[Sten]

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I am considering buying a teleconverter for my K-5 and its lenses Pentax 18-135 and Sigma 70 2.8 macro, possibly also for my Sigma 10-20 3.5. I am not sure about 1.4 or 2.0 or both.
Which teleconverter should I choose and where can I get it? I live in Stockholm, Sweden. I have visited Sigma's website, but their web application could not provide a dealer for their teleconverters.

[luftfluss]

Hi Sten, I believe there is no teleconverter that is compatible with the 18-135 because that lens uses the DC motor for AF. I would suppose that you could focus the lens manually with a teleconverter.

I'm sure that if I am wrong, someone will come along and correct me!

[Adam]

I wouldn't put a TC on the 18-135mm, as it would probably completely butcher the IQ. And no, there aren't any SDM teleconverters out there yet, but Pentax will be coming out with one next year!

It seems that conventional AF teleconverters are available, though, such as this vivitar:
Vivitar 1.4x Teleconverter for Pentax VIV14XP B&H Photo Video

[RKKS08]

I can't comment on the possible AF issue luftfluss mentions. But in any case be careful before buying the Sigma 1.4x DG EX APO Teleconverter. Its front lens is protruding, and with some lenses both the lens and the TK can be damaged. Sigma used to have a compatibility chart on their website. Not even all Sigma lenses can be used. But it is extremely small.

[Sten]

Thank you, luftfluss, Adam, and RKKS08!
There are obviously considerations in connection with this.
Perhaps I should refrain from buying right now and wait for possible future Pentax TCs.

[cmohr]

I don't believe the Sigma TCs will work with any of those lenses, as RKKS08 mentions, the rear element of all the lenses you have are flush with the mounting of the lens, the Sigma TC's protrude into the compatable lenses by up to 18mm (with the 2x) so they will not even physically join to your lenses. You could try the Kenko Pz-AF 1.5x TC, as it does actually work AF on SDM lenses, but as Adam said, IQ will suffer. What focal length are you trying to achieve??? For the price of the two Sigma TC's you could maybe just buy another longer lens.

cmohr

[baro-nite]

I have no experience with the Sigma TCs, but they are generally considered best to use only with specific Sigma lenses. Sigma's own list of matching lenses does not include the 70/2.8 macro or the 10-20. (Putting an ultra-wide on a TC seems like a rather unusual thing to do anyway.)

I can confirm that the currently available Vivitar 1.4x TC does work with the Sigma 70/2.8 macro, but I prefer to increase magnification on this lens by using extension tubes and/or cropping instead, to preserve its desirable optical characteristics.

[cmohr]

You know, its not AF but something like this could be what you are looking for. A Macro teleconvertor with variable macro and it has the A contacts for correct aperature control.

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[vonBaloney]

I have a 2x TC that allows standard auto-focus -- it has pass-through contacts for aperture control and passing of data, as well the drive mechanism to focus (it passes that through as well). AF doesn't always work so well because you lose too much light with the thing, but on a fast lens it is ok. It is a Vivitar 2XMC7 AF from a few years back -- seems like it was available only a very short time. I think it is the same as the equivalent 7-element Kenko. The contacts actually annoy me because they report the original focal length back to the camera rather than the doubled one, which means the SR won't be using the right parameters which means I turn it off which bugs me because when I double the focal length and lose stops from TC, I need the SR more than ever (or a tripod). I figured out which pins to block out, but it is a pain...

[stanislav]

As mentioned earlier the question is what do you want to achieve with a TC.

They are usefull for fast tele-photo lenses, and you do not seem to have any of those. I have used TCs on my Sigma 70-300 just to get longer focal range, but I do not see a point in getting a TC on anything shorter. So if your objective is to get a longer reach on a budget get something in range 70-300 (Sigma or Tamron) or perhaps Pentax DA 55-300 or some older FA glas.

There is also a macro focusing teleconvreter which is a teleconverter on a helicoid tube (like one chmor mentioned). If yuo find a good one at affordable price you can get yourself a fairly cheap macro setup (at least compared to real macro glas). However if you want that to work, you would tipically need a fairly fast prime glas (like 50mm f1.4, 50mm f1.7 or perhaps 35mm f2.4). The converter mentioned above is the one ghat would give you 1:1 magnification with a 50mm lens that focuses down to 0.45m. With wider glas you can get past 1:1 and actually get higher magnification. In that case the limiting factor is that you'll bump into the object with the front element of the lens.

I live in Stockholm too and happen to have 4TCs (all with A contacts - Kenko Pz AF 1.5 and 2, a macro focusing teleconverter 2x and one manual 2x). So if you would like to take a look at them and see how they fit with your lenses, drop me a private message so we can perhaps arrange a meeting somewhere. With a first-hand experience you'll be able to make a better decision on what would actually work for you.

regards, Stanislav

[selar]

While its true that there arent any "officially" SDM compatible telecpnverters, there are atleast three that i know of and one that i own and use that work with sdm and hsm. They are the ones that have the pz-af contacts for the fa series power zoom lenses. There is a Kenko Teleplus SHQ 1.5x which is the one i use, a tamron and the third is a sigma. No pentax teleconverter works with sdm or hsm, however there is a 1.7x af converter which is primarily meant to convert manual focus lenses to af that can be used to provide an af solution for sdm and hsm lenses.

[Sten]

I feel a little confused but also impressed by the knowledge and willingness to help in this forum.
Thank you all!
It is now clear to me that there is no simple and obvious solution.
My intention was to have a possibility to extend the range that took only a little space in the camera bag.
But perhaps I was too optimistic.

Best regards,
Sten