1.4 or x2 convertor

kevstar

kevstar

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kevin
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Hi thinking of buying one of the above converters to go with my canon 40d and sigma 100-300 f4 lens mainly to be used for Motorsport. Would be good to get some advice on the ups and downs of having one also which make to go for. Thanks in advance
 
kevstar said:
Hi thinking of buying one of the above converters to go with my canon 40d and sigma 100-300 f4 lens mainly to be used for Motorsport. Would be good to get some advice on the ups and downs of having one also which make to go for. Thanks in advance
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Only buy the sigma 1.4x TC, you won't be able to autofocus with the 2x TC. Remember that you lose an f-stop of light, so your lens wide open will become a 140-420mm f5.6

You'll have to be more careful focusing on your target, as loss of autofocus will cause the lens to hunt and it will be slower to regain focus, however, should be no visible loss in image IQs, I've had very good success with the canon 300mm f4 and 1.4x TC with motorsport and wildlife.

2x TC won't autofocus, manual focus only, loss of 2 f-stops of light, so 200-600mm f8 and you will start to see loss of detail in image IQs, so decision is yours
 
As pete has said, any body that isn't a 1D won't AF with a minimum lens aperture of f/8 or above.
There are ways to trick lesser bodies into autofocusing (taping over some of the pins on the TC) which can sometimes work fairly well. However, you've mentioned motorsports, and if there was ever a time where fast and accurate AF was needed, I'd guess this was it. In which case, I'd recommend certainly no more than the 1.4x!
 
I've got a Kenko Pro300 DGX 1.4x TC and that allows a Canon 100-400 f4.5-5.6 IS L to AF on a 550D, 7D and 5D2 as I've tried it. In good light the AF seems as fast as usual and it doesn't keep hunting for AF until the light drops dramatically.
I use the TC regularly on a 70-200 f2.8 IS L and the IQ is excellent when stopped down to f5.6-8. There is no Sigma lenses listed on the compatability list for the Kenko TC's at the moment, although I've used my Sigma 150-500 OS with the Kenko, but only in MF as the AF will not function at all with the TC.
 
Thanks for the info now thinking if I'd be better just keeping with the setup I have. Its still early days with this lens so maybe better trying to get closer and get shots I'm happy with.
 
When I had the 100-300mm F4 I used the 1.4x with it too. There was a drop in autofocus speed but accuracy was retained. The difference in quality was marginal!
 
modchild said:
I've got a Kenko Pro300 DGX 1.4x TC and that allows a Canon 100-400 f4.5-5.6 IS L to AF on a 550D, 7D and 5D2 as I've tried it. In good light the AF seems as fast as usual and it doesn't keep hunting for AF until the light drops dramatically.
I use the TC regularly on a 70-200 f2.8 IS L and the IQ is excellent when stopped down to f5.6-8. There is no Sigma lenses listed on the compatability list for the Kenko TC's at the moment, although I've used my Sigma 150-500 OS with the Kenko, but only in MF as the AF will not function at all with the TC.
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This is my understanding of how things work:
Reporting TCs (Canon I & II, Kenko DG, Sigma): A TC-compatible lens (e.g. 400/5.6) detects the presence of a TC through the 3 extra contacts and reports the correct f-stop for the combination to the camera. If the f-stop is above f/5.6, AF is disabled for non-1-series bodies.

Non-reporting TCs, or taped TCs, or TCs with non-TC-compatible lenses: The lens does not detect the TC and just reports its own f-stop. AF may still work, because the camera doesn't know about the true f-stop, and tries to AF even if the combination is outside the specs.

Kenko DGX: Unlike the above TCs, the DGX manipulates the communication between the lens and the body so that the f-stop is always reported correctly for the combination, and so that AF is retained even if the combination is above f/5.6. From your and others observations that f/8 is reported but AF still works, my guess is that wide-open f-stop and used f-stop is reported separately and the camera looks at the wide-open f-stop to determine if it should try to AF.
 
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