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03-28-2010, 11:14 AM   #1
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Teleconverters

I have had Pentax and Ricoh 35mm cameras for many years and have a small collection of old lenses and a 2x Teleconverter. I recently purchased a Pentax Kx dSLR with an 18-55mm and an 55-300mm lenses. The 2x teleconverter works well with this setup when used on manual focus but despite the fact it appears to have sufficient electrical contacts in the right places it does not work with auto-focus. Granted the teleconverter is very old so I'm not too bothered by this.

I have two questions:-

1. Do more modern teleconverters allow the aotofocus to be used?

2. I recall seeing 4x teleconverters many years ago for pentax lenses. Google didn't help me. Are there any 4x teleconverters compatible with my new lenses.

Any help gratefully accepted...

03-28-2010, 11:25 AM   #2
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I don't have much experience with teleconverters but bought a Quantary 2X from TechForLess because it was so cheap ($22.46 USD). It does work for autofocus. I haven't had a chance to really try it out yet as far a image quality goes.
03-28-2010, 11:27 AM   #3
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Modern tc's do suport AF. But they don't necessarily produce better results than simply cropping, and in fact generally do noticeably worse - plus you lose a stop or two of light. Some specific lenses with some specific TC's can perform better than cropping, but in general, the kit zooms are virtually never improved by a TC - you're almost always better off simply cropping.
03-28-2010, 11:34 AM   #4
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Thanks for the rapid responses.

I'm aware of the light issues and generally only shoot on very well lit days. The reason for the need for using teleconverters is because I enjoy wildlife photography, (specifically "portraits"), so it is more an issue of distance from the subject rather than cropping out unwanted subject matter and hence my additional interest in a 4x converter to really be able to "reach out". My other alternative is an even longer lens which, at the moment, isn't a viable option.

03-28-2010, 02:50 PM   #5
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you could use a 4x teleconverter but to give you more distance but they are hard to come by. You can stack two 2x teleconverters together. However, you'd lose so much light that you might as well give up.

If you looking to get into the 1200mm range with the 4x and the 300mm zoom lens you have. You would be looking at a F24 or around there. Which would make the lens pretty much useless in most lighting conditions and also the Shake reduction would be ineffective I'd have to guess.

If you are looking for 500 - 800mm range and want to keep cost relatively low. You should look into mirror lens. Or perhaps get a really really fast 300mm lens then you'd not have to worry about light loss as much.
03-28-2010, 04:36 PM   #6
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QuoteOriginally posted by GingeM Quote
The reason for the need for using teleconverters is because I enjoy wildlife photography, (specifically "portraits"), so it is more an issue of distance from the subject rather than cropping out unwanted subject matter
Same thing. Try it some time. Increasing focal length is no different from cropping in their basic effect, which is to make your subject larger in the frame. Sure, cropping means losing resolution along the way way, but my point is, the same is true of most kit lens +TC combinations. Using the TC gives you an image that looks exactly the same as the image you get by cropping - until you zoom in and realize the TC image looks worse.

QuoteQuote:
My other alternative is an even longer lens which, at the moment, isn't a viable option.
A 500mm mirror lens will cost no more than a TC. I don't have the 55-300 but rather the 50-200, and I've tried using it with a 1.5X TC (which should degrade the IQ less than a 2X or more TC). The 50-200 + TC does *not* perform better than simply cropping, but on my camera at least, the $100 Samyang 500/8 mirror lens that is sold all over Ebay under a variety of names *does* beat simply cropping the 50-200, if not by a lot.
03-29-2010, 02:38 AM   #7
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Thanks for all the input. I'll have a look at the cropping and a look at mirror lenses. Probably be back with more questions too...
03-29-2010, 04:20 AM   #8
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Tele converters for sport

I am an avid field hockey Player and spectator. I recently purchased a Sigma 70-200 f2.8 for this purpose. Combined with the greater pixles of the k7 over the *istD has given me some great results. This lens gives me excelent results to 25m after which I am cropping. At 50m I am cropping 3/4 of the photo.I am wondering how I am going to go at events where I am going to have to be a good 25 metres away from the side line. (much to some umpires disgust I am sometimes almost on it. all for a good shot) Would a 2x tele converter be the go here? if so would I be better off buying a Sigma to go with the lens? Perhaps I would be better off with a larger focal length lens.

James

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