# Canon D30, Sigma 300-800 and teleconverter



## Kevin Barrett (Apr 26, 2007)

My wife has a Canon 30D and a the Sigma 300-800mm Zoom lens. I would like to get a 2x teleconverter for it but I want it to retain the auto focus capability throughout the 300-800 Zoom range.

Is there a teleconverter that will do this? Sigmas will not (and I don't think Canons does either).

Thank you in advance.

Kevin


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## YellowBay (May 7, 2007)

Hi Kevin,
Niiiiiice Lens.
I don't think anyone does a converter for that lens which supports AF. In addition, the converters push the f values up to F8 for the 1.4x and F11 for the 2x. That makes for a pretty slow lens. Having said that, I'd go for it anyway. What are you planning to shoot? 

This might help.
http://www.sigma-photo.co.jp/english/support/faq/condaitr.htm


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## Big Mike (May 7, 2007)

Welcome to the forum.

It's not the teleconvertor itself that is the weak link...it's the camera.  The camera needs a minimum of F5.6 (that amount of light) for the AF sensors to work.  A TC, effectively steals light...so when you use the teleconvertor, you no longer have enough light for the AF sensors to work.  

I think that the top end Canon bodies have more sensitive sensors which can focus with less light...but not the 30D.

Another thing to consider is that a TC will also steal some image quality.  With that great lens, you might be better off to just shoot and crop rather than use a TC.


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## lostprophet (May 7, 2007)

if you had a Canon EOS 1D or 1DS series body if would focus with a 1.4x converter with the middle focusing point


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