Other optical equipment
Other optical equipment
On this page optical eqipment that does not fall in any lens category or that has some special features will be presented. As a starting point the TC-16A teleconverter is presented here.
There was once a teleconverter in the Nikon lineup that should offer a very special feature on the way from manual to autofocus cameras at the end of the 1980’s. With the help of the 1,6x converter TC-16A photographers should be able to enjoy limited autofocus with older manual lenses. Limited in that sense, that the lens group inside the converter is able to travel a limited distance back and forth, operated by the traditional screwdriver-AF. This in turn leads to a reduced focus range around any given focus distance, which is pre-set on the manual lens. The focus range of the converter is depending on the focal length of the lens used. To put is simple: The longer the lens, the smaller the focus range. The operating manual lists the focus range for lenses focused to infinity as follows (excerpt):
6mm: inf. – 0,2m
24mm: inf. – 0,33m
50mm: inf – 1,2m
100mm: inf – 4m
200mm: inf. – 16m
300mm: inf. – 35m
For whatever reason, Nikon decided to provide an electrical interface that is different from any other autofocus lens. Therefore this converter is only compatible with very few cameras that are programmed to recognize this TC. It is compatible with F501, F801, F801s, F90, F90x, F4, F5 and F6. The only digital cameras compatible are the D2h/s and D2x/s. As a result the TC-16A DOES NOT work on D100-D300s, D700, D800, D1/h/x, D3/s/x or D4. It is expected that it will not work with newer cameras any more.
Fortunately some people have found a way to modify the pin-layout of the electrical contacts resulting in a converter that behaves like any other autofocus lens, making in compatible with all modern cameras. If you search on the internet for the conversion instructions you will see, that this is not the simplest mod. It even includes the movement of one contact pin. I admit that I would be interested to do this modification myself, but this time I got a bit lazy and bought an already converted TC-16A from a seller on ebay who seems to do this conversion on a regular basis. Besides moving one connector pin to another location a chip from a 70-210mm lens has been integrated into the converter. Therefore the pictures taken all report the 70-210mm f/4 lens in the EXIF data.
My initial tests of this converter were performed on a D700 in combination with the 400mm 3,5 IF-ED. The manual lists only lenses up to 300mm as compatible, but the 400mm lens still works very comfortably with the TC. I can imagine that above 300mm and depending on the TC lens setting a higher degree of vignetting can be seen. An aperture of 2,8 or brighter is recommended by the manual due to limitations by the autofocus capabilities of contemporary cameras. With more modern cameras the limitations can be liftet a bit. The focus at an effective aperture of f/5,6 (400mm 3,5 with minus 1,3 stops due to the converter) is working very well on the D700.
Reports about the optical performance vary widely. Many people complain about falloff in brightness and sharpness towards the edges of the frame while the center offers a very good resolution. During my testing with the D700 and 400mm 3,5 setup I could not verify this – to the contrary! The results were very good overall and the 400mm 3,5 seems to work very well with this converter. Sharpness in the center is already acceptable at f/4 combined with prominent vignetting. Stopping the lens down to f/5,6 increases the contrast and vignetting becomes a non-issue. Contrary to my expectations the TC-16A is almost as good as the TC-14B, at least it is not far off.
From a handling perspective the converter provides a quick focus experience – as long as the lens is set to a distance close enough to ideal focus. At longer distances the range of focus is quite comfortable, the closer it gets the more precisely has to be pre-focused. The focus speed equates to that of an average screwdriver lens. Summing it all up I am quite satisfied with the performance of the TC-16A. It turns the 400mm 3,5 IF-ED into a 640mm 5,6. Stopped down once it becomes a very good 650mm f/8 lens with autofocus. It is a pity that Nikon dropped this concept rather quickly. A range of AF converters with different magnification ratios would have been very welcome. The TC-16A provides a useful AF experience even on lenses out of its designed range of up to 300mm.