[OM] DoF Compared

[usher99]

 "But if you tell me that you can *crisply* delineate
focus at 5 meters vs. 5.5 or even 6 meters using live view I'll agree
that the focusing part of my objection is moot.  But that still leaves
the performance of the lenses at f/4."

Chuck Norcutt


I think 10X live view on a tripod is about as accurate  in focusing as 
one can get w/o a ton of bracketing and comparing like DXO does.
A meter stick at a known angle at the focal plane might answer how much 
play is in the focusing.

Mot sure how one separates performance per say from apparent or actual 
differences in dof.  Some lenses as they  are stopped down do not
symmetrically add distance equally to the near limit and far limit of 
the dof (as "ideal" lenses do used in the usual geometric model 
calculations) ---some just add to the far limit.  ?focus shift? This 
could happen
with the same MTF performance.   So a similar experiment looking into 
the near limit of dof could be evaluated with different findings.
Aberrations in the lenses and color predominance of the scene could 
alter results too so it may be near impossible to dissect
out "performance" differences in the lens from changes in perceived or 
real dof due to other lens design characteristics..

In any event I am impressed with AG---defined an interesting 
theoretical /practical issue, attempted a reasonable experimental 
approach to
investigate, performed the experiment and then posted it  (with crops 
even ) for our comments.  Thanks.

Mike
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