Like Sandy mentioned putting it on the Kp, K3, K3ii, K70, etc. will get 24mp into the crop zone of the lens which is more than the 16mp in the crop zone you get from the K1 in crop mode - allowing for higher detail when you need reach. It is likely that the DA 1.4x would work both in K1 crop mode and on the crop cameras without limitations but I don't have any direct evidence of this.
---------- Post added 03-22-19 at 11:07 AM ----------
Originally posted by JensE I'm afraid it's the
only combination which keeps Shake Reduction working correctly - no other converter out there seems to convert the focal length reported by the lens. I don't own that combo, but there have been
several posts about the amount of vignetting, which is to be expected. It wasn't entirely limited to the APS-C image, but also not covering the K-1 sensor completely. The newest, relatively speaking, Kenko 1.5x (I use the Pz-AF 1.5X TELEPLUS SHQ, but with a Sigma HSM OS lens) and Tamron 1.4x converters, which have all the necessary contacts, should work, but will cause the SR to under-compensate.
While this is true of the AF TC's the 1.4x-S and 2x-S manual focus converters (A series or not) will not transmit the SR data and allow the body to be set to whatever SR value you want - if manual focus is sufficient.
My past experiments using the 1.4x-S vs. the DA 1.4x lead me to think the 1.4x-S A version is very close to the same performance at least with my FA* 300 f4.5 used on a K-3.
The 1.4x-S should also cover the FF sensor without problems.