Sigma 120-300 f2.8 & extender question.

Hi, I'm very close to ordering this beasty. From other threads I've read I have come to the conclusion that this lens is a great performer.

Only thing I would really like to know is

a) what is the autofocus like compared to canon USM?

b) How does it perform with t'cons? I'm thinking of getting both the Sigma 1.4 and 2x converters for a max 600mm f5.6

Lastly, will the canon mkII 1.4 extender work with the Sigma?

Anyone with a link to shots taken with the 120-300 + 2x converter would really make my day

Here's a review on the lens and he talks about use with a TC, 1.4 and 2.
http://www.press-photos.com/html/review​s/sig120300.html?3

1.4 was said to be fine, but 2 is not worth it, unless you have one already.

According to this review, Canon extenders do work with it. I am going to get this lens soon, and apparently going to try my 2x tc out on it i guess.

In my experience there is no difference worth worrying about between HSM and USM on these long lenses. With the 20D you'll get better AF performance with 2.8 lenses too. If I was buying this lens I'd get a 1.4x and maybe look for a SH 2.0x to just try it, or borrow one if you can. I've never got good enough results with a 2.0x on these kind of long lenses. The Canon should work as they are essentially identical to the Sigma design. Check out pbase and photosig for shots ... you might be lucky tho' maybe a small user base of this combo

Well there is nothing to compare........ There is no zoom like this one.

Only if we are looking at 300 vs 300, could we compare, and I'd take the 300 2.8L over the Sigma generally. But hey, I'm just a poor college student! And it's too hard to run off with a 300 2.8.

Focus speed.... the Sigma 120-300mm f/2.8 EX is faster than a Canon 100-400mm f/4.5-5.6L IS USM but not quite as fast as a Canon EF 85mm f/1.8.

Extenders.... it works very well with a 1.4x with a barely noticeable drop in quality. The optics are acceptable with a 2x extender but the focus speed is too slow for sports work in that configuration. The results are slightly more pleasing with the Sigma 2x TC than the Canon one.

Oh, and yes, the Canon 1.4x extender will work.

am i right in thinking that with a 300 and 1.6 crop thats 480mm so will a 2 x conv give a focal of 960 mm

Yes, you'd get a field of view of that. That's correct. I'd still try and avoid the 2x though. 960 is a lot so you'll defintely be peeking in someone's window with that distance.

so you get 672mm with a 1.4 conv
if you used a smaller lens ie: a 200mm with a 2x are you still going to loose as much quality as using it with the 300 or is it the same.

Using a 2x converter in general will cost you quality. I don't believe anyone's ever done a lens-by-lens study that "with a 2x TC on lens A, you'll lose 19.5% IQ while with lens B, you'll lose 21.3". Among other things, the comparison would have to be able to adjust for different performance by the unconverted lenses. The closest you'll find is in Canon's EF Lenswork book, which has MTF tests for all the (then) current lenses, and includes results with TC for those that do support the Canon TCs.

grego wrote:
Here's a review on the lens and he talks about use with a TC, 1.4 and 2.
http://www.press-photos.com/html/review​s/sig120300.html?3

1.4 was said to be fine, but 2 is not worth it, unless you have one already.

According to this review, Canon extenders do work with it. I am going to get this lens soon, and apparently going to try my 2x tc out on it i guess.

Thanks for the link, this was exactly what I needed

condyk wrote:
In my experience there is no difference worth worrying about between HSM and USM on these long lenses. With the 20D you'll get better AF performance with 2.8 lenses too. If I was buying this lens I'd get a 1.4x and maybe look for a SH 2.0x to just try it, or borrow one if you can. I've never got good enough results with a 2.0x on these kind of long lenses. The Canon should work as they are essentially identical to the Sigma design. Check out pbase and photosig for shots ... you might be lucky tho' maybe a small user base of this combo

Thanks Condyk. I now know that the Canon 1.4 extender will work so I might as well get a second hand 2x t'con for those times it may come in handy.

Well if you are trying to pair a lens with a converter to one without, and they are both quality lens, the one without should win.

I have never done tests, but got images I was happy with out of the 70-200 IS with a 2x TC. However, I think i'd get similar results with a 2xtc in terms of image quality.

grego wrote:
Well there is nothing to compare........ There is no zoom like this one.

Only if we are looking at 300 vs 300, could we compare, and I'd take the 300 2.8L over the Sigma generally. But hey, I'm just a poor college student! And it's too hard to run off with a 300 2.8.

The very same reason I'm going for the Sigma

Thanks Cadwell. I'm primarily going to use the lens for wildlife so not quite the same need for ultra fast AF as you would need, but all the same it's good to know it's not far behind a lens like the 85 1.8

The 1.4 would get a lot of use so thats good news, as for the 2x it would only be used occasionally so I can live with that

The money I can save on the Sigma 1.4 as I already have the Canon will fund a second hand 2x.

672mm f4 will do for me.