Re: Macro stereo camera

[P3D John Bercovitz <bercov@xxxxxxxxxx>]

Sam wrote:
 
> By the way, the Stereo Petri is up an running, but one copal shutter is
> giving me problems. Does anybody out there have an old junker camera with a
> small copal shutter ? Where's that John Bercovitz these days ? I'll have to
> post something on the digest. Another question for John: Is the depth of
> field the same at  1:1 magnification for all focal length lenses, or does it
> narrow down with the higher focal lengths ? I'm trying to see if there is an
> advantage to MF macro. No formulas please !
 
No formulas?!  I don't get it; what's the point?
 
Sure, as long as the magnification and the f/number are the same, the depth 
of field is the same.  Of course you have to use the same criterion for the 
acceptable maximum size of the fuzzy circle for both cases or else it would 
be "unfair".  8-)  An exception to my statement would be when the lens is 
very short so its hyperfocal distance is large compared to the distance to 
the subject.  But in this case, that couldn't happen because you're saying
1:1 so the lens is halfway between the film and the subject.
 
Now that's looking at it in terms of geometrical optics; if you want to look
at physical optics too, it gets a little more complicated.  Then you have dif-
fraction effects and I should think about that before answering or else get my
spreadsheetfrom my anonymous ftp site and just try a few numbers to see what
happens.  Generally, diffraction isn't a major effect if you have a reasonably
large aperture (low f/number).
 
John B
 


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