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Old Feb 23, 2009, 5:08 PM   #1
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Does anybody know what brand of 1.4 tele converter would work on my a100 with a Sigma 70-300 4/5.6 DL Macro Super II and Minolta 70-210 f4 "beercan"? Thanks for your help!
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Old Feb 23, 2009, 10:42 PM   #2
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Except for the Sony and Sigma teleconverters (that won't work with your lenses anyway,) all teleconverters are made by Kenko regardless of the brand on the barrel. And they are generic, meaning they'll work with any lens.
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Old Feb 24, 2009, 9:24 AM   #3
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A note of caution about teleconverters:

In addition to increasing the focal length of a lens, because aperture is a function of focal length, a teleconverter will decrease the maximum aperture of a lens. Sony dSLRs won't autofocus with any lens that has a maximum aperture smaller than f/7.1. When you put a 1.4x teleconverter on your 70-300 f/4.0-5.6, it will become a 100-420mm f/5.6-8.0, so there's a good chance the autofocus system will not work at the longer focal lengths.

The reason I say "there's a good chance" is because it depends on the teleconverter. Kenko makes teleconverters that are 'chipped' and teleconverters that are not. Lenses tell the camera what focal length and maximum aperture they have. The cameras use this for the autoexposure system and the SteadyShot sytem, as well as storing that info in the EXIF data for each photo. A 'chipped' teleconverter will adjust the focal length and maximum aperture so the camera gets accurate data for its systems, but with your 70-300, the camera will learn that the maximum aperture of your lens is f/8.0 at the long end, and will refuse to autofocus. Most 1.4X teleconverters aren't 'chipped', however, so the cameras wouldn't know about the change to the maximum aperture, so they wouldn't know enough not to try to autofocus, but they also wouldn't know the correct focal length so theSteadyShot systemwouldn't be able to properly compensate for camera shake. It also wouldn't report the correct focal length and aperture in the EXIF data.

The Sigma is a relatively dim lens anyway, so you shouldn't expect to be able to autofocus with a teleconverter, whether it was 'chipped' or not. Your Beercan should work fine either way, but a 1.4X teleconverter on the Beercan will make it a 100-295mm f/5.6, which isn't a lot different from your Sigma.
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Old Feb 24, 2009, 9:24 AM   #4
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Thanks tcav, I was hoping you'd answer. I consider you the go to source for info, especially for Sony products. I'll pick up a Kenko.
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Old Feb 24, 2009, 9:25 AM   #5
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We posted simultaneously. Please read my second post before you do anything.
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Old Feb 24, 2009, 9:26 AM   #6
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donp wrote:
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Thanks tcav, I was hoping you'd answer. I consider you the go to source for info, especially for Sony products.
Thank you for those kind words, but I assure you that I'm standing on the shoulders of giants, some of whom are right here.
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Old Feb 24, 2009, 9:30 AM   #7
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You're right, I'll give this some more thought, I just figured that the beeercan is a better lens than the Sigma, so even if it ends up the same, I'd have a better lens at the 70/300 range.
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Old Feb 24, 2009, 11:01 AM   #8
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donp wrote:
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...I just figured that the beeercan is a better lens than the Sigma, so even if it ends up the same, I'd have a better lens at the 70/300 range.
One of the unfortunate consequences of using a teleconverter, especially a generic teleconverter, is that it will reduceimage quality, sometimes considerably. I have a Quantaray 2X teleconverter that I have taken to calling 'The Purple Fringe Machine'. I also have a Rokunar (Kenko) 1.4X 'chipped' teleconverter and a Cambron (Kenko) 1.5X 'unchipped' teleconverter that I've mostly been pleased with, but I don't have any lenses with maximum apertures smaller than the Beercan's f/4.0.
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