Re: [OM] DoF Compared

[Chuck Norcutt]

As accurate as one can get still doesn't tell me anything.  If nothing 
else I don't have any idea if the camera and/or lenses can even resolve 
to the difference I've been talking about.  But if live view allows you 
to distinguish between two high contrast targets at 5 and 5.5 meters or 
even between 5 and 6 meters apart using both lenses at their wide open 
aperture at 24mm I'm more than happy to accept the experimental result.

The only required test it to set up the two targets at the appropriate 
distances and say yes or no, I can or can not clearly shift focus from 
one to the other and back again.  I think it's questionable but that's 
just a guess.  I could be completely wrong and would prefer to be.  It 
would be nice to know that one can actually focus that accurately at 
that distance.

Chuck Norcutt


usher99@xxxxxxx wrote:
>  "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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