[WPRESTO]

I dug out my own test of the 150~450mm without & with the 1.4XTC. I was using a K3 as the K1 was not yet available. I will not go through all the conditions of the test except to say I took extraordinary measures to insure that only differences in optical performance were recorded, no vibration, no focusing error. Taken at f8 on the presumption that would probably give the best possible IQ.
There is the original shot followed by a crop of the central set of bars followed by a deeper crop of the interior set of bars. Each set of three is from the same image file, the only PP was a minor tweak to make the exposures as nearly identical as possible. The lens + TC does appear to resolve more detail, especially visible comparing the third and sixth test images.

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[mikeSF]

Going to a wildlife photo tour.
I am thinking of this setup: K-1 II with a Pentax 150-450mm + Pentax 1.4 convertor
Is anyone has experience with this setup?
I know the convertor will create black corners.
Is there in the Market any modern convertor for full frame with AF and contacts?
Thanks
Gérard

You should definitely do some testing with your specific gear, but in my case using the 150-450 with a Tamron 1.4 X teleconverter on the k-3 II, it is always better to use the teleconverter than to crop the image. Check it out for yourself before you take anybody else's word for it.

[swanlefitte]

A test I like to see is before the lens starts falling off at the long end with the tc vs the lens at the long end with equivalent fstop. Because if the tc can take advantage of the sweetspot it helps. Yet you lose a stop which if stopping down the lens you gain an advantage. Play both to their strengths.
I speculated that on my 55-300 plm the tc is worth about 1.28x I think.