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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