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06-04-2013, 10:03 AM   #1
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AF Teleconverter that will work with DA 55-300

I'm looking for an autofocus teleconverter (screw drive pass-through) that will autofocus with my 55-300 kit lens and also be reasonably sharp. Tamron? Kenko? What are my options?

K-x and K-01... but I'll likely mostly use it on the K-01.


06-04-2013, 10:16 AM   #2
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Pentax used to make an AF 1.7x teleconverter.
06-04-2013, 10:30 AM   #3
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This one works reasonably well.

Vivitar 1.4x Tele Converter for Pentax VIV-1.4X-P

It was used with the 55-300 in all the outdoor shots in this set...

Montezuma NWR & Audubon May 04, 2013 - a set on Flickr

Not sure how it would work with CDAF...with PDAF I sometimes have to AF at 55mm then zoom to 300 and fine tune.
06-04-2013, 10:38 AM   #4
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I just sold a 2x Kenko that worked ok, only real loss was contrast. The Vivitar 1.4x comes in several flavors and the one I have works well with the 55-300 and it can be had new for <$100 from Adorama and B&H.

06-04-2013, 11:23 AM   #5
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QuoteOriginally posted by ChopperCharles Quote
I'm looking for an autofocus teleconverter (screw drive pass-through) that will autofocus with my 55-300 kit lens and also be reasonably sharp. Tamron? Kenko? What are my options?

K-x and K-01... but I'll likely mostly use it on the K-01.

You'll run into issues as the TC would make the lens turn into a F6.7-F8 lens or worse, and at those apertures, the AF will not work reliably.

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06-04-2013, 11:40 AM   #6

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The 55-300 is quite a good kit lens, but as Adam suggested, putting a TC on it is really pushing it. I think I tried it briefly and quickly gave up.

Better to crop your shots or get a better lens at this point. I finally realized the 55-300 is somewhat weak over ~135mm. So I sold it and got a DA*50-135. Later added a K200/2.5 and F*300/4.5. Much more money, I realize, but it's likely this is what you're really looking for, rather than longer focal length.
06-04-2013, 01:49 PM   #7
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The Kenko 1.5 Pz-AF worked very well with all my screw mount lenses including a similary AF zoom the Tamron 70-300.
I suspect it would work just fine with the 55-300 as well.
Resulting IQ may not be what you expect, although the Kenko is a decent quality converter.

The same Kenko did not work well on my SDM or HSM lenses, even though the contacts were present.
06-04-2013, 01:55 PM   #8

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My GF uses the exact same set up, K-01 and 55-300 for wildlife.

Here's what I have found as I tried to equip her with a good kit but stay reasonable in money outlay.

The pentax 1.7 was out, people asking for 350-400 for it took it out of the picture quickly.
Sigma's TCs won't mount period, I have both the 1.4 and 2 for my wildlife lens and the rear element doesn't match and allow a connection
Tamron 1.4 gets mostly positive but some mixed reviews, but sells at a premium if you can find it (around 300) again too pricey
The vivitar seems to have the best subjective image quality, but doesn't like to autofocus with slower lenses
kenko makes (made?) a 1.5 that is reasonable, but nearly as tough to find as the tamron

I ended up getting her a promaster spectrum pz-af or soemthing like that. it's a 1.7x but despite all claims to the contrary, she has had NO problem getting auto focus lock on her K-01. the only issues she has is if trying to lock onto a camoflauged animal in total shade. (I guess not enough contrast?) she's used it on deer and squirrels and elk so far. I haven't done side by side comparisons to 300 cropped versus 300+1.7 uncropped, but the images she took with the 1.7x seemed pretty decent when she could keep things steady.

I've even tried it on my K5iis and it works reasonably well and autofocused the 55-300. the nice thing about this TC is you can grab one for about $85-100. at that price it's worth having around for occasional use

06-04-2013, 03:19 PM   #9
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I second the Promaster Spectrum 7 Z AF - 1.7x , when i had a DA 55-300 i used the TC with that lens on a K7, autofocus was a bit slow but accurate. I would suspect that the Tamron 1.4 and the Kenko 1.5 will work in the same manner (i have both and have not had any problems on the k7 or k5 using screw-drive lenses).
06-05-2013, 06:42 AM   #10
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Coolness. Promaster sounds like the ticket, if the image quality is reasonable. I'll look into it more.


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