>> Nikon used to make an AF converter called the
>> TC-16A. I've played around with one a 300mm/f4.
>> Optically the combination's OK, but the TC's
>> AF focusing accuracy isn't acceptable on long
>> lenses.
> OK I do not have the 300/f4 but I have used this
> on the 80-200/f2.8 and the Tokina 400mm. For both
> lens this TC will not AF the full distance scale-
> you must set the lens to manual focus & the body
> to S or C focus mode. Do a rough focus, touch the
> trigger to activate the AF to get the TC16A to fine
> focus.
Right. Even on a normal lens the TC-16A won't cover
the lens' entire focus range.
But what my original post was saying is that with my
longer lenses in combination with the TC-16A, autofocus
is inaccurate even if the correct focusing distance is
within the TC's range
It works OK on shorter lenses, but on both my AF
300mm/f4 and my AI 300mm/f2.8, if I carefully focus
manually so the image is dead sharp, when I press
the shutter release, the TC refocuses slightly in
front of the subject. The result is a negative
that's noticeably out of focus.
I don't know if the TC is actually causing the problem,
or if the AF system in the camera (an F5) is inaccurate,
and the combination of that TC on a longer lens just
makes it's inaccuracy more obvious.
Whatever the cause of the problem, I don't use (or
recommend) the TC-16A for long lenses -- in my opinion,
the results aren't worth printing.
I'm a picky bastard though -- lots of people act proud
of pictures that make my head hurt.
-Don
