I used the Canon 400mm f/5.6 for a long time until I discovered what the Sigma 150-500mm could do. I've heard the Sigma 50-500mm is even sharper. I've moved on to the Sigma 300-800mm and Sigma 120-300mm f/2.8 but you should consider the 500mm zooms from Sigma at this price point. IS is unimportant if you shoot with a tripod or use a shutter speed of 1/focal length of the lens or faster. I have IS on the 120-300mm but I turn it off.
I'm not sure where you heard that, but the (low-end) Sigma zooms are not even remotely close to the 400 5.6 - here's the 400 compared to the 150-500 compared @400mm, wide open:
The Canon is sharp from center to corners with just a hair of CA, while the Sigma is blurry mush with CA from mid-frame to the corners.
The Sigma 120-300 is a huge step up from the 150-500, but at 420mm with the Sigma 1.4x it's still not as sharp as the 400 5.6, even stopped down to 5.6:
The 120-300 is a fine lens, but if you want a sharp lens at 400mm, you can't beat the 400 5.6. The only lenses that are sharper at the focal length are the 300 2.8 IS II + 1.4x III ($7,299) or the 400 2.8 IS II ($10,999). Even the 200 2 IS + 2x III and 400 DO aren't as sharp.
The 400 5.6 is by far the best 400mm for the money and gives professional results.
Thank you Mackguyver for ruining my day! Haha!
I have the Sigma 150-500mm and knew it was a mushy mess already, especially when I picked up a Canon 70-300L last year, wow what a difference. But I hadn't seen that direct comparison between the Sigma and the Canon 400 before. Holy S___ that is horrible!
I was already going to sell the Sigma and pick up the Canon 400, but damn, I can't sell that thing fast enough! I think some of my family may be getting smaller Xmas presents this year so I can afford that sexy little 400, I love how small it is too!