Multi-CAM 20k AF system behavior (D5/D500)

[MFloyd]

I bought Steve Perry's book. Thank you for the recommendation 😊

[chambeshi]

Here's a recent official article by Nikon on the D5 AF modes for different sports

http://nps.nikonimaging.com/technical_solutions/d5_tips/af/recommended_af_settings/description/

Found it in the latest contribution to this thread, which seems to have exhausted the topic (!)

There's a large thread going on at http://www.fredmiranda.com/forum/topic/1478115 about the difference in behaviour of the D5/D500 AF and the older Nikon's

[Frank Fremerey]

Thanks for the link! It is quite a long discussion. I guess Nikon designed the dynamic area AF to be emphasize more the selected point than the surrounding area compared to how dynamic area AF worked in cameras based on around the various Multi-CAM 3500 series modules.  This hasn't really worked for me as my motivation to use a larger AF area than single point is because I may not be able to hold the single AF point precisely on the target and need the camera to retain my main subject in focus even when this happens and decidedly not focus on the background if I slip as the current D5 dynamic area AF seems to be doing frequently. To be honest that's the problem I had with dynamic area AF on D7100 and D810 as well, the camera is so eager to focus on the main point I kind of feel it defeats the point of using a larger area. Perhaps the backgrounds that I have are too detailed, so the focus is easily slipped there. Nikon does recommend the use of group area AF if the subject is hard to follow using a single AF point and to reduce the risk of the camera focusing on the background, which is exactly my problem with the dynamic area AF modes. Group area AF does work well for me but in horizontal orientation it cannot be off-centered on the top part of the frame as much as I would like, so in practice group area AF is more useful for me on vertical compositions than horizontal. It works especially well for relatively distant subjects where the subject is fully within the depth of field (so the exact point choice within the subject isn't critical) but background is relatively close and could potentially attract the camera's AF system.  As the subject approaches Nikon seems to think  it is best to switch to dynamic area AF ("You can then press a focus function button to select group-area AF when your subject is far away and release the button as the runners approach to instantly switch to 25-point dynamic-area AF without taking your eye from the viewfinder. "). I suppose I should give this approach a try.

Stopping down a bit does help in the situation where group area AF has focused on the torso of the subject and the face in the upper part of the body is closer, but I find I prefer the look of wide open shots most of the time for the "pop" of the subject from the backgrounds. For shooting at f/2.8 or f/2 precise control of the focus point is key. Vertical compositions don't have this problem now that cross type points extend close to the edges of the frame in that direction but for placing multiple athletes in a horizontal composition and selecting the face of just one of them can be difficult using FX. I don't mind having to crop a bit from the top to solve the issue but this does lead to the use of a single point to avoid having to crop too much. Anyway, if I use f/4 then I'm usually quite happy with group area on the chest unless the subject comes really close in which case no amount of depth of field will quite solve the issue. (Well, f/8 might but then the ISO will be quite high in many winter sports lighting scenarios).

one of the reasons I chose the D500 is that I wanted to have at least one body with AF point coverage of next to the whole frame

[Ilkka Nissilä]

I've been testing 3D tracking on people on the street (May day celebration) and once the operator understands what it is doing, it works shockingly well as long as there is no obstruction in the line of sight between the subject and the camera. If the subject is temporarily occluded, the camera tends to lose the subject and continue on something else in the immediate surroundings. Restarting tracking after the subject is again visible is virtually instantaneous on the D5 and 70-200/2.8E. I think for this type of subject matter the resulting focus accuracy is actually better than I can do with manual control of focus point. This is because the system uses all 153 focus points and is able to compensate for small lateral subject position changes better than I can. However it cannot handle blocked view of the subject or a pirouette in figure skating so for that, auto area AF works better. Auto area AF isn't quite as precise as 3D tracking when the conditions for successful tracking are in place though.

I've had the camera for almost a year now and I keep finding features of value that I had not thought to use because they didn't impress in previous generations. Tagging a subject and tracking it with recomposing and zooming as the situation evolves is something quite amazing. What remains for the photographer is to know the limitations of each feature. E.g with FX one needs to be aware of what the camera is likely to do when the subject's face leaves the AF sensor array, for example, and how to predict moments where there is likely a discontinuity in tracking and how to recover from it (it is easy). And when not to use 3D tracking.

What is interesting is that Nikon chose to show the active point as one of the 51 manually selectable points instead of showing the in-between points when they are being used. The result is that sometimes the point that is shown as active is outside of the subject but the subject is still precisely in focus. The reason is that an in-between point was selected by 3D tracking but the camera or viewnx-i show only the nearest point in the 51 instead of one of 153. I think probably the correct point is stored in the exif but for some reason it is not shown. Maybe a future firmware upgrade and software update will show it.