m? Are you sure?

A question for Circle of Confusion Experts

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