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Old Jun 19, 2012, 2:24 PM   #1
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Default Teleconverters

I have two lenses, both Tamron, for my Sony A580. One of my lenses is a Tamron 18-250. Will a teleconverter work with this lens? If so, could someone recommend one? Thanks in advance for all helpful advice.
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Old Jun 19, 2012, 3:10 PM   #2
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The 18-250 isn't very bright at the long end (which is where you would want the t/c anyway) and the light loss would likely make autofocus difficult in any but very bright light. I don't think I would use that combination.

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Old Jun 19, 2012, 5:37 PM   #3
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G'day mate

Gotta agree with VT here
> with the max aperture of f5,6 or therabouts when at 200mm plus, by the time you lose 2-stops from the TC, focussing at f11 is a non-event and
> with a dozen or so glass-elements already in use, the adding of another 4 or 5 in the TC will degrade IQ considerably
"experience talking" here

However - if you do want to play with 500mm stuff, hunt around for a 2nd-hand 500mm MTO lens for $150-200 [talk to Streets here > he seems to find them !!!] and have a play with something like that

Hope this helps a bit
Regards, Phil
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Old Jun 19, 2012, 5:53 PM   #4
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A 2X Teleconverter adds 2 stops to the maximum aperture of a lens. Any lens with a maximum aperture of f/4 or smaller won't autofocus when used with a 2X teleconverter.

A 1.4X Teleconverter adds 1 stop to the maximum aperture of a lens. Any lens with a maximum aperture of f/5.6 or smaller won't autofocus when used with a 1.4X teleconverter.

Your Tamron 18-250 has a maximum aperture of f/6.3, which means that, whatever teleconverter you use it with, it won't AF for some portion of its zoom range.

If you're ok with that, remember also that, while 1.4X teleconverters in general aren't bad, cheap 2X teleconverters are pretty awful, and your lens has a significant amount of CA on its own. Plus, you can't use that lens with a good matched teleconverter.

If you need something longer than you get with the 18-250, I think you need to start over.
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Old Jun 19, 2012, 7:54 PM   #5
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+1 on the comments so far.
The combination is not good.
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Old Jun 19, 2012, 8:02 PM   #6
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Agreed, you need fast, sharp glass with TC's...

I do use mine with my macro to increase magnification but I also manual focus most
times I do that...
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