Getting the correct focus in any camera can be trying at times. There is nothing worse than coming home and discovering your photograph is not sharp due to a focus error.
The Nikon Multi-CAM 3500 module installed in the D800 is the same as in the D4 and D4s. Is has a total of 51 auto-focus points covering a decent percentage of the viewfinder. There is not as much coverage as I would like. But until Nikon comes out with an improved focus sensor, we Nikon shooters are stuck with this.
In the smaller format sensor cameras, like the D300s, D7100, and the like, this sensor coverage area is quite good. A significant portion of the entire viewfinder is covered. But in the larger, full-frame sensor viewfinders like on the D800, the coverage is not as good.
What about those sensors? In the middle three columns, the critical cross-point sensors are jammed together. These are the useful and sensitive points that lock onto just about anything and really hold on. Even in low-light conditions, these focus points do a pretty good job.
However, the rest of the points are vertically oriented, so they only detect horizontal contrast lines. This means that if any of the above vertical focus points are placed over an object with dominantly vertical lines, they will not be able to focus at all.
Don’t believe me? Try it and you’ll see. Find a hard edge vertical line, say a white piece of paper on a black card. Set the camera to single point focus, single-AF mode. With the vertical focus point hovering over a vertical line, you will discover that the camera will not lock onto that focus point.
If you start to tilt the camera so the vertical line starts to appear diagonal over the vertical focus point, you will find an angle at which the camera is able to lock onto the now diagonal line. Keep this angle in mind. If you try to focus on something in those outer points that is more vertical than your test angle, just know that your camera, your $3000 to $6500 camera, will not focus on it.
It’s a frustrating part of this technology. Although Nikon says that most of their test shooters focus in that middle area, I find I routinely have to do the focus and recompose maneuver to keep a good lock on a subject. So many times my subject focus area is not anywhere near that cluster of 15 focus points.
Whether you are a Nikon, Canon, or other manufacturer shooter, knowing the types of focus points in your camera will help you understand why your camera does really well or totally falls apart when trying to focus on an object.