Originally posted by funkythiru If the teleconverter covered the ff sensor would vignetting be negated?
Using a crop-sensor lens with a FF teleconverter could reduce or eliminate vignetting entirely depending on the lens. I just tried the 10-17 FE lens on the K1 with a 1.7 FF TC. No vignetting visible in the viewfinder even at 10mm. Have not tried a picture though.
On the K1 you can choose FF mode or Crop mode or auto mode where the camera will choose the mode depending on the lens connected.
Note that "crop-sensor" lens is not a definitive description. A number of crop-sensor lenses produced by pentax do in fact cover the FF sensor with no or very little vignetting.
What exactly are you trying to achieve ?