Originally posted by PentaJP So I assume you can use a teleconverter with A-50 f/1.7 and get decent results as long as you can identify a TC which works fine with it. Sorry, I am not really helping here.
Well, that is the general picture anyway. One lens+tc combo may work and another one not.
So, it is of interest but not of relevance to report the experience with one combo, if another one is under discussion. Even slight variations in the lens design (like a couple of millimeters more or less distance of the rear element to the mount) will visibly influence the performance of a tc combination.
In the film days there were several genral rules repeated all over about the use of tcs:
- never use a tc with a wide angle lens. Firstly, it doesn't make much sense, as one would have usually covered the resulting fl anyway with another lens. Secondly, wide angle lenses often are not telecentric and that's bad for a tc.
- never use a tc with slow zooms or consumer grade zooms - the image degradation will be too obvious and anyway the resulting combination is too slow to be useful, except in rare circumstances.
- cheap tcs usually will not provide high IQ.
- tcs are meant to be combined with the longest lens in your portfolio, to give that extra reach.
- and then there are some (more or less) dedicated tcs, which work well with one or a few select lenses (like the Sigma tcs, the old Vivitar tc for the 70-210/3.8 zoom or the Pentax L tcs)
In my own experience, I feel, this rules generally true, though some exceptions may apply in real life.
Ben