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04-27-2010, 07:56 AM   #1
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question on TC use with long zoom lenses

I decided that I need something in the 300-400mm range...

Pentax only has the 55-300, which if it were a bit longer would fit the bill. It is too slow to use with a TC.
My other choices are:
  1. Tamron 70-200mm f2.8 with a 2x converter from sigma or Tamron
  2. Sigma 120-400mm 4.5-5.6
  3. Sigma 100-300 f4 with 1.4 converter
Does anyone have any idea about the compatibly of the Tamron 70-200 with 2x converter in terms of AF, aperture control,etc with the K7? will either the tamron or Sigman TC support HSM?

Thanks for your input

04-27-2010, 02:06 PM   #2

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From what I know, currently there is no 2X TC that supports Pentax SDM (or HSM as Sigma calls it).

Some 1.4X or 1.5X TCs (Tamron, Kendo) "kind of" work with SDM but not fully. I have a Tamron 1.4X TC. When used with SDM zoom lenses (DA* 60-250 and DA*50-135), at the long end, it hunts back and forth a lot.

The only TC I'm currently using is Pentax 1.7X AFA.
04-27-2010, 03:52 PM   #3
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tc on pentax 55-300

i use a tamron 1.4x pz-af mc4 af converter or a kenko p/af 1.5x teleplus mc on the 55-300 pentax. i have even use the tamron on a sigma 170-500 apo dg. if the lens has trouble af, i mf the lens. after i mf the lens, i turn on the af on the camera.
04-27-2010, 04:54 PM   #4
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I have the 55-300 and took a bunch of surfing pics one day. They turned out ok. For the last 40% or so I used an albinar-adg auto 2X and the pics were washed ouit pretty bad. It was my first time trying it that way. If I had added some negative ev it might have helped, but...

Since then my focus ring on the 55-300 started grinding a little. Once I get a spare minute I'm going to contact Pentax about it, and maybe send it away for a look. It's only about 5 months old.

I picked up a promaster 100-300 that has better colors than my pentax, and use that more often. I also picked up a telesar 300 f4 from a pawn shop, and that beats both of them, but it's not a zoom, so it's limited for me.

The converter is a k/r model that I got with a lens off ebay, essentially for free. What's that old saying, you get what you, won't get fooled, knock three times, I don't know. Anyway, it's ok for education purposes.


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