When the D800 was released, there was a lot of debate as to the usefulness of a sensor with that much resolution, one’s ability to hand hold and still get sharp frames, and the size of the files it produced. These are all valid points, and all important considerations when working with a camera of this resolution – particularly a DSLR camera because of its adaptability and speed. One thing that I did not see too much concern about, but have recently become acutely aware of, was the AF sensor.
In a Nikon autofocus SLR camera, light enters through the lens, passes through a semi-transparent mirror, bounces off the autofocus mirror assembly, and hits an autofocus sensor behind the mirror. All of this happens in nearly real time and tells the lens motors how to focus the lens. A genius of a system when it works well. Not so much when it doesn’t.
Last weekend I was out on a personal guerrilla style shoot with my good friends Andy Faulk and Elle Carly. We took a break from shooting to grab a coffee and soak up the sun a little, and I took the opportunity to take a look at a few of my frames. To my (at the time unexpressed) horror, only two or three frames about of about 100 were in acceptable focus.
At first I shrugged it off as narrow depth of field, and/or that third cup of coffee, as I had stared the day with some frames at f/1.4 and a few cups of that certain caffeinated beverage. But as I flipped through, even those at f/8 and f/11 were missing critical focus. What was I to do? I couldn’t call off the shoot on these two lovely folks because my camera wasn’t cooperating. So, I kept shooting, and I kept getting the same results for the rest of the day.
When I got home, I resolved to take the D800 and my lenses into the Nikon service centre and have my lenses aligned to the body – figuring that this was the problem. A couple of new Nikkor G-type lenses, a couple of AF-D lenses, a Sigma 35mm f/1.4. I figured they probably wouldn’t all be aligned perfectly.
I was wrong. All my lenses were spot on. The AF sensor and mirror assembly in my D800 had moved slightly with use. We’re talking microns here. The tiniest little movement in that sensor had caused my photos to be out of focus most every frame. This is not uncommon in cameras that are used frequently, according to the service centre. However, it is nowhere near as noticeable on lower resolution sensors so most people never have to realign their AF sensors, they said.
So there we have it, probably the most potent problem with the extremely high resolution sensor in the D800. Camera shake can be rectified with a tripod, hard drives can be bought, and resolution can be downsized when it isn’t needed, but keep an eye out for that AF sensor. That one will ruin every single frame you shoot.
Below are a couple of quick frames from the shoot. These ones are sharp enough to be useful, but the final image shows a detail crop of my focus area. Bare in mind that this was shot at f/8 on and 85mm f/1.4. That should be just about as sharp and contrasty as is technically possible, but it is far from that.