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03-08-2011, 05:40 PM   #1
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Which TC should I buy?

I do not understand what I need to consider when buying a tc for my Pentax K20D. Some of the on-line discussions seem to indicate that I might need a different tc for each lens.

I use the following lenses: DA 15mm f4 ltd, DA* 55mm 1.4, and DA* 50-135 f2.8. I want to increase my camera's reach especially with the 50-135mm lens and get close-ups of wildlife or athletes.

What brands and magnification do you recommend?

Thanks,

Ed

03-09-2011, 05:47 AM   #2
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Both Pentax and third party teleconverters are reviewed in the Lens Review section, so you might want to look there for info.

Pentax Teleconverters

3rd Party Teleconverters

Remember though that there are different types of teleconverters, just like there are different kinds of lenses. You will most likely want one that has all the electrical contacts to enable your lenses to work properly, as opposed to the older mechanical ones. You also need to decide on magnification factor.

Pentax makes two that are lens specific: Converter-A 1.4x-L and Converter-A 2x-L and these will not work with your lenses. The Sigma two listed in the reviews are also lens specific.

All teleconverters will reduce light, thus decreasing the effective F stop of your lens, which will become an issue in low light situations.
03-09-2011, 06:38 AM   #3
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QuoteOriginally posted by bonaprof Quote
I use the following lenses: DA 15mm f4 ltd, DA* 55mm 1.4, and DA* 50-135 f2.8. I want to increase my camera's reach especially with the 50-135mm lens and get close-ups of wildlife or athletes.
I'll take a quick stab at this.

Although I've never tried, I can't imagine you'd every want to use a TC with the DA15.

For the DA* lenses, there are really only two options unless you want to go fully manual focus.

With the DA*55 and DA*50-135, there really aren't any TCs that will retain complete use of autofocus system.

The Tamron 1.4x Pz-AF is optically pretty decent and will allow you to (somewhat) retain AF, but it's a less than perfect solution as it's hesitant to lock on the first try and usually takes several tries (pre-focusing close and then locking helps a little). The Tamron 1.4x is no longer sold new and the price of a used one is typically around $160-180. I believe there is a Kenko 1.5x that is suppose to be very similar which also sells for around the same price, maybe a couple dollars less. I've never used the Kenko so I can't personally say how it works with the DA* lenses.

There is also the Pentax 1.7x AF-A. Using this, you would need to prefocus the lens close to the proper focus distance and then you engage the AF of the AF-A. In this case, you never actually use the SDM motor of the DA* lenses as all the focusing is done inside the AF-A (screw drive). You can also use this on any lens, included manual focus lenses, to get a "semi-AF" lens. The price of the 1.7x is usually around $300-350 used.
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