there are three issues with respect to sigma TCs.
one issue is mechanical, one electrical, the other is optical. the mechanical issue is that sigma TCs have a somewhat proud or forward extending front element, that requires a circular recess in the rear of the lens roughly 35mm in diameter, and a minimum of 12mm deep.
Many lenses do not have this type of recessed rear element or rear barrel inner diameter, and the TC simply does not fit.
Other lenses , like the BIGMA (i;e sigma 50-500) have a focal length restriction, as at 50mm the rear element hits the TC and therefore there is a restricted focal length on the bigma. the electrical issue is in 2 parts, first, sigma TCs for pentax are not HSM compatible, so if your lens is HSM forget it, you have MF only. Second, the TC feeds lens data unmodified, and therefore your aperture is not correctly reported, which is OK but can lead to the need for exposure compensation, and it also messes up P-TTL flash the optical issue is that on any camera for the AF to work reliably you need a maximum aperture of F6.7 or larger, and therefore the AF does not work with either the 1.4x or your 2x TC (Or any other TC for that matter)
I am not sure whether the TC can be mounted to your lens, but if it can you are limited to a dark viewfinder to focus with manually
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