Originally posted by conbio Maybe I need some advice and information on compatibility regarding my 1.4 teleconverter. I've been disappointed in the utility of my 1.4 teleconverter. It's terrible on the 60-250, which is almost always on the camera (K-3). Does it produce good images on any zoom? Specifically, how does the teleconverter perform on a Sigma 18-300? (I was thinking about the 18-300 for a better travel lens.)
Thanks for feedback!
i do not think any teleconverter will please you on a lens with maximum aperture at the long end of F6.3, as the loss of a stop due to the TC will make the native aperture too small for the AF system to work reliably.
you really need to be faster than F6.9 as a combined aperture to get the lens to work, and assuming the aperture is directly variable by focal length, then for lens focal lengths longer than 200mm. this is a best guess, but considering the loss of performance optically and that 200mm on the lens, plus a 1.4x TC gets you just back to 300mm (more or less) you will actually gain nothing. you are better off here to just crop in to betterframe the shot