Sigma APO 120-300 f/2.8 and Canon extenders

[StewartR]

Does anybody know whether the Sigma APO 120-300mm f/2.8 EX DG is compatible with a Canon EF Extender (1.4x or 2.0x)? It looks like it ought to be - the rear element of the Sigma is deeply recessed - but I'd like to hear from someone who has practical knowledge rather than just theoretical analysis.

If it does fit, what is the IQ like? Would it be better (much better?) to use a Sigma teleconverter instead?

[SDK^]

The Canon extender fits because I was standing next to someone with one fitted on Saturday.
I guess image quality is much the same.

[tappilappi]

Hi, I have one of these lens, as well as both the canon and sigma extenders. I must admit that I tend to use the sigma extender on my sigma lens, and the canon extender on my canon lens - no particular reason why :shrug:
The canon extender does fit, and when I have used it with the 120-300 I have not noticed any difference in picture quality.

http://farm3.static.flickr.com/2299/2401849272_981fe5d1d1.jpg

[StewartR]

Wow, that seems pretty conclusive! Thanks tappilappi. And thanks alsi to SDK^ for another helpful answer.

[stylgeo]

Hey Stewart,
Having bought this lens just recently, i opted to buy the Sigma TC aswell. The reviews I read about it was that, while the 1.4x gives the same result from both manufacturers, the Canon 2x doesn't work that well with this lens, giving worse IQ and focusing speeds than the Sigma 2X.
I haven't tried it myself but I must say that with the Sigma 2x, even if the results are softer the photos are still quite usable.

This is a sample of the 120-300mm +2X TC 100% crop.

This is straight from the camera, with sharpening set to 0 (zero)
http://www.avforums.com/forums/attachment.php?attachmentid=76949&d=1206922219

This is after some slight sharpening (Unsharp Mask, 1px 85%)
http://www.avforums.com/forums/attachment.php?attachmentid=76950&d=1206922252

[Les McLean]

Posted a thread giving examples of 120-300 f2.8 with Sigma 1.4 TC, 2.0TC and 1.4 and 2.0 TC stacked (all on 1Ds MKII)

http://www.talkphotography.co.uk/forums/showthread.php?t=55242