Originally posted by switch79
Will the 1.4 Tamron TC work on the Pentax FA50, if so will I lose autofocus?
Will the 1.4 Tamron TC work on the 18-250, if so willi lose autofocus?
I owned a Tamron 1.4X tele-converter for a while. It was the current model with the AF coupler.
I tried it with a Pentax F 50mm f1.7. The combination does function, and will auto-focus. AF speed is reduced due to the extra drag. Image quality was pretty poor with the lens wide up to about f/5.6. From f/8 on it was better. I would expect similar results from the FA 50mm.
There are a lot of lenses in the 70-100mm class available used for a modest price. They are likely to give better results than the 50mm with a tele-converter.
I've never had a super-zoom like the Tamron 18-250mm. Due to the slow speed at the long end (something like f/6.3) it will be something like f/9.5 with the 1.4X converter. This combination will not auto-focus reliably. And super-zooms are not the best performers on the long end. It will operate with manual focus, but I would expect the results to be unsatisfactory. Again, you are better off with a used lens. Something like the manual focus SMC 300 f/4 (plain K mount) is available pretty cheap, and that would give you some extra reach. And
that lens would work pretty well with a good 1.4X converter.