Originally posted by rtwpaul so as the title suggests - teleconverter help - which brand works with the SMC Pentax-DA 18-135mm WR
I am traveling on a motorcycle and don't have space for a large selection of lenses (sadly) so looking at this option. Prices are all over the place and it seems like some (non pentax) brands fail to work 100% of the time.
Any experience/ suggestions?
The Tamron F 1.4X teleconverter, not being made, had the original Pentax FA lens series power zoom contacts, and the screw slot AF mechanical linkage, in addition to the A and F(A) lens information transfer contacts: with its up focal length, loss of one f stop at the rated widest aperture of original lens, features. I picked one up for $100 from a midwestern camera store chain on line a couple of years ago (since the full frame DSLR came out its price seems to be between $150 and $500, when and if located for sale). It covers APS-C and full frame formats; it works with both in lens powered motor focusing zooms (which took over its FA power zoom contacts use after the original FA zoom lenses were discontinued by Pentax), and the screw type slot linkage autofocus lenses, or zooms, or, converts the focal length factor for MF lenses which need no electrical contact information or motor power, or old power zoom linkage. I have the Pentax 1.4 A-S, 2X A-S (which carry lens information, but offer neither kind of AF linkage), two Sigma 1.4X converters (which offer only the screw type AF linkages, without the in lens motor powering contacts AF linkage), and the Tamron F mentioned.
If you look on the Forum, under third party lenses, somewhere at the bottom it reviews all teleconverters of legacy use with the K mount. There are two Tamrons, one the F series, which can work with all PKAF lenses made. No other teleconverter works for all of these, with the exception of the DA APS-C format $500 1.4X converter. All other 1.4 or 1.5 converters do not have the in lens motor to camera body contacts. When going 2X (I have the Pentax A-S 2X, and the Tokina A-S 7 element 2x, and an old K mount Vivitar matched multiplier of ill report on the forum [which works great with a straight 200mm to make a sharp handholdable compact 400mm f6.3], all are MF) you may discover that there is one Promura/and other labels 2X AF (all of the same manufacturer) with the mentioned motor contacts -- but it was actually made for the early FA power zoom connection, and simply does not settle to autofocus with in lens motor zoom lenses, or slot-screw AF lenses. It will search and search and never arrive at autofocus. So, excepting the Tamron, and the Pentax DA 1.4X you are looking for a converter which most likely will be manual focus in application, unless just needing the screw-slot type of autofocus linkage. At the very least find one with the A/F(A, DA, DFA) series lens information contacts, not just a straight, now at least 35 year old or so K mount. Then the in camera aperture control will function.
In addition to looking on Ebay, Amazon, KLH, etc, look at used Pentax on Adorama and B & H, and then search for Pentax used lens outlets, some of which are specialty stores on Ebay, and may not show up on a general Ebay search. There are several advertising vintage PK and its offspring lenses and accessories. I am sure a Tamron F 1.4X is out there, finding a good price is uncertain.
The ones mentioned will give good focal length upgrade results, with the 2X costing two f stops off the original lens widest aperture, which can be difficult to preview through, the 1.4X costing one stop, and very very few of available used converters otherwise out there not creating more problems to focal length conversion than they supposedly solve. Go with a 1.4X which works to your best advantage with the gear you have, or think you will have. The 2xs are a mixed lot, mine work OK, but handling a 2X without a reasonable tripod or window mount and bright light is very shaky with long teles (in converting optics of 250mm and above, including camera crop factor). The 1.4Xs used, I know by use work very well, have few abberations, and are easily hand holdable, or mountable to readily grant their focal length upgrades. Recall too that shutter speed needs to go up with increased focal length, or blur due to camera shake will occur. As with a sensor crop factor, depth of field will lessen as focal length increases. Aperture selecton will be affected, as stated. F2, will become f2.8, 4 will become 5.6, if selected on the on lens aperture ring, otherwise put it on the A setting and let the camera figure. An advantage is that they can get you closer to a subject than an alike actual focal length achieved original lens.
I recently reviewed the Sigma 150-500mm full featured 21st century zoom, find it under third party lenses on the Forum: Sigma recently discontinued legacy lenses, out of production lenses, where I comment on using the 1.4X with that fine and fieldable optic. No third party manufacturer is currently making Pentax AF teleconverters, so, you are diving in a still water pond attempting seeing to the bottom through a mirky history of present availabilty to find what you need among those selling used or almost new gear settled into that now aging source.