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Old Sep 11, 2008, 2:21 PM   #1
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I am fairly new to dslr and have bought a Tamron 2x Tele Plus.

If I try to use it on my 70-300 lens it doesnt seem to work when the lens is in zoom mode.

I have used it with a fixed lens and its ok but when I try to zoom it will not focus on af or manual.

I took it to a friend who is actually very experienced and he said he didnt know why it didnt work and even tried his own lenses but the same as in the fixed lenses were ok but try to zoom and it didnt work.

Any help would be appreciated.
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Old Sep 12, 2008, 4:44 AM   #2
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joneos wrote:
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I took it to a friend who is actually very experienced and he said he didnt know why it didnt work and even tried his own lenses but the same as in the fixed lenses were ok but try to zoom and it didnt work.

Any help would be appreciated.
LOL, obviously not experienced enough but you are in the right place now :-)

Welcome to Steve's btw, we hope you get a lot out of the forums here!!

OK, this is very simple, with a 2x Tele Converter (TC) you will lose two stops of light and this is where the problem is. A Canon dslr needs you to have more than f5.6 (f8 for a 1D)to focus so if the original lens is less than f2.8 it will then be too dark for the camera to be able to focus. I'm guessing your fixed (prime) lenses are f1.8 which means they allow enough light into the camera even with the 2x TC.

You are not the only one in this boat so unfortunately you will need to MF the lens with the 2x TC fitted and there will be quite a noticeable reduction in quality, everything is a trade off.

Do get involved in the forums as many of us have learnt lots through here, we have sections for posting photos as well as discussing specific camera's/lenses etc. What sort of photography do you enjoy most?

Happy shooting,

Mark
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Old Sep 12, 2008, 7:15 AM   #3
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You may be able to get it to AF by taping over some of the contacts (so that the camera doesn't know what aperture the lens has available).

See tip number 1 for the tape trick (which contacts to tape over). The same thing would probably apply to your Tamron TC.

http://www.fredmiranda.com/TipsPage/

The Teleplus is a "smart" TC, so it's reporting corrected Aperture information to the camera (which is great if you want that, but bad if you need Autofocus trying to use a TC on a lens that dim).

Because of the light loss through a 2X TC, the camera will probably struggle to lock focus in less than optimum lighting, especially on the longer end since your lens loses light as you zoom in more. But, you may be able to coax it into focusing in good light if you tape over the appropriate TC contacts.

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