[Mohican]

I haven't seen anyone talk about this lens which is a heavyweight in the category and I believe it has its own league. Can anyone chime in how you think this duo performs?

[pepperberry farm]

what adapter are you using for this lens/body combination?

[twilhelm]

Is it even possible to adapt this lens to Pentax without a glass adapter? That would affect the performance.

[UncleVanya]

The Sony has a shorter registration distance even in A mount so it would require optical glass and likely act as a teleconverter.

[jlstrawman]

Fotodiox makes a Sony A mount to Pentax PK mount adapter, and the adapter indeed has corrective optics, which could degrade the lens performance.

[BigMackCam]

I haven't seen anyone talk about this lens which is a heavyweight in the category and I believe it has its own league. Can anyone chime in how you think this duo performs?

Fotodiox makes a Sony A mount to Pentax PK mount adapter, and the adapter indeed has corrective optics, which could degrade the lens performance.

Yes, for the very reason stated above, I wouldn't bother adapting it. You'll end up with a manual focus, optically-inferior tool (because of the adapter's optical element) with difficult-to-control aperture, if indeed the adapter offers any aperture control at all...

You'd be far, far better off considering something like the Samyang 135mm f/2. It's a high-performing manual-focusing lens, and will hold it's own with most fast 135mm models. By the time you've added the optically-corrected adapter to the Sony Sonnar, I've absolutely no doubt that the Samyang will leave it for dead (optically and operationally)

EDIT: Full disclosure, to add helpful info... In addition to Pentax I actually shoot Sony A-mount, and have a number of excellent lenses - but I don't bother trying to adapt them to K-mount for the reason given...

[willeisner]

unfortunately, this montage A sony can not be adapted to pentax,
there is a competitor of weight for this lens with excellent results
samyang 135mm f2 and superb

[Wasp]

For the last word on manual focus 135mm lenses in K mount, try this one:

SMC Pentax-A* 135mm F1.8 Reviews - A Prime Lenses - Pentax Lens Reviews & Lens Database

It has a special unobtanium lens coating, Quite a few on fleabay at the moment. Not cheap, but neither is a Sony plus adapter,

PS: For something cheaper, check out this one:

https://www.pentaxforums.com/userreviews/spiratone-135mm-f1-8-ys.html

On the whole, the Samyang is the best bet. Available new and unmolested.