V1.02
Thom Hogan’s Complete Guide to the Nikon D300
Page 381
slightly unsharp images at the extremes. But all the really long
Nikkor lenses have focus override ability, and most macro
shooters use focusing rails and manual focus for their work, so
this doesn’t become a big issue.
The other problem with getting precision in focusing is that
even a small variation in the lens itself (and its internal motor,
if it has one) can throw the system off. It’s not unusual to have
extremely small focus variations between two lenses of the
same type when used on a single camera.
Fortunately, Nikon has given us a method of dealing for
dealing with this:
AF fine tune
on the SETUP menu allows
you to test your lenses and make small adjustments so that
they all focus at the same point under the same conditions.
See “Adjusting Your Lenses” on page <395> for more details
on this.
We’re still not quite done with the technical bits. One long-
standing issue that many Nikon users don’t understand or
fully appreciate has to do with the size, shape, and detection
axes of autofocus sensors.
First, despite the markings in the viewfinder, the actual
position and shape of the autofocus sensors is different.
Matching the positions on a viewing screen with the positions
of the autofocus sensor two mirrors away can’t be done
perfectly; the manufacturing tolerance needed to do so is too
small. Each successive Nikon DSLR seems to have gotten a
little better in this respect, which shows that Nikon’s
manufacturing tolerances have improved (we’re talking about
something measured in microns here, so these are very tight
tolerances). My D300 seems as accurate as any camera I’ve
seen to date, Nikon or otherwise.
But the
shape
of the autofocus sensor markings in the
viewfinder is a little deceptive. First, there are two types of
autofocus detectors in the CAM3500DX: crossed, and line.
The inner 15 sensors are crossed and detect contrast in both
