Steve said:
jrista said:
A native 5.6 is a bit more successful, although still limited (line points only, no cross types). At f/6.3, it's a tossup whether your body will AF successfully with it or not. Something like the 5D III/1D X are going to have more luck than a 7D or 70D, the latter may not lock at all, and if they do, they are not guaranteed to actually have the best focus.
True "sports" lenses have native apertures of f/4 or faster, and maybe f/5.6 with a TC (i.e. the 200-400).
Yeah, I don't know. You're comparing your experience with a 2x TC at f8 with native apertures. My 300 2.8 with 2x TC is slower focusing than my 300-800 5.6 even though they are the same effective aperture. I don't have a Tammy but I've not seen anyone who's reviewed it saying that it has difficulty focusing on any camera body or that it limits the number of focus points. I mean apart from the FUD types who think any non-Canon/Nikon lens is worthless garbage, that is. Ideally, yeah, you'd want to shoot sports with the largest aperture possible but a lot of newspaper types shoot with 70-300 non-L variable aperture lenses and get printable shots.
I spent some good time with the EF 300 f/2.8 L II (I rented it twice...once on StackExchange's dime, as I won a contest, and once myself). I used it at 300/2.8, 420/4, and 600/5.6. On my 7D and on a rented 5D III. Even on the 7D, that puppy locked focus fast enough to get a lock on a BIF at 600/5.6. It wasn't particularly fast, and the lock was sometimes not solid (the bird might not actually be fully in focus at first, then clean up a few frames in...that was one of the 7D's long-standing problems). On the 5D III, focus lock was not really an issue at 600/5.6, but again, not super fast. It was wicked fast at 420 and 300...absolutely no issues, and tracking is extremely precise...precise and consistent to a degree I've never seen at f/5.6 on any lens. That's the key difference...the added capabilities of Canon's AF points at f/4 and f/2.8. At f/5.6, you lose those extra capabilities, which give you increased accuracy and precision.
I'm curious what 300 f/2.8 you were using. The original, or the Mark II? Or even a different brand? (Different brands are a different story...they don't necessarily communicate right with the camera, so you might get different results...for example, my Kenko 1.4x TC lies to the camera, makes it think it's faster than it is...the camera tries to focus faster...but it's precision and accuracy drop.) The Mark II superteles have advanced AF firmware. That firmware works well with the 7D, but exceptionally well with the 5D III. Roger from LensRentals has some good articles on how and why and what the differences are.
I'm not against third party lenses. I believe there are certain risks you take when you use them, and they are usually not compatible with Canon's full SDK, but they can be definite money savers, and they can often get the job don well. That's beside the point, though. You don't generally call an f/6.3 lens a "Sport" lens. Sports professionals look for f/4 and faster because it's not just the AF unit and firmware in the camera that gets the job done. At least in Canon systems, the lenses also have AF firmware, and the two work in concert to determine what capabilities of the AF points can be utilized, and faster lenses can be significantly faster, more precise/accurate, and more consistent in how and where and when they focus or track than lenses that are f/5.6 and slower. You also gain the ability to use more focus points, and more of them as cross type or double cross type, at faster apertures.
That's something reviewers often seem to either ignore, or they simply don't know about. I've seen reviewers using f/5.6 lenses, then complain about the 1D X AF system's performance. Well duh!
Of course it isn't going to perform as well, your using single-line AF points. To really fully and properly test out the 61pt AF system, you need to use fast glass. The differences are quite significant, and its at those apertures that Canon's whole system REALLY shines.
