Canon 500 F4 vs. Sigma 300-800 F5.6

I love my Canon 100-400 but find that it often doesn't have enough reach for some wildlife shots. I can't decide whether to go with a Canon 500 F4 IS with 1.4x tc or a Sigma 300-800 F5.6 for the really long shots. IS is not much of a factor in my purchase decision since the lens will alway be mounted on a gitzo with wimberly head. I know the Canon can deliver high quality photos with my 20D but the few shots that I've seen from the Sigma were impressive and it is less expensive. I'd Like to get recommendations/sugges​tions from anyone that has experience with either of these 2 lenses, especially the Sigma.

thanks

qUICK REPLY ... THE verY BEST SHOTS i HAVE SEEN ONLINE WHERE WITH THE sIGMA 300-800 AND Sigma 800 PRIME LENSES. aWESOME ... AND (ooops, sorry for CAPS!) they have an awesome price tag attached too

http://www.suesbirdpho​tos.co.uk/ for examples of the Sigma's.

However, after much research, as usual with me, I have just ordered the 2 latest Kenko extenders from HK, the Teleplus Pro 300 2.0X DG and the Teleplus Pro 300 1.4X DG, with the long term idea to use with the Canon 400mm L. The user reviews have been superb, at least as good as the Canon and Sigma variations. They are much cheaper too!

I thought I'd get both and check if the 2x degrades the image, as is sometimes reported with the Canon and Sigma options. User reports seem to say not, but I got the 1.4x just in case. I will sell one or the other once I've checked.

They're much cheaper than the Canon and Sigma options and have Hoya glass, so sound very promising. Might just be worth checking to see if ther Kenko 2x could really pull up your 100-400 to the length and quality you want. You can then spend all that cash on erm .... and new house, or something

I've only seen one.. never used one (the Sigma) and it is physically simply the largest lens you can mount on a Canon body with the exception of the esoteric 1200mm. So consider that as well,. as the 500mm L will seem compact in comparison!

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Someone posted a link to samples from that lens just recently on this forum

A torontonian bought it with a 20% discount on christmas sale at henrys.

Let's see if I can find it.

Thanks Condyk - the bird photos are awesome. I've used the Canon 1.4x tc with my 100-400 but found the resulting images to be a bit soft. Other than its size and weight (13 lbs), the Sigma appears to be the best solution for distant subjects. However. I'd like to see what a 400 prime with a 1.4/2x tc can do.

I use the sigma 50-500 with a 2X tc and it produce great pictures

Here's a link to some pictures from a birder who just got his Sigma 300-800 EX DG
http://forums.dpreview​.com …orum=1029&threa​d=13014003

I have just purchased sigma 300-800 and borrowed a gitzo tripod with wimberley head ...Am hoping that aprrox 60 % of my shots of fast moving aircraft are only blured because i am getting used to the lens. Have a feeling that I will need to use higher shutter speeds to stop this however this will freeze the props ! has anyone else had similar problems ? and maybe a solution ? Running canon eos 1d mk2.