Re: Focusing

["Willem-Jan Markerink" <w.j.markerink@xxxxx>]

On 27 Sep 96 at 21:06, Bobbie Doyle wrote:

>       If Konica peaks at 750nm and Kodak extends to 900. Would Konica be
> as sensitive to focusing as Kodak? My lens does not have an IR mark, so
> when I focus I slightly compensate toward the closer distance, (hope I've
> been doing that right)! Would the Konica be more forgiving since it does
> not extend as far?  In other words, should I treat the Konica the same as
> I would Kodak in regard to focusing.
> 
> Bobbi

In general the Konica is less sensitive to this focus error....but 
keep in mind this also depends on the filter used: an opaque #87 with 
Konica might result in more error than the Kodak with a #25.
Another proof for the difference: the Konica Hexar AF system can be adjusted 
for IR-focus, both a '750nm' setting and a '850nm' setting.... 

As an aside, about APO: I noticed that the explanaining chart used
by Mamiya doesn't exceed 750nm....while on the other hand Leica
specifically says that their new APO lenses are corrected up to the
near-IR. Hence no definition of APO....;-((

As an aside 2: while you can correct focus on b&w film, since it only 
uses part of the spectrum, you cannot as easily correct for 
Ektachrome IR. If you shoot this film wide open, your image quality 
will improve only by using APS lenses....
--
Bye,

       _/      _/       _/_/_/_/_/       _/_/_/_/_/
     _/  _/  _/               _/       _/  _/  _/
     _/  _/ illem    _/     _/ an    _/  _/  _/ arkerink
                     _/_/_/  



      The desire to understand 
is sometimes far less intelligent than
     the inability to understand


<w.j.markerink@xxxxx>
[note: 'a-one' & 'en-el'!]

------------------------------

Topic No. 6