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06-01-2009, 09:32 PM   #1
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What are 2x converters used for?

What are 2x converters used for and how many different types are there?

06-01-2009, 09:44 PM   #2
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2x converters are like other teleconverters used to extend the focal length of a lens.
a 2x converter will make a 100mm lens into a 200mm lens at the cost of 2 stops of light so a 100mm f2.8 becomes a 200mm f5.6.
1.5x converters are more common because they normally yield better results than 2x converters.

a converter will normally degrade the optical quality of the lens, the better and normally, the lesser the power of the converter and the better it is, the lesser degradation. also the better the original lens is the lesser you will notice the degradation.

so taking a so so lens and putting a 2x converter on it will normally yield pretty bad results.

i dont personally know of any 2x converters that are good eanough that i would put them on any of my lenses. 1.4/1.5 converters seem fine though.

remember you also loose light and if you loose too much light then the auto focus will likely not be able to work anymore because its too dark for it. for example if you put a 2x converter on a f5.6 lens.

there are different types available with different magnifications such as 1.4 1.5 1.7 2.0.
some are general tc's and some are matched either to certain lenses such as some long teleportos that come shipped with specially matched tc's. some are matched to types of lenses like sigmas ex converters matched for their ex series of lenes. pentax used to have 2 types 1 for shorter lenses and 1 for longer.

normally a tc will have a compability list because it might not be functional with all lenses due to the distantce of the rear element of any given lens, some might clash with the glass in the tc.

also tc's have different number of contact pins on them, like lenses do if you look at the back. if the tc has fewer contacts then the lens you will loose some functionality for example SDM doesnt work through all tc's.

also, some tc will report the focal length and aperture to the camera while others will not, if the tc doesnt do this then if you use a 2x tc on a 100mm lens the camera will think its still a 100mm lens and a not a 200mm one.

finally, pentax doesnt currently make and tc and they havent for a while. they had an SDM tc on their lens roadmap, supposedly it was supposed to be 1.4x but they removed it when they updated the roadmap, I guess sadly it has low priority.

using tcs with fast teles can be a good idea, for example if I had the pentax da 200mm f2.8 then Id rather get a 1.5x converter for it, making it 300mm f4, instead of buying the pentax da 300mm f4 in addition.
06-01-2009, 11:25 PM   #3
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I use a Quanteray 2x converter and all of my information is retained in the camera.

However, I have trouble auto focusing with my Tamron 50-300 f/4-5.6-mm lens; it just goes in and out.

So I switch to manual focusing.
06-02-2009, 04:35 AM   #4
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thanks guys for explaining it

06-03-2009, 01:57 PM   #5
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That is why you would also see the 1.4X TC's selling for much more than the 2X TC's as the 2X TC's are usually not that great if you have a not so great lens that isn't usually a fast (large aperture) prime lens or a fast (large aperture) zoom lens.
06-03-2009, 05:19 PM   #6
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QuoteOriginally posted by Ajr901 Quote
What are 2x converters used for and how many different types are there?
They make excellent paperweights.
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