Originally posted by jatrax I do not understand this comment, or perhaps you have miss-read all of the other comments. The K-70 has no problem at all with the 1.4x TC. However, using it with slow consumer zooms like the 70-300 or the 55-300 is going to be a problem. For example I have used the Pentax HD 1.4x TC on my DA*60-250 with very good success. Note that this lens is constant f/4 so the TC makes it f/5.6 and auto-focus works fine.
Mostly the 1.4x TC lives on my DA 100mm f/2.8 macro giving me a 140mm f/4 macro lens.
Thanks, jatrax , for your comment. I should have mentioned the following link:
HD PENTAX-DA AF REAR CONVERTER 1.4X AW / Converter / AF Lens Adapter / K-mount Lenses / Lenses / Products | RICOH IMAGING
That link is the one available from Ricoh for 1,4X TC. The document is unclear or not updated, because it does not make any reference to K-70/KP. Please, see footnote about "
AF support confirmed models". At the bottom it can be read 2017.
I understand that 55-300 PLM f6.3 works with limited number of bodies, assuming their firmwares were updated. Not only that: the f/6.3 makes a difficult focusing in low light conditions, so, it is worsened with 1,4X TC and not recommended to use with it
The above document refers on compatibility with lenses up to April 2015, so it does not mention 55-300 PLM, but after reading the limited performance of
DA 55-300mmF4-5.8ED W in Phase-matching, we can assume that performance of 55-300 F6.3 PLM is going to be even worse.