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Re: [OM] OM macro / closeups vs medium format / TLR

Subject: Re: [OM] OM macro / closeups vs medium format / TLR
From: frieder.faig@xxxxxxxxxxxxxxxxxxxxxxxxx
Date: Thu, 3 Jan 2002 14:45:17 +0100
On Tue, Jan 01, 2002 at 05:37:34PM +0000, John A. Lind wrote:
> At 15:54 1/1/02, Frieder Faig wrote:
> 
> This is difficult to convey in print.  Perhaps some graphics will show it 
> better.  Some time ago I put together a spreadsheet to get a feel for how 
> all this works. 

The same, what I´ve done. Just needed some research on my PC  to find.

> Also created some graphs to show the significant 
> results.  I've exported these charts to image files and put them into a web 
> page with a little text to explain them.  This page is *unlinked* and 
> stands alone on my site (you gotta use this URL):
>    http://johnlind.tripod.com/science/sciencedof.html
> At some point in the future this page will likely get integrated somehow 
> into the rest of the information about lenses.

Good site. Must have been lot of work. I like it.
To be very accurate. Ouer opinions are not opposed to each other.
 You`ve chosen 1:10 magnification to demonstrate that dof remains practicaly the
same. This is true, but only with high magnification like you used.

I´vs found a ugly hyperbola curve for dof depending on focal length.
I´ve some graphics too. have a lock at:

http://studweb.studserv.uni-stuttgart.de/studweb/users/mas/mas12462/Optik/dof_considerations.html

oh, oh, the urls are getting longer and longer...

Frieder Faig

 
> The confusion (pun intended) may be about my comments regarding the effect 
> shifting to a larger film format has on DOF.  If I change from my OM-1n 
> with 50mm lens to my M645 with an 80mm lens and use the same aperture and 
> focus distance, the depth of the DOF shrinks slightly.  While the field of 
> view has not effectively changed, nor has the size of the subject (at 
> critical focus distance) in the viewfinder changed, but magnification 
> _on_film_ has changed.  Why?  I'm now filling the same percentage of a 
> larger piece of film with the subject.  In order to "fill" a larger piece 
> of film with the subject material, the magnification on film *must* 
> increase.  That's why the focal length increased to maintain the same field 
> of view and perspective.  One might think an allowable increase in the 
> maximum acceptable circle of confusion diameter for the larger film format 
> would compensate.  Less enlargement is required for same size print or 
> projection.  It does, but not completely.  DOF shrinkage occurs at (focal 
> length)^2 and DOF growth occurs at (max acceptable CoC)^1.  However, both 
> focal length and CoC growth are linearly increased with the increase in 
> film format.  This leaves a (focal length)^1 shrinkage in DOF.  Think of it 
> as two steps backward (focal length) and then one step forward (CofC).


I totally agree 1000 0.000000e+00re with you.

Frieder Faig


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