RE: [Leica] Re: Greg Bicket's focus thread

[Dan Cardish <dcardish@microtec.net>]

Sigh.......I had forgotten that you are the guy who seems to like arguing
for the sake of arguing (did you ever resolve the UV Sonnar issue?).  

Look, at the distance I took that photograph, the AF spot in the center of
the viewfinder was tiny, and could easily have covered just the near eye,
far eye, nose, mouth, whatever.  When I look at an 8x10 print of the image,
only the near eye is sharp.  Everything else in the photograph is less
sharp.  The rear eye is less sharp.  The nose is less sharp.  The necklace
is less sharp.  Her mouth is slightly less sharp.  The shoulder is less
sharp.  He neckline is less sharp.  Everything is less sharp.  

As far as DOF goes,  all I can find readily at hand is a table in the Leica
Manual (13ed) for a 90mm lens at f4.  At 6 feet, the depth of field ranges
from 5' 10.25" to 6' 2".   For a 125mm lens, the DOF ranges from 5' 11" to
6' 1".  I assume that for a 100mm lens at 2.8, the DOF would be somewhere
in between, and probably closer to the 100mm example at f4.

I just checked a DOF calculator web page
(http://www.shuttercity.com/DOF.cfm), DOF for the 100mm lens at 6' is 3".
I think this is small enough to distinguish one eye from the other.  And if
I were only 5' away from her, which is likely based on tests I've just made
with the camera, the DOF is now only 2".  Not very large.

If I were to switch the spot to the rear eye, the camera would have
refocused itself.  It happens all the time.  I have many other examples,
unfortunately I can't post them here without fear of creating apoplexy
amongst the more conservative LUGers.  

Wasn't it Aristotle who concluded based on pure logic that heavier objects
fell faster than lighter objects?   I guess you are in fine company.

Dan C.

At 10:48 PM 05-11-00 -0500, Austin Franklin wrote:
>>  I could easily have focused on
>> the rear eye.  Why would I, though?
>
>Er, that's the point, I don't believe you couldn't have 'easily' focused on 
>the rear eye...any autofocus camera can focus on the face...and with a DOF 
>of 2.8, it really hides exactly where it focused anyway...unless someone 
>wants to reverse calculate it...
>
>I don't think that image helped either way in the discussion...
>
>
>