Teleconverters

I'm thinking about adding a Kenko 1.4x dg pro teleconverter to my bag, mainly to use with the SP90 but also to use with the 400mm f5.6 on bright days.
ANyone tried them? is it worth giving a go?

I tried one, not that model mind, and found it virtually useless. It converted a good 50-200mm Pentax lens into a dog. Not one usable handheld photo with the teleconverter in use. Maybe I wasn't using it properly but it was a disappointment. Just my two cents worth.

My 2p regarding teleconverters:

With one or two exceptions (the Pentax SMC-F 70-210 being one), consumer F4.5-5.6 zooms should not be used with them.

This is because the combination is too slow to be reasonably used hand held even wide open, and most authorities agree that a teleconverted lens should be stopped down at least a stop or two in order to get decent quality. You end up with a working aperture of at least F16 and camera shake ensues.


With decent fast primes (and presumably F2.8 zooms, I've never owned one) a teleconverter becomes very useful indeed. My Tamron 90SP makes a lovely 180mm F5 when combined with my Tamron 2x SP Flat Field converter.

As a general rule, if you can keep wide open aperture wider than F5.6 then things will probably be ok. Combinations having a max aperture narrower than F5.6 are at best hard to use.

I use both the Pentax 1.7Af convertor and the A 2X-S convertor although this is mainly on the 2.8 primes but also on the 300/4 A*. Both of these give good results with the fast primes. However in the past I have tried various others including the Tamron SP. Of thes only the Tamron was really usable and even then was not up to the standard of the Pentax ones.

Kim

Could you use a TC on a DA* lens? Would you loose the sdm function completely?

Anyone tried to use a TC on the new lenses????

no TC I am aware of passes through the power contacts for the SDM/PZ motors, so yes you'd loose SDM completely. Should still be able to focus using the screw drive (given an AF teleconverter of course), though obviously it wont be as fast or as quiet.

Other than that the DA*'s should be ideal for TCs, very high quality, very fast lenses.

I regularily use a 2x TC (a 7-element one) with my 80-200 F2.8 and it works very well apart from introducing a bit of CA. A 2x TC on a cheap consumer spec lens like the 50-200, or even a better lens such as the Sigma 70-300, isn't a good idea however and the results won't be great.

A decent 1.4x you might get away with in those same circumstances however with the 90mm and 400mm primes mentioned and in decent lighting conditions I'd certainly expect the results to be useable.

I've just had a look on the Intro2020 web site and as I suspected I don't think Kenko do the 1.4X Pro converter in pentax fit.
I have the Kenko Teleplus DG 1.5X converter and have had some good results when used with the Sigma 100-300mm EX F4 lens, it is better to stop the lens down so you need bright light to get a fast enough shutter speed for wildlife shots, but AF is still possible and fast enough to be usable.
I also have the Pentax 1.7X converter and the same rules apply, it is only practicle to use in bright light, I think it is better to use converters with a F2.8 lens but we can't all afford one of them.

The Teleplus and Kenko TCs marked PzAF pass through the power contacts for the power zoom motors. I presume this means they will pass through the SDM function correctly, but haven't (yet) got hold of an SDM lens to try it with.

really? awesome! if they pass through all 7 data contacts plus the two power contacts, then SDM should work.

I have just got a Kenko TCs (mc7) marked PzAF, it does not work with DA* lens. No screw autofocus and no sdm, the DA* just becomes a manual focus len. Luckily, I am not buying that TCs for serving my DA*. But for those thinking to buy a PzAf TCs for matching the DA* and sdm will be workable, please be awared.

Not wishing to contradict you, but I've done a fair few tests with the Tamron SP 2x with all sorts of lenses including the Tamron SP90 f2.5 and my Teleplus macro focusing 2x TC made by Tokina is better. Of course as is always the case with TC's some lenses perform better or worse with different lenses. So if the tamron impresses try the Teleplus or its previous manual only stablemate - the Vivitar 2x macro focusing TC.

I have been using a Tamron 2x Pz-AF with a variety of Sigma and Pentax lenses with decent results all the way to 1200 equivalent mm. While not as sharp as a dedicated lens in that range, the cost is certainly lower. I took my camera and lenses to a local pro shop and tested this out before purchasing the Tamron.

I've just ordered a Tamron 1.4x converter with, what I am lead to believe from another forum, a pass through for the SDM connections which works fine. Will find out when it arrives, and let you know.

Also, noticed in the (German) K20D manual that Pentax are listing 5 different tele-converters in there, who knows what is in the pipeline!?

let me know how it works out for you as I always have new students asking .

al