[potatolicious]

I don't see a good compilation of this in the lens database, and B&H/Adorama come up surprisingly empty when it comes to K-mount teleconverters.

I'm going to be taking a nice, long, much-needed vacation soon with family, and one of the objectives is bird watching. I'm thinking about picking up the DA* 300mm for the job, but would like a bit more reach if possible.

Since all of this will be in broad daylight, the loss of a stop or two is fine by me, but optical quality is pretty darned important, as is SDM compatibility with the DA*'s.

What are my choices in this regard, and what are your experiences with the different teleconverters?

[dgaies]

There aren't too many options. I've used the Tamron 1.4x Pz-AF with decent success on the DA*300. The AF isn't as fast and sometimes takes a second try to lock, but the IQ is pretty decent overall. The Pentax 1.7x AF Adapter should also give you good results. You won't be using the SDM motor for AF, but the TC itself does the auto-focusing via the screw drive. You'll generally have to manually focus close and then the 1.7x AF-A can lock it in from there, although with the DA*300 you can usually leave it close to infinity focus and the 1.7x will be able to cover most focal distances (with the exception of close focus shots where you would need to manually move the focus ring to a closer focus position before locking in with the 1.7x AF-A.

Other than that, I think there is a Kenko 1.5x that is similar to the Tamron 1.4x, but I've never personally used it. At the end of the day, you might get equal or better IQ cropping, but I can't say for certain since I've never done a direct test to try and validate that.

[Lowell Goudge]

there is not a lot of options

the best in my view is the SMC-F 1.7x AF converter. using this gives you rough manual focus plus fine focus in AF through the moveable elements of the converter.

I use the converter on my SMC 300F4 manual focus lens and have had great success. I have had the converter since 1991

[Douglas_of_Sweden]

Optically the SMC Pentax-A 2x-S converter is marvellous. Probably applies to the corresponding 1.4x as well. Still available new from stock. But non of them are AF. But I have never seen any other converter with less degreding effects.