Which MF Pentax Teleconverter Recommended?

I have a very good experience with Tamron SP 2x Teleconverter, but I mainly used it with K135/2.5. The images were reasonably sharp. However if you attach M*300/4 to it focusing will become a quite a trouble.

Take a look at this folder on Pentaxforums:
http://www.pentaxforums.com/userreviews/reviews-Pentax-off-brand-teleconverters....

Quite a few TCs have been reviewed - although some of them are sold under different brand names in the USA to those in Europe. Also, there is a more restricted range of Pentax-fit TCs than is available for CANIKON fits (e.g., AFAIK, no Kenko MC-7 7-element version)

I would seriously not go for a 2xTC as that would give you a 600mm F8 combination which would be difficult to focus manually due to the relatively dim image in the viewfinder in anything but very good lighting conditions.

The Kenko MC4, also (I think) AKA the Kenko Pz-AF 1.5x Teleplus SHQ (which I have, but have not used a lot as I now have a Sigma 1.4x which definitely one of the best 1.4/1.5x available in Pentax fit and I love it ), seems to be a fairly popular choice at the lower price end - but some should be avoided like the plague!

Wonder if the Sigma 1.4x would fit the Pentax lens - it works well on the Sigma 70-200mm F2.8 I have. Problem is that the front element of the Sigma projects well ahead of the front mounting face for the lens. Therefore it will not fit to any lens where the rear element is not well recessed into the mount on that lens. It's also pretty pricy - I got mine a couple of years ago for £125, but the current retail price is around £200

Is there any up to date thinking on teleconverters? I have had my 60-250 for a while now and it gives excellent IQ. To have 500mm would be really useful for 'nature'. If I could achieve this with a 2X converter, without sacrificing too muchon quality, it would make my life complete (at least, for a while).

A word of caution: I have the both the Sigma 1.4x and the Sigma 2x (cost me a £100 new about 3 yrs ago!). I have tried them both with both the 70-200mm F2.8 and 100-300 F4 Sigmas (both non-OS), and I rarely use the 2x as it slows down the focusing no end, and the lock-on is much more iffy - sometimes it is OK, and other times not, especially if the light is not that good. Even then, the 1.4x always locks on quicker with either lens, and the more so with the 70-200 F2.8.

So, if you are shooting objects/animals that are fairly stationary at a fairly constant distance then you may get away with the 2x on an F4 lens - otherwise, if you shooting at something which is moving quickly and approaching/receding, then I would not recommend the 2x converters. That is particulary true with Pentax DSLRs where the autofocus - even on the K5 - is not as good as some competitors.

that gives me something else to think about - thanks. The focussing thing could be a real factor when dealing with flighty birds.
Is the IQ of the sigmas good? i.e. better than just blowing up the picture without the TC?

The IQ of the Sigmas - especially the 1.4x - is good, but they only work with lenses with a recessed rear element, and they won't work with Sigma's HSM lenses.

I realise that - although maybe I did not clarify the points to sophiecentaur! - but what I was trying to point out was that a 1.4x T/C is a far more realistic prospect than a 2x.

Therefore a Kenko (etc.) 1.4 should be a viable solution, whereas a 2X might well not be - albeit, as you say that it would have to be used in manual focus mode. Again, a 2x would be less desirable as the viewfinder image would be dimmer, and so it would be more difficult to focus manually.

BTW - I think that HSM-compatible versions of both the 1.4x and 2x T/Cs are/soon will available (in Pentax mount??) for the Sigma HSM lenses.

Hate to take issue with you Tim, but I have the 1.4X and it works (fine AF) with my 100-300mm f4 EX DG, which is an HSM lens.

FYI, however, when lens and TC are used with my K20D there is an aperture (?) communication problem, necessitating EV compensation to be dialled in on the camera. Annoyingly, the amount needed varies according to the aperture set, resulting in my using the TC with the 100-300mm much less than anticipated.

Jon

I thought Sigma 100-300mm F4 didn't come with HSM.

And I thought the Sigma TCs didn't have the HSM power contacts? Is your 100-300 using the screw drive?

You're right, and so was Tim - my apologies to you both, and any others, for disseminating this misinformation The lens is HSM in all but the Pentax mount. In practise, however, the speed and accuracy with which it focuses, even with the 1.4TC, would lead you to think it was; the only giveaway being the noise, which can be a problem when stalking wary wildlife. Under such circumstances, I often switch to MF, which is reassuringly swift and positive with this lens.

Suitably chastened,

Jon

Well done Steve for spotting this..... saved someone from making a very expensive mistake

Sigma really should get their act together and standardise across all their lenses. If you look at the compatibility chart for their TCs you need to be a rocket scientist just to figure out the various incompatibilities and differences depending on mount. For instance why does the TC transmit correct exposure information for some lenses, but not others, and why only on some mounts, but not Pentax? Grrr.

Even the chart has mistakes. What is that *5 note all about? 100-500 zoom on a 180mm macro lens? Duh.

A slight aside: I had the 100-300 F4 in use at Wings & Wheels at Dunsfold yesterday, and I found out one disturbing thing about combining it with the Sigma 2x TC on the K5:
It was almost impossible to manually adjust the focus with the TC attached, and very concerning because you could clearly hear a clutch slipping loudly inside the lens when you did try to do that - I stopped as soon as I realised that because, whatever it was, it did NOT "sound good".

Won't try that again, and if I do use the two together, it will be for pics that don't require a lot of rapid focus distance adjustment, and so the lens can be left to autofocus in its own time!

OTOH, I don't get the same problem, or at least to anywhere near the same extent, with the 2x on my oldish 70-200 F2.8 - which does work reasonably well, but, as I said before, not autofocus very quickly.

No one mentioned the Pentax SMC F 1.7x AF Adapter. Makes the MF lens a very fast auto focus lens!