From: chuang@micro (Michael Chuang)
Newsgroups: rec.photo
Subject: Re: Teleconverter options (TC-16A)
Date: 2 Sep 92 17:35:29 GMT

asanders@sparta writes:

> The Nikon TC-16A is a 1.6x teleconverter that provides 
> "semi autofocus". If you manually adjust your lens til 
> things are almost sharp, the TC-16A will criticially 
> focus the lens when the shutter release is pressed half-way.
> Actually, I believe this converter has been discontinued, 
> but it can be found second-hand for around $125. The Nikon 
> System Handbook says it's a good performer.

The TC-16A is intended for use with lenses of 300 mm or shorter
with maximum apertures of at least f/2.8, I believe, though
these are of course conservative limits.  Nikon says that it
will not work in its pseudo-AF mode with the N6006, N5005 or 
the N4004/4004s (sorry, I am not sure of the non-US model
designations).  For the N8008/8008s and F4 the AF-mode switch
must be set to "C."  This is probably also true of the N2020 for which
the TC-16A was originally released.

In my experience the TC-16A is a good teleconverter.  Yesterday I
got some chromes of a green heron back from the lab.  Shot with
a straight Sigma 400/5.6 one can see the individual downy strands
of feathers on the heron's head.  With the TC-16A the down is still
distinct, though the image is almost imperceptibly softer.  Incidentally, 
I was shooting Fujichrome 50 at 1/125 with the 400 closed down to f/8 with 
an 8008s (on tripod, of course).  I have not noticed light-falloff
in the corners with the 400 mm + TC16A, though things tend to be
put in the center of the frame when using an effective 640 mm focal
length anyway.

"Moose" Peterson claims (in his _Nikon System Handbook_) that the 
TC-16A is as good as the Nikon TC-14B.  I don't have the TC-14B, so
I can't say, but he is probably right.  As with all teleconverters, 
the use of the TC-16A is to be avoided if possible, but I wouldn't
worry about its quality if it is necessary to make the shot.
However, one complaint about the TC-16A is that the bottom protrudes 
a little beyond the base of the 8008-type body - makes it difficult to 
mount on some tripods, like the Bogen hexagonal QR plate.  This is not
a problem with lenses with tripod collars, but can be minor hassle
otherwise. 

* If you buy by mail make sure they don't sell you a TC-16, which
  is designed for the defunct F3AF system.  I don't know about
  using the TC-16 just as a non-AF teleconverter.  Presumably there
  is motion of the elements in the TC-16 (there certainly is in
  the TC-16A, else it could not provide critical-AF), and the 
  converter could be in a state where you could not focus at
  infinity, for example.  I don't know how the AF was done in the
  F3AF and TC-16; it is possible that an F3AF finder is necessary
  to control the TC-16.  Anyone out there know ?

Li Du (duli@prony.colorado.edu) was kind enough to post some test
results (_Modern Photography_, 8/86) of the TC-16A:

        Resolution Test(line/mm) of TC-16A+50/1.4 vs 50/1.4(by Modern Photo.)

                  50/1.4                TC-16A+50/1.4             50/1.8AF
                  ~~~~~~                ~~~~~~~~~~~~~             ~~~~~~~~
              center  corner          center  corner          center  corner
        
        1.4     50      45              50      35              --      --
        2(1.8)  50      45              50      35              59      45
        2.8     56      50              56      40              56      50
        4       63      56              63      45              56      50
        5.6     70      63              63      50              63      56
        8       70      63              70      56              70      63
        11      63      56              63      50              70      63
        16      54      56              56      45              63      56
        22      --      --              --      --              56      50

As for non-manufacturer teleconverters, a recent issue of the British
magazine _Practical Photography_ gave high marks to the Sigma 1.4x AF.
This can be purchased for about $150 new from New York discounters.  
Lately it seems that even used TC-16A's are approaching the $200 mark.

- Mike
chuang@micro.ll.mit.edu
chuang@nmr-a.mgh.harvard.edu