Originally posted by goldenarrow Is there a model # for the Tamron 1.4?? It might be "good enough" for my needs.
Not sure what your needs are....
But the Tamron does not modify any data from the lens, so the body doesn't know there is a 1.4X TC between it and the lens. For example, when the lens is set at 200mm FL, the effective FL is 280mm, but the body still thinks the FL is 200mm. When you use the body to set the aperture at F/4, the effective aperture is F/5.6.
Also, in my experience, when the DA* zoom lens is at the long end of the FL (there is no reason to use the TC at the short end of the FL), the autofocus of the body most times keeps hunting back and forth as if it can't decide where to lock focus on. When you remove the finger from the shutter release half press, and then half press again, the focus may lock. It is annoying and I can't really call that "working."
The symptom is the same with the DA* zoom lenses I have: 16-50, 50-135, and 60-250.
I personally prefer the Pentax 1.7X AFA. I haven't used the Tamron 1.4X since I got the Pentax 1.7X.