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11-21-2012, 02:57 PM   #1
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Considering different Kenko teleconverters, need input on which to choose

Hi, I been considering a teleconverter before, but it has now been more of a reality since I finally bought the tamron 70-200 2.8. I have been considering several converters, both old used ones and brand new, but find it difficult to get good and decent reviews on them. I am currently considering some kenko converters, and the main choice is to choose between a 1.5x AF DG Teleplus converter or the 2x AF DG converter (either the MC4 or the MC7 that seems more than twice the price of the MC4).

Anyone with first hand experience on either of those? what do I loose with the 2x converters that I don't with the 1.5x converter, besides the obvious loss of 1 extra f/stop.

Would be grateful for any inputs on this.

I would primarily use this to hunt for birds and simple wildlife. I am aware that a TC will not be a fullworthy replacement of a true 300/400mm lens, but for my vallet after buying the 70-200 it is a obvious choice.

11-21-2012, 03:23 PM   #2
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I've had the Kenko 1.5x teleconverter for several years and all I can say is that it works as advertised. It understands SDM lenses, although below f4 it's focus can get unreliable with an SDM lens (and I can verify that this is true, but not a big issue). When I was researching buying one, everything I read was that the Tamron was the best of the bunch. Don't know whether that's true or not. The Kenko has been just fine in my book and I use it on a number of lenses including the Tamron 70-200 f2.8 lens.
11-21-2012, 03:27 PM   #3
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I use the Kenko and the Tamron: both are very capable. I'm wary of 2x TCs though.
11-21-2012, 03:39 PM   #4
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At one point I have a copy of Tamron 2X TC and a copy of Tamron 1.4X TC (both now sold). The Tamron 1.4X TC is very similar to the Kenko 1.5X TC.

Both of the 1.4X and 2X TCs have power contacts, but while the 1.4X TC can somewhat autofocus with DA* zoom lenses, the 2X TC just doesn't autofocus at all.

I write "somewhat" because it tends to hunt a lot, particularly at the long end of the focal length (there is no reason to use the TC with a zoom lens at the short end of the focal length).

There's a reason why the 1.4X TC is twice the price of the 2X TC.

Neither of them is as good as the Pentax 1.7X AFA, both in terms of IQ and in terms of autofocus capability.

11-21-2012, 03:44 PM   #5
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I will say that in the manual, the Kenko TC clearly says that below f4 it will be unstable for AF with SDM lenses.
11-21-2012, 04:01 PM   #6
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QuoteOriginally posted by blackcloudbrew Quote
I will say that in the manual, the Kenko TC clearly says that below f4 it will be unstable for AF with SDM lenses.
The problem of focus hunting is exactly the same with all DA* zoom lenses, including the 16-50 F/2.8 and 50-135 F/2.8.

For non SDM lenses, it works pretty well, including with the Tamron 18-250 f/3.5-6.3 at the long end.
11-21-2012, 04:29 PM   #7
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The Kenko 1.5 PZ-AF Teleplus TC is good, and will deteriorate IQ very little if you start with a good lens such as the Tamron 70-200.

AF is great with screw drives lenses.

My experience with the TC and SDM and HSM AF is similar to the statements above - I use manual focus mode when using it with SDM or HSM lenses.
11-22-2012, 11:30 AM   #8
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QuoteOriginally posted by crewl1 Quote
The Kenko 1.5 PZ-AF Teleplus TC is good, and will deteriorate IQ very little if you start with a good lens such as the Tamron 70-200.

AF is great with screw drives lenses.

My experience with the TC and SDM and HSM AF is similar to the statements above - I use manual focus mode when using it with SDM or HSM lenses.

Any thoughts on the Kenko 1.5 PZ-AF teleplus converter mentioned above versus Kenko 1.5 DG AF teleplus converter? What is the difference?

11-23-2012, 10:42 AM   #9
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QuoteOriginally posted by larshalvar Quote
Any thoughts on the Kenko 1.5 PZ-AF teleplus converter mentioned above versus Kenko 1.5 DG AF teleplus converter? What is the difference?
I've only tried the PZ-AF, but from pictures it appears the DG does not have the SDM contacts? Looking at KENKO DG AF 1.5 X TELE CONVERTER FOR PENTAX LENSES DIGITAL SLR | eBay
11-23-2012, 07:53 PM   #10
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That's correct. Pz-AF has the power zoom contacts, which are also used for SDM. The DG version lacks these contacts.

Also worth mentioning: the currently-available Vivitar 1.4x TC is supposedly the same optics as the Tamron 1.4x but lacks the SDM contacts.
11-24-2012, 06:17 AM   #11
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QuoteOriginally posted by msatlas Quote
That's correct. Pz-AF has the power zoom contacts, which are also used for SDM. The DG version lacks these contacts.

Also worth mentioning: the currently-available Vivitar 1.4x TC is supposedly the same optics as the Tamron 1.4x but lacks the SDM contacts.
Does this then mean that it is not compatible with the tamron 70-200? I think I recall that in an earlier post it was stated that tamron themselves did not recommend using them together.
11-24-2012, 07:46 AM   #12
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You need the Pz/SDM contacts to have AF with a lens that has its own focus motor rather than the one in the body. That's Pentax SDM & DC lenses, Sigma HSM & Tamron USD (which I don't think there are any Tamron USD lenses for Pentax yet).

The Tamron 70-200 should work with most any 1.4x or 1.5x AF TC, since it uses regular screw drive AF and any AF TC will support screw drive. With these TCs you lose one stop of light so the Tamron 70-200/2.8 becomes a (roughly) 100-290/4.

When you use a 2x TC, you lose 2 stops of light. So an f/2.8 lens becomes an f/5.6-equivalent lens. The camera may have some difficulty with AF in this situation.

Also worth noting: none of these TCs change the focal length of the lens that's reported to the camera, which makes SR less effective. The camera thinks it's got the original focal length lens and SR functions based on focal length. But really the lens is 1.4x (or whatever TC you have) longer. This is less relevant if you're not hand-holding anyway.
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