Converters

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51
Name
Phil
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#1
I've decided to get a Sigma 18-250mm F3.5-6.3 DC MACRO OS HSM lens.

A question with regard to this lens can you add a x2 teleconverter and is there any "rules" around converters.

I understand same makes with same lens but why would you go for a x1.4 over x2 teleconverter
 
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3,104
Name
Julian
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#2
You will find that you will lose autofocus with that setup - the converter drops the amount of light hitting the sensors (image and autofocus sensors).
You can only really use converters on faster lenses like the 70-200 f2.8

I have the Sigma 1.4 and it works perfectly on my Sigma 70-200. It will work on my 120-400 but I lose autofocus. I did have the 2x and again worked only on the faster lenses.
You will also lose image quality to some degree. The 1.4 is pretty good but the 2x was quite bad I found - was all a bit soft and fuzzy.
Hope that helps a little:)

Edit - the 1.4x will lose 1 stop of light and the 2x will lose 2 stops of light

Edit - also regarding your other post, this lens is not a true macro lens and will not give you 1:1 reproduction ( where the subject is projected as life size on the image sensor) - you may be a little disappointed

Edit - see this page for sigma teleconverter compatibility - http://www.sigmaphoto.com/teleconverter-compatibility
 
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545
Name
Dan
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#3
Teleconverters are best used with prime lenses or fast/high end zooms- I wouldn't even try with this lens for reasons Julian states.
 
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Spavo
Messages
51
Name
Phil
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No
#4
Thanks, guys I didnt know you would lose the autofocus with these set ups , the lens i'm going to use as a replacement for my 18 -55mm & 70 - 300mm cannon lens.

Awaiting a refund and then going to get 150-500mm sigma and was thinking about get a converter as would have two lens. Butgoing to keep my hands in my pockets.
 
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3,104
Name
Julian
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#5
Yeah the converters won't work on the 150-500 either - it's essentially the same lens as my 120-400 with a different front element setup.
I don't even try to use the 1.4 on my 120-400 lens as there is a definite drop in image quality which is odd because on the 70-200 there's almost no drop in quality. That and losing AF makes it pointless with that lens.
 
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22,943
Name
Richard
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#6
Yeah the converters won't work on the 150-500 either - it's essentially the same lens as my 120-400 with a different front element setup.
I don't even try to use the 1.4 on my 120-400 lens as there is a definite drop in image quality which is odd because on the 70-200 there's almost no drop in quality. That and losing AF makes it pointless with that lens.
All a telecon does is enlarge the image coming through the mother lens, so there is always a loss of sharpness. The more resolution asked of a lens, the less sharp the detail becomes, and telecons ask a lot. But if you start with a very sharp lens, you can still end up with a decent result. 90% of the IQ with a telecon is down to the mother lens.
 
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