Hi, i use a K7 with the FA* 300mm for wildlife, since i wanted more reach i used a Tamron 1.4 TC (which according to the popular opinion goes very well with this lens) but i never got the results i expected when pairing them together, the lens alone is tack sharp, bur adding the TC gives very unsharp images.
Trying to find out what the best combination of aperture was using the Tc i did a brickwall test with a white lens cloth as additional target (Autofocusing in Live Mode, on tripod, cable release, Iso 400 and sunny conditions, Target was about 8 meters away)
Without the TC focus was best around f 5,6 - 6,3, but with the TC even at f8 to f10 the sharpness was not quite there.
Im pretty new at this, but could the TC cause Back or Front focus? If so would the Focus tuning of the camera also affect the lens when used at its own? Or would i have to turn the Focus adjustment off when using the lens without the TC?
Here are 100% crops - non processed - jpgs 75 bit resolution (from RAW files)
First two are without TC (at f5,6 and f9,0)
Second two are with TC (at the same apertures)