For those of you that have tried both the D5 and D4s, how will you describe the difference in AF- performance?
Low light and tracking (BIF/football/sport)?
I don't have experience with the D4s, but have used other cameras of the same generation (D810, D750) and the D5/D850. The most pronounced improvements made by the D5 AF system (Multi-CAM 20k module, additional processor etc.) compared to Multi-CAM 3500 series AF systems is that using reasonably fast lenses (see manual for details) there is a large coverage of cross-type AF sensor points, including the outermost columns in addition to the center columns in the older system. This makes a huge difference when photographing e.g. a person in full body size (with the face focused on) approaching towards the camera. Basically the outermost columns act with almost perfect reliability now, whereas with the older system those sensors were linear and sometimes would not pick subject detail. I do a lot of this type of photography in vertical orientation, both in portraiture as well as sports photography, and it has been a big change.
Other improvements include:
* AF sensitivity in low light improved
* Each AF point covers a smaller part of the frame, so there is less cross-talk from surrounding areas (if you use single point mode)
* Sophisticated multi-point modes that are fast and useful, including
- 9-, 25-point dynamic area which are without front/back bias, effective in focusing on subject position that is not the closest part of the subject
- group-area which is closest-subject priority within the designated area, effective in focusing on distant subjects against complex backgrounds, also effective in low light
- I could also mention auto-area-AF and 3D Tracking which work well now but typically I prefer the more controlled approach of the previously mentioned, more confined modes (D9, D25, group, and single point); these modes existed before but the speed of the D5 makes them much more effective and reliable than in the past.
I generally photograph people with AF and tend to use wide apertures a lot. With the D5, in-focus percentages tend to be around 90-100% depending on conditions, in extreme low light at night the percentages in focus do fall somewhat, but are still much higher than with cameras utilizing Multi-CAM 3500 series AF modules (with the D810, I would get 30-70% in focus at wide apertures, the lower figure is in low light indoor situations and the upper figure in typical outdoor daylight photography). This is with f/1.4 or f/2 lenses; with some of the best focusing f/2.8 or f/4 lenses (e.g. 70-200/2.8G II or E FL) things tend to be better for both cameras, and the difference is evident in low light where the D5 continues to be reliable in darker lighting conditions than the D810.
One area where the D5 does particularly well is when photographing subjects where the fur or hair is lit by the sun from behind; the D810 would easily pick focus on the hair instead of the face or eyes, because the hair was still within the larger focus point (they sensitivity areas are bigger than shown in the viewfinder) and focus on the brighter lit hair. The D5 doesn't do that, using single point or 9-point dynamic the focus is solidly kept on the face (in fact it is easy to keep it on the eyes and avoid the nose, by keeping the D9 area on the eye and cheeck below the eye, avoiding the nose). Also, another area of excellence is approaching subjects, which tend to be more difficult for earlier cameras.
My subjects (for AF) tend to be events (both daylight and nighttime), some sports (figure skating, running). I was exhilarated the first time I shot with the D5, it was a midsummer celebration outdoors and I was just amazed at how the D5 could focus on dancers with almost perfect results until things got fairly dim (ISO 25600, f/2.8, 1/500s was when I got the first hunting using the 70-200/2.8G II and D5; after that focusing was still possible but required a bit more care). The best focus performers out of my lens set have been the 24-70/2.8 E VR, 70-200/2.8 G II and E VR.
I know I don't have any data on the D4s, but I hope this is still helpful.
