Decent 1.4x and 2x AF teleconvertors?

Any suggestions about decent teleconvertors in Pentax AF fit (including UK online suppliers if possible)? Primarily for use with a Tokina ATX-Pro 80-200 F2.8.

I've got a cheap 2x one I picked up years back but it's not very good.

I have the Pentax AF 1.7x adapter and have got some great results using it.

It's also an interesting thing because it focusses internally, allowing you to use a manual focus lens in AF mode! And it's also useful for large lenses, since the lens itself doesn't focus, but only the AF adapter. Makes it nice and quick!

Matt

I had one of the Pentax AF 1.7x adaptors but sold it as I'd switched mostly to AF lenses. I did try it with the 80-200 F2.8 and it did work however the focussing performance was slow.

Fair comment. I haven't found a problem with AF speed, personally, but I don't have an f2.8 telephoto
Coupled with the SMC-F 70-210 and SMC-FA 80-320 it performs very well.
Matt

To partially answer my own question - I've not got one of the 7 element 2x Teleplus convertors and it seems considerably better than the 4 element one I was using before.

The only slight inconvenience that I've found with the 1.7x AF adapter is that you generally set the main lens to infinity and allow the adapter to do the rest. Sometimes the subject falls outside the range of the adapter and it simpy can't achieve correct focus, the solution is to approximately focus the lens first (or adjust it when the adapter fails).
This only really applies to lenses with shallow depths of field ie. telephotos and tele-zooms toward the long end, standard and wide-angles are normally ok - depending of course on subject distance!

No matter how much you tell yourself that you should only use adapters with prime lenses, you just can't help trying outrageous combinations such as: AF 1.7x + MF 2x + 75-250mm zoom

teleconverters introduce their own abberations to an optical system, but also magnify the lens's existing ones. The 7 element ones are not bad, but for the highest quality I don't think any of them really meet the challenge.

I'd prefer a second hand longer lens any day, keeping the cost down by not buying new.

Agreed John, but when you bear in mind that you can dramatically increase the focal length of your lens with the simple addition of an adapter/converter that is small enough to fit in your pocket, there are times when it's the most convenient solution - esp. if it means the difference between getting the shot or not!

I once owned a cheap Vivitar four-element 2x converter and it really wasn't at all bad, I think the AF 1.7x is six-element and undoubtedly better and the eight-element Tamron SP flat-field converter is superb.
Generally speaking, a good quality converter is a very handy bit of kit and you'd only get poor results with a low quality object lens.
A reasonably fast, good quality tele lens is definately a better option, optically speaking but size and weight (not to mention cost) can be an issue.

This morning I've been playing around with 2x + 2x + 500mm! None of my tripod heads are really up to holding it steady enough though...

Niblue

I have an Sigma APO 2x EX converter which is probably one of the best you can get.
I will post some shots tomorrow takenwith my Sigma 70-200 f2.8 with and without the converter so you can judge for yourself, I would do it tonight but I'm just home from Edinburgh and the light is fading, hopfully we will get some more sun tomorrow.

I hope it is sunny tomorrow as I was planning a walk in the Pentlands with my son and my 10-20mm in tow!

Niblue

Been a bit dull over here today, still I managed to do some comparisons with a colourfull mug .

You can view some 100% crops at www.pbase.com/mcbrian/miscellaneous/, you can find them in the miscellaneous gallery.

The RAW files were processed with Capture One with no manipulating, sharpening and threshold were both turned down to zero and converted to 8bit Tiff files. No PS manipulating only the use of Matt's action for the sharpened images.

Hope this helps, if you want the DNG files drop me a PM, the zip file is 102MB (more images than I've shown).

Brian,

Those results look pretty good and certainly I'd expect a 70-200 F2.8 with a good 1.4x or 2x to outperform a consumer zoom which goes to 300 or 400mm. I've seen the 1.4x Sigma on sale in the States but it only seems to list as being compatible with certain lenses, probably because there is a forward projection of the tc's elements. My Tokina 80-200 F2.8 isn't listed as compatible although I think it should probably work.

My son and I did go for a walk in the Pentlands despite the weather - it was mostly dry but overcast and quite windy so we only went up one of the smaller hills (Hare Hill). Because of the overcast I was shooting with a ND grad most of the time and the results weren't much to right home about in composition terms, however I'm very impressed with the Sigma 10-20's optical performance although even with my cut-down Cokin P holder you have to take care to avoid vignetting at the wide end.

I also took the Tokina mirror lens and got a few useful shots of a swan on one of the lochs. I blew what would have been the best shot though as I didn't have the focus spot on. The composition was pretty good as the swan had just dipped its head under the water and I caught it as it came back up with water dripping from the beak, water droplets on the feathers and the curve of the neck and head filling the frame. Some manual focus practice with the lens is clearly required...

Regards
Steve

Not the best day for a walk was it, I had planned to walk the beach from Leven to Largo but was directed to do the washing instead wile my wife was out on a cat rescue.... open washing machine door, fill drum with washing , fling liquid ball in, shut door, press go, open fridge door, remove bottle of coo.............l bud, shut fridge door, walk to living room, arrange cusions, lift feet to horizontal position, press 401 on remote, watch footie, drink bud, repeat 2....3...4.....5.... times from open fridge door, fall asleep......wife come in from a cat rescue and resumes operations from washing machine.........

My FAJ 18-35, FA24-90 or FA80-320 all fit on the converter but you have to be very carefull and not use them at the short end, so really I don't bother to couple them at all. The FA100 f2.8 macro does not fit, the Tokina 500mm will fit but you have to take the rear filter out to do so, the SMC A 24 f2.8, SMC A 50 f1.4 and F50 f1.7 all fit and operate crrectly.

All this talk of the 1.7x AF convertors making me jealous - I keep an eye out, but not seen one yet - anyone got a spare?

Dan