RE: Nikon Autofocus Lenses

[Theo Benson <TBenson@xxxxxxxxxxxxx>]

Dena:
I use several Nikons and both D and non-D lenses with Kodak IR film. It has
always puzzled me why Nikon chose to ignore IR in the newer "autofocus"
lenses (I'm also furious about them abandoning hyperfocal markings, but
that's another complaint...) I guess they figured that not enough people
shoot IR to bother with the infinitesimally small additional production cost
of adding a small red dot (the horror!). There is indeed no IR index mark.
Internal focusing has only to do with how the individual elements are moved
to achieve optimum focus. It does not change the fact that the focus is
calculated by the camera for visible light subjects.

There are two main ways to compensate for the visible/IR focus differences.
First, you can shoot a series of images at various distances with each lens
you are going to use; manually bracket either side of the "suggested focus"
and determine which one was the sharpest (tedious). This will tell you the
correction factor needed for IR, and you can then (oh so carefully) place a
small white dot of paint or "liquid paper" on the lens as an IR reference
mark. Using this mark, focus manually when using IR. The second choice (and
my favorite) is to shoot at very small apertures (f11 or f16 -- that's small
for us 35mm crowd) to give a broad enough depth of field to include the
actual optimum IR focus for your subject.

One last note for Nikon users: do NOT shoot IR with any of the data backs on
your camera body. Even when they are "turned off," the small mirrored
surface on the LCD matrix in the data back reflects some of the IR that
passes through the film BACK onto the film, leaving a small bright rectangle
in each frame!

Hope this helps!

Theo Benson, M.A.
Theo Benson Photography

Visit the Redwood Empire Group to view some of my Egyptian images:
http://www.sonic.net/~rod/images/

> -----Original Message-----
> From:	Dena Thompson [SMTP:denamt@xxxxxxxxxxxxx]
> Sent:	Sunday, July 12, 1998 10:42 AM
> To:	infrared@xxxxx
> Subject:	Nikon Autofocus Lenses
> 
> I apologize for the redundancy of this question, but I'm having
> difficulty finding information on IR correction for Nikon autofocus
> lenses. I've just purchased the Nikkor 105 Micro lens and a Nikon N70.
> (I'm ususally a large format shooter). Since the "D" series lenses
> utilize "internal focusing," does this eliminate correction for the IR
> spectrum? Also, the lens does not have a red dot indicator for IR. 
> 
> I'd appreciate any info, since I can't seem to find the mention of IR in
> any of the Nikon literature.
> 
> -D. Thompson
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End of Infrared-Digest V0 #676
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