Any advice on choosing a AF teleconverter?

Hello fellow Pentax Users. I' ve been recently thinking about buying a 1.7x teleconverter, but really have no idea which one to choose, for best IQ and AF ability. Does any of teleconverters support SDM (or HSM from sigma)?

I would really appreicate any advice, as I really have no experience regarding TCs.

Cheers, Luka

If you have about £200/£235 to spare, the SMC Pentax-F 1.7X AF T/C is excellent as it provides AF to MF lenses. IQ is fine too.

As for SDM/HSM, I can't help.

i have been on the look out for an sdm too for use with my 200/2.8. preferably a 2x.

i gather a Kenko 1.5x Pz-AF Teleplus DG hits the spot for sdm lenses, but i'd rather a 2x. i've heard a tamron 1.4x (dont know which one) also works.

don't hold me to the above—i'm new to the k-mount, and read the above things elsewhere, but haven't tried either tc for myself.

I have the Tamron x1.4 Pz-AF MC4 Teleconverter which works with the Sigma HSM system. These go for approx £140 on the forum.

The shot below was taken using the Pentax SMC-DA 55-300mm with the TC on a K10d camera.

[IMG]http://i941.photobucket.com/albums/ad254/weldingblues/Bedford/Swanseranade-resized.jpg[/IMG]

I was told that the 2x is not as good as the 1.4 (both Sigmas)
Hope this is of help.

The DG version does not work with SDM, you need one marked SHQ and I believe they are not made now.

Thank you all for your comments. It's good to know what to even look for
@ gillbod: Did you notice any degrade in IQ with Kenko TC?

Cheers, Luka

Luka,

I got a Tamron 1.4 TC recently. I've used it with my DFA100, but tried it out with the DA17-70 to see if it worked with SDM. It did.

As long as you stop down slightly (past f4), the image quality remains excellent (with the DFA100). (If I'm not mistaken - a problem with TC's is that the EXIF only shows the lens' focal length - my entry to last week's DoF comp was taken with this combination - link).

I also got it in the hope that the focusing would work with the Sigma HSM (I am picking up a 50-150 at Xmas). However, I'm not sure it does - I recall reading something that cast doubt on this (that it worked with SDM but not HSM). Welding Blues - have you actually used yours with a Sigma HSM lens?

The Tamron comes up periodically on Pentaxorums - I got mine for $180 inc.

Hi Dr. Mhuni,
Yes I have used it on a Sigma 120-400 HSM lens, its a s you say the EXIF data does not show the total length.

I only have two test shots at the moment, if required can show them here later today.

BR

Great, thanks for that Colin. No need to upload images for me - I was just curious about whether or not the AF would work with HSM.

I would certainly recommend this TC in that case, Luka. From what I understand, the Tamron is at least the equal of the Pentax 1.7. It's also considerably cheaper (half the price of the Pentax) - though it is shorter of course. Still it would convert your Sigma 50-150 to 70-210, which is handy.

Judging by users' feedback, these two TCs stand out from all others IQ wise.

For digital use the Pentax Rear Converter-A 1.4X - S is very similar
to the 1.7x. Works well with the 55-300mm MF only. Loses slightly
less light than the 1.7x

the rule of thumb is the higher the magnification, the greater the loss of IQ (and light, obviously...but this can be offset by going to higher ISO with newer bodies). So its a trade-off, unsurprisingly.

However, I've never quite understood the point of a 1.4x TC, it seems such a marginal increase in zoom... (and little different than getting a higher-resolution sensor, or just doing a bit more cropping, which for anything less than billboard-sized printing shots isn't really an issue nowadays...)

Having had both at the same time (and selling the Tamron) I have to say that the Pentax teleconverter is superior when it comes to IQ, even though it is 1.7x. It may not be fully AF as such but it does allow you to input the focal length so you know SR is working properly. I did tests with a 200mm f2.8 and 300mm 2.8 and the Tamron can also cause purple fringing in some cases.

Of course the Tamron is half the price and works with SDM (whereas the Pentax converts the lens to screw drive) but if IQ is the main aim then the Pentax 1.7x is better (imo).

Has someone already mentioned the Pentax 1.7 also gives you AF when using a MF lens??

Good to know, Mike.

Flossie - prior to getting the Tamron I wondered about a 1.4 TC. But it actually does make quite a difference, and is preferable to cropping as you can pay more attention to the composition at the time of taking the shot.

the Pentax 1.7x does this by having a small amount of focus in the actual Teleconvertor. So you manually focus to "almost there" and the TC does the fine-tuneing.

That's why the 1.7x commands such a huge price premium second-hand (you can't get it new any more *slaps forehead*).

There are rumours of Pentax talking to people about new SDM TC's, but could come to nothing, don't expect anything anytime soon...