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10-28-2007, 03:41 AM   #1
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Is this a teleconverter or a tele-photo lens?

Hi

I stumble upon this ebay ad:

52mm 2X Telephoto Lens Fits Pentax K100D K110D ist DL - (eBay item 250178710070 end time Oct-28-07 10:40:11 PDT)

Is this a teleconverter or a lens?

Thanks

10-28-2007, 03:53 AM   #2
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It's a 2x multiplier. It screws on the front end of a lens that has 52mm filter thread. Will it multiply? Yes. Will it be any good? Not that great? The images will be much softer than the lens it's mounted to. I bought a similar set for my Kodak P&S (came with a wide version and a 2x version together in a package) After trying the 2x a couple of times I tossed the 2x. The wide works pretty good and the DOF is much greater at the wide end and compensates a bit for the loss in image quality. Haven't tried either on a DSLR but I'd have to assume you'd be disappointed and would get rid of it in fairly short order.

IMO there are no cheap solutions when it comes to glass. If you can't afford a longer lens now then save up till you can get what you want. Alternatively you can add a good Sigma or Tamron 1.4x rear converter and there are a couple of Pentac 2x versions on the used market that are much better than the unit above.
10-28-2007, 03:55 AM   #3
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Neither, and both at the same time
It sits on the front of your lens, via its 52mm screw thread.
It multiplies the effective focal length of your lens by 2x.
Past experience would indicate it will suffer badly from flare and give a soft image.
YMMV
10-28-2007, 04:24 AM   #4
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Thanks for the help! Appreciated!

10-28-2007, 09:43 PM   #5
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I was wondering if these teleconverters were any good. I keep seeing them on eBay both as a stand-alone auction and combined with many digital cameras. What always bothered me about these lenses is it added mass at the end of the lens which could interfere with focusing and put an extra load on the focusing motor. I definitely do not want to burn up my camera focusing motor with these converters.


joe1955
10-29-2007, 04:33 AM   #6
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Would not normal teleconverters (installed in between the lens and the body) also present an extra load to the focusing motor?
10-29-2007, 09:32 AM   #7
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QuoteOriginally posted by raider Quote
Would not normal teleconverters (installed in between the lens and the body) also present an extra load to the focusing motor?
Physics tell us that anything at rest tends to stay at rest, anything in motion tends to stay in motion.

In order to start something moving we must apply a force to the object equal to the speed that we wish to achieve, in order to stop the object we need to place an equal but opposite force to the object.

The shaft going through a normal tele-converter is very light and easy to move. The lenses that I have seen on eBay would have a very large mass in some cases several thousand times that of a small shaft.

In this case there would be a rotational force suddenly applied to this mass, and then an equal force suddenly applied to stop it. Over rotation would probably be a problem forcing the lens to change directions to compensate adding more of a load to the motor. This would at least shorten the life of the batteries, the worst thing that could happen is it could damage the camera.

The only rear mounted tele-converter that I know of that moves any lenses within the tele-converter, is the Pentax teleconverters that would convert a manual focus lens to autofocus, "these lenses are no longer available from Pentax, although I have seen them on eBay, they go for about $350 each.

I would rather spend my money on a good autofocus lens.


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10-29-2007, 01:47 PM   #8
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For what it's worth, there ARE some 2X extenders like this one that do a good job. But like anything, you get what you pay for. Century Optics makes excellent wide angle and telephoto adapters. Their 2X converter that's around this size is selling for $399 at B&H. You may be asking yourself why anyone would pay that much for an adapter when they could easily just buy a longer telephoto lens. It's because the Century adapters are really intended for use on video cameras where a zoom lens can cost as much as $12,000. From that viewpoint, a $400 adapter than can extend the range of your lens starts to look like a bargain.

10-29-2007, 05:08 PM   #9
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Thanks for the replies. I understand now.
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