Tamron teleconverter question

I just picked up a Tamron-F 2X Pz-AF BBAR MC7 Tele-converter for cheap.
Haven't put it though comparison tests, but it seems OK at first sight.

It appears to have pass-through for all electrical connections but my DA* lenses lose auto focus. Any one familiar with this tele-converter and know if/why that might be expected? Or did I get a broken item?

Unfortunately the store was an impulse stop, so I didn't have my camera there to test in advance.

The DA* lenses, on a K10/20D body utilize SDM focussing which relies on the extra 2 contacts inside the body to provide power. I doubtthat your TC has those. On other than a K10/20D body, the DA* lenses revert to normal screw drive AF.

Does your Tamron TC have the screw drive pass through? If not, that's why AF doesn't work.

Yep, it has all electrical contacts.
Well, it has the two gold tabs just around the glass which should be for the DSM. At least the only lenses I have with those that have SDM.

The tele also has the screw pass through.
Hoping I could get the screw drive to work, I tried taping over the SDM contacts but the camera then started flashing the "-MF-" symbol. So there must be some communication from the lens that says "Hey I have SDM, if the contacts are blocked give a warning".

Hmmm...so it seems the contacts are functional, perhaps just dirty?? They look clean. Everything looks clean. It is about as god as new condition as one could hope.

I have the same issue with my Sigma APO 1.4x TC. And the Sigma does have the screw drive pass through. I can only conclude that the screw drive does not marry up with the coupling on the camera body, although it does look very close from what I can make out.
Perhaps the Tamron is of a similar design.

Sorry that does not make sense What i meant was the coupling on the TC does not marry up with the screw drive on the DA* lens

My older lenses AF just fine with the screw drive. here is not even any sound. When an SDM lens is mounted, the camera is already in MF mode so no focusing is even attempted.

Went looking up the TC I found that I paid a little less than half price of the cheapest price I've seen. So not too bad. A bit disappointed, but I don't feel totally ripped off for digging in the consignment bin.

The guys in the store used to sell and even push Pentax 10 years ago. (last time I was in that store -- not quite in the neighborhood anymore) Now they know nothing about and carry a single Pentax-fit lens by Tamron. ugh!

Ayway, had to hook it up to my macro (AF works, but who relies on auto focus with macro anyway?).

I think I'll still end up having fun with the TC.
https://www.pentaxuser.com/photo/Tamron-2x-on-Tamron-90mm-Macro-997

he, he, forgot that image tags don't work.

Hmmm i must try it on one of my non * lenses and see if it will AF on those.

I'm currently loaning a Tamron 1.4x PZ AF MC4 & autofocus works perfectly on my GX10 (K10D) with the new DA 55-300...could it be anything to do with firmware perhaps? Sorry I can't be more help !!

simon

As far as I know the Tamron 1.4x MC4 is the only teleconverter atm that will work with SDM lenses on the K10D and K20D.
The previous non MC4 version will work with SDM lenses on the K10D but not the K20D.

Now why would that be? Is there more to the tele-converter than simple pass-through of the contacts? I'd think it would just be a simple wire straight through. But apparently not.

There is a massive thread about teleconverters on the other Pentax Forum.
Makes interesting reading .. if you have the time.

I have the Tamron 1.4x MC4, works fine with SDM on the K10 & K20, just hunts a bit more!

Funny thing though, just tried it with a recently acquired Sigma 100-300 F4, and (via the screw drive) focusses better with the TC on!! On it's own at 300mm it does seem as though it moves so fast that it doesn't lock on very easily at all, seems to hunt a hell of a lot. With the TC on, I'm guessing with the extra drive that it is getting slowed down a bit!

Was going to put it on eBay seeing as though some have gone recently for over £150!, but after that experience with the Sigma, it's just gone back in the bag!

That wouldn't be the one that was listed on this forum that I nearly paid £400 for until the seller got an offer he couldn't refuse was it?

he, he, tried the 2x on my 28-300 lens (not a great hunk of glass to begin with by any means). No luck auto focusing with that lens. The mechanics function but there is no way for it to lock on at f5.6 plus the two extra stops added by the converter.
The focus ring has such a short range to begin with, even manual focus is nearly impossible.

Guess that means I *need* to buy a better lens.
"Oh, honey... we need to mortgage the kids, er, no kids? OK, we need to mortgage one of your kidneys..."