TC-16A Focusing range

[Kim Pilegaard]

I have a TC-16A modified for modern cameras by Erik Lund. I wonder how to calculate the focusing range for a given lens and a given preset distance on the lens. In the original manual there is a table giving focusing range with the lens set at infinity for different lenses and an illustration showing an example of shifting the focus setting for a 50 mm lens. However, it should be possible to find a formula to calculate this for any given lens and any given preset distance?

Yesterday, I tried it on my Telyt 560/6.8 and it performed surprisingly well.

[Erik Lund]

Very tricky I think, especially if considering designs with CRC and floating elements,,, The performance is most likely optimised for infinity for the TC to work the best,,, so focus closer 'as little as possible' would be my guess,,,

[Kim Pilegaard]

Maybe it is difficult, and of course I can just try it out. For the 560 mm, the focusing range would roughly be from infinity to 118 m (by a rough extrapolation from the table in the manual). The near limit seems to scale with the square of the focal length.