Dpreview 测试 Z7 对焦不如 一般单反

我测试到AF－C AF－ON 锁上目标连续拍是可以对焦，，但是如果目标周围的有高反差物体，，Z７出现搞乱脱焦而转去高反差目标 （希望通过firmware可以改善）
目前单点对焦比较稳定

暗部对焦不是那么理想，，但是一但对焦，是很尖锐。 虽然其他nikon单反好象D810对焦成功率高，但是有很小的微跑焦。

看来Z7对于在夜间拍摄会很艰苦

https://www.dpreview.com/reviews/nikon-z7-first-impressions-review/5?utm_source=self-desktop&utm_medium=marquee&utm_campaign=traffic_source

还有这个鸟兄说那个 pin point focus 反差对焦（最小的）可以对焦比较准 （太小lar）


http://www.naturalart.ca/voice/blog.html#Z7_3weeks

7. Autofocus Performance

I am going to tackle this issue in a MUCH bigger way in a few months. It's not easy to figure out (or get reliable information about) how Nikon's Hybrid AF system (meaning "part phase-detect, part contrast-detect") actually works. As an example, it seems quite clear that the new "tiny" area mode called Pinpoint AF (available only when using Single Servo - or AF-S - mode) is fully contrast-detect. But how much of a role contrast-detect plays in the "other" AF-S modes and ALL the AF-C modes isn't clear. Many (including me) assumed that the "hybrid" AF system meant that contrast-detect was ALWAYS contributing to the AF (in any mode) and thus negated the need for any form of AF tuning on a lens. However, given that the camera allows the user to input AF tuning values for lenses makes me question that. And...I have read quotes of Nikon executives saying "Contrast-detect is always in effect when AF-S mode is used" but that assumes that the executive being interviewed actually knows what he/she is saying! Like I said, I will be digging into this fully in the coming months.

BUT...I CAN comment on several things about the AF system (based on my own use) already:

First, initial acquisition of focus on a subject seems very fast. When I pair my Z7 with a very fast focusing lens (like a 70-200mm f2.8E or my 400mm f2.8E) it snaps into focus extremely fast (so fast that it SEEMS as fast as my DSLR's, tho' this is a qualitative statement that I can't verify). I am more than slightly pleased (and pleasantly surprised) that the Z7 acquires initial focus as fast as it does.

Second, the predictive AF seems good, but NOT as good as on Nikon's best DSLR's. What's predictive AF? It's what your camera is doing when an object (like my dog, though he'll bite you if you call him an object) moves directly towards you (or away from you) and stays under the same focus point (the camera is actually calculating its exact position when the shutter exposes the sensor to light). So...when good old Poncho the Portie is running right at me I CAN get shots in focus (like this one of Poncho trotting at me and captured with the Z7 plus my 400mm f2.8E), but the hit rate (shots in tack sharp focus) doesn't appear as high as on my D5 (which is Nikon's best camera at this test). I say "doesn't appear" because I haven't had the chance to systematically test this so can't fully quantify it yet...but in time I will.

Third...on Focus Tracking: There's been a LOT of negative internet chatter about how Nikon has executed focus-tracking on the Z7 and on the fact that it doesn't have 3D-tracking (and I have also heard some complaints about how the Z7 doesn't have Group Area or as many Dynamic Area modes). As a wildlife photographer I almost NEVER use 3D-tracking for any form of action shooting - not with birds in flight, not with sparring grizzlies, not with any running mammals (or breaching humpback whales). While the 3D-tracking has improved a lot on recent DSLR's (its BEST execution is on the D5), in the brown-on-brown world of wildlife photography it isn't the "go-to" mode for MOST wildlife photographers when they are shooting action. Rather, they tend to use ONE of the Dynamic Area modes OR, if there's no chance of having foreground nab the wrong subject, Group Area AF. And, MOST wildlife photographers don't "bolt" their camera in one place and expect the AF system to track it all over their frame - rather, they PAN with the subject.

So...the Z7 DOES have 9-point Dynamic Area mode, and the area enclosed by the points is MUCH larger (i.e., a larger proportion of the frame) than on the D5. And...it works pretty darn well for panning on (and keep a moving subject) in focus. D5 good? Nope. But not too darned bad.

What about the missing Group Area AF modes? Well...they're not really missing - they've been re-named. On the Z7 there are two Wide Area modes where a MUCH bigger area than a single focus point acts as one BIG focus point (kinda like Group Area!). And, again kinda like Group Area, the AF system prioritizes on focusing on the closest object within the "box" that defines the focus area boundaries. And, the Wide Area S mode is smaller (compared to the size of the Group Area mode on a D850) and the Wide Area L mode is larger (again than the D850's Group Area AF). So...if you have to worry about keeping foreground out of the Wide Area bounding box you choose the S (small) option - if your subject is moving erratically choose the L (larger) option. Hmmm...just like Group Area, but with more size options!

Focus accuracy on the Z7? Seems very good in all modes...and incredibly good if you use the pinpoint mode, which is a very small focus point and is dedicated to contrast-detect AF. Where I have noticed the accuracy of that pinpoint mode the most has been when comparing the focus accuracy of wide angle zooms, like 24-70's (which always seemed a bit hit and miss with my D850 when I was focusing using the optical viewfinder).

Expect more to read more about the AF performance of the Z7 on this blog in the coming months...but at this point I can honestly say this: the AF system of the Z7 has exceeded my expectations. It most modes it is very fast, it's acceptable for panning, and - used correctly - it is deadly accurate.