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08-20-2007, 06:57 PM   #1
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Tamron 1.4x Teleconverter & Pentax FA 50 1.4

Hi Guys,

I have been reading mixed reviews of Teleconverter lenses and am now a little confused on the issue. I am about to purchase a Pentax FA50 1.4 and had intended to buy the Tamron 1.4 TC for the hell of it. I shoot weddings and thought that by using the FA50 with the TC i would get roughly 70mm (if you want to consider crop factor it will be more but i just take the actual lens measurement) at about f2-2.8 which isn't too bad, especially in lower light areas such as the church.

On another thread someone had mentioned that a TC won't work on anything less than a 100mm? By looking at the Tamron 1.4 TC it doesnt appear to have any element sticking from the lens, elminating possible damage.

By reading some reviews on the TC someone had adv that it will work autofocus with a zoom lens, but that isn't my primary reason for wanting to purchase. A little extra on the FA50 1.4 is.

Will the 1.4 Tamron TC work on the Pentax FA50, if so will I lose autofocus?

I have the Tamron 18-250 and love it. I'll be in Africa in early Jan on safari and figured that the TC may help give the Tamron a little extra reach at the long end. At around f11-f13 or so if it is a good day with the K10 set to an ISO of say 400 you would expect to get a decent shot of sorts wouldn't you?

Will the 1.4 Tamron TC work on the 18-250, if so willi lose autofocus?

Does anyone have any experience, knowledge and advice. Many times peoples feedback on this forums have guided me into making the right choice camera/photography wise. Feedback is appreciated.

If i could buy a 300mm f4 or 2.8 that would be great, but like most people i'm not made of money and I buy my lenses for what i'll need them for the most. After all they aren't cheap!


08-20-2007, 07:35 PM   #2
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If you get an autofocus TC (like the Tamron 1.4x), you will not lose autofocus as long as the effective wide-open aperture of the lens with the TC is large enough.

With any AF lens f/2.8 or faster (and probably f/4 or faster with a 1.4x), you should not have any AF problems. You may notice vignetting or other weird effects when using a TC with a 50mm lens - It's kind of borderline in that case, that's why manufacturers have reccommendations of only using a TC with longer lenses.

With the Tamron 18-250, you may or may not lose AF. Officially, if you go above f/5.6 wide open you lose AF functionality, but manufacturers have discovered that this can be pushed. For example, a few lenses (such as the Tamron 18-250 and the Bigma) have wide-open apertures of f/6.3 at the long end and still AF fine. Many have used f/5.6 lenses with 1.4x TCs and retained AF, although with noticeably degraded performance. (Lots of hunting/slow AF even in broad daylight.) The Tamron 18-250 will be really pushing it as far as AF goes at the long end.
08-20-2007, 08:52 PM   #3
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Join Date: Sep 2006
Posts: 220
QuoteOriginally posted by switch79 Quote

On another thread someone had mentioned that a TC won't work on anything less than a 100mm?
I read 50mm minimum somewhere. It might have been in the owner's manual, which I can't find right now.

QuoteOriginally posted by switch79 Quote
Will the 1.4 Tamron TC work on the Pentax FA50, if so will I lose autofocus?
Yes it will work, and no, you won't lose autofocus. It will not focus as quickly because there is a reduction gear in the AF drive of the teleconverter. Other than that, nothing particularly weird happened when I used them together.

I wouldn't expect to get very good results with the 18-250 zoom lens, though.
08-20-2007, 09:36 PM   #4
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QuoteOriginally posted by switch79 Quote

Will the 1.4 Tamron TC work on the Pentax FA50, if so will I lose autofocus?

Will the 1.4 Tamron TC work on the 18-250, if so willi lose autofocus?
I owned a Tamron 1.4X tele-converter for a while. It was the current model with the AF coupler.

I tried it with a Pentax F 50mm f1.7. The combination does function, and will auto-focus. AF speed is reduced due to the extra drag. Image quality was pretty poor with the lens wide up to about f/5.6. From f/8 on it was better. I would expect similar results from the FA 50mm.

There are a lot of lenses in the 70-100mm class available used for a modest price. They are likely to give better results than the 50mm with a tele-converter.

I've never had a super-zoom like the Tamron 18-250mm. Due to the slow speed at the long end (something like f/6.3) it will be something like f/9.5 with the 1.4X converter. This combination will not auto-focus reliably. And super-zooms are not the best performers on the long end. It will operate with manual focus, but I would expect the results to be unsatisfactory. Again, you are better off with a used lens. Something like the manual focus SMC 300 f/4 (plain K mount) is available pretty cheap, and that would give you some extra reach. And that lens would work pretty well with a good 1.4X converter.


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