MalVeauX wrote in post #17181591
It depends on what you're shooting and what you want to do with the image at the end of the day (print or not). To me, not crazy. But then again, I went with the Tamron for the 600mm. Because I only basically shoot it at 600mm. Why else get that length right? I too shoot wildlife with that lens pretty much exclusively.
The Canon 400 is going to focus a little faster, so if you combine the new 7D2 with the Canon 400, you get higher ISO performance and the robust autofocus of the 7D2, and the speed of focus from the 400. That means you can do more action wildlife, like the beginnings of birds in flight. But, reach limited. I find you still have to be pretty close to get decent frame fillers. Otherwise, you're always heavy cropping even at 400mm on APS-C. So if you want to focus on action, the 400 is probably worth keeping.
The 600 is optically as good, frankly in my book. But that's just my experience. 600mm F8 on the Tamron is a staple for me. People forget it's a $1k lens, not a $6k lens. They try to say it's bad, but they're not putting it in context. It's 600mm that is quite decently for only $1k. But it doesn't focus as fast. It's fast, but it's not lightning like the Canon whites can be. That extra 200mm does make a difference though. Significantly. So if you do a lot of wildlife that isn't super fast (like not shooting King Fishers in flight), then you probably will enjoy the 600mm with its VC more. More pixels on target. The nice ISO performance on the 7D2 will just help you keep shutter speeds high, which is very useful at 600mm + APS-C factor. I try to keep my shutter over 1/1000s frankly when I shoot mine. Even for still wildlife.
So two tools for two jobs.
I shoot my 600 on APS-C for most wildlife. I keep a 200 F2.8 on my other APS-C for the action wildlife at closer range.
Optical quality aside, these were off the hip as I was trying to get the images before some stupid tourists were walking up on the bird, here's 400mm vs 600mm in terms of real world difference in terms of pixels on target, from the same location, probably 80~100 feet away from this blue heron:IMAGE LINK: https://flic.kr/p/nUm59S IMG_6338
, on FlickrIMAGE LINK: https://flic.kr/p/obLzx9 IMG_6343
, on Flickr
This is still not a frame filler, even at 600mm and APS-C. Still takes a lot of reach to fill a frame. So I totally know what you mean by never having enough reach.
I use my 600mm with a 2.0x TC sometimes (live view focuses fine). For 1200mm. This is what I do with that:IMAGE LINK: https://flic.kr/p/padBgm IMG_0666
, on Flickr
Obviously not as optically good with the TC, pretty soft. But my point is the reach in terms of figuring out if you want more reach or not. 1200mm lets you really get close from far away. It costs you though.
I just don't have the budget for $3k~6k lenses. So this is from the point of view of being ok with a lesser lens, in the $1k ballpark.
I find cropping a 400mm shot is not as good as a straight up 600mm shot, as pixels on target matter. This is why I ended up on the Tamron, and didn't stay with the Canon 400's. But I also do not really shoot "action" wildlife.
Food for thought.