Caution: I am not a repair technician. This is just what I did on my own D300 body.
First, there are two hex screws inside the mirror box on the left side (right side as you're look face-on at the camera). The one closest to the mounting ring adjusts the focus of the AF-focused image on the viewfinder's screen. It provides the mirror's stop position. The second, and more important screw is behind the main mirror, and adjusts the stop for the AF system mirror. This is the main one you'll want to adjust if you're having a focus issue.
Use a fixed focal length lens. Use a fixed focal length lens. Use a GOOD fixed focal length lens. If you don't have one (which is known to be properly calibrated) go and rent one. I had months of trial-and-error using my reasonably-expensive Sigma 70-200mm f2.8 lens until I realized that it was subject to about a 1.5" focusing error at 6 feet (minimum focusing distance for that lens). Using my 50mm f1.4 was a cinch, and I ended up finally nailing the focus in just a few minutes time with it. Once you have it set at a small, but sharp f-stop (I used f2.0 on my f1.4 lens, it still has very narrow depth of field), check it with all of your lenses (and teleconverters).
The hex screws work on eccentric-shaped pins. Moving the hex wrench up moves the pin back, moving the hex wrench down moves the pin forward. There is a VERY small range of adjustment needed to move the focus point quite a bit. For the front hex head, up on the stop pin moves the focused image closer to your eyeball. Down on the stop pin moves it farther from your eyeball. It is a reflected image off the mirror, after all. Attention: Do not adjust this until AFTER the camera is taking sharp photos, confirmed on your monitor. For the rear hex head, down on the pin moves the focus FARTHER from the camera, while up moves it CLOSER to the camera. In this case you are moving the image forward and back on the focus sensors mounted in the floor of the mirror box. Hopefully your lens is doing its best to resolve the image properly at the sensor plane.
If you find you're taking big swings at it, something is wrong with your lens (as I figured out somewhat late). Any focusing error up close will be grossly magnified when shooting in the distance. If you optimize your AF system witha front-focusing lens, shooting at infinity will be impossible (it will all be blurry).
On the bright side, if you've gotten to the point where you want to try this and you simply cannot send your camera to Nikon for 3 weeks, give this a shot. It's fairly difficult to massively screw up your camera beyond the point it already is, and if you do, there's always Nikon Service to fix it.
BTW-I used both the "Sensor Cleaning Mode" to adjust the screws and occasionally simply lifted the mirror carefully with my finger and used the allen key on it. Be prepared to have to dust off your sensor if you use the "Sensor cleaning mode" as all sorts of dust will land on it while the shutter is open.
Good luck!
Thursday, August 26, 2010
Wednesday, August 25, 2010
More Nikon Autofocus thoughts
First, never attempt to reset your focusing with a zoom lens. My 70-200mm f2.8 Sigma has a close-focusing error at minimal focus distance, and this was causing me to screw up my attempt to reset my AF system on my D300. I was zooming in on something close (to better see where the area of sharp focus was). Once I went to the Nikon 50mm f1.4 body, things went much smoother. Now I'm getting pretty much laser-like images, all the way down to wide open settings, so I'm much happier.
Second, using single-point AF in the dark sucks on the D300. Cars in the darm (on a lit track) must not offer as much contrast for a single point to grab onto. Eventually I went to the 9-point grouped sensor setting and began to get sharp photos. It's very frustrating switching through the modes and getting shot after blurry shot. The 51-point "3D mode" simply does not work well for cars. There's too much area covered by the points, and it often grabs focus on a point outside the area the car occupies, resulting in out-of-focus photos. At a track, where there's often a white wall visible in the dark, the Nikon AF will CONSISTENTLY find that white wall in 51-point mode. Grrrrrrrrr. 9-point AF works well. I'd love to see Nikon add a 15-point mode, where it adds 3 more sensors to the left and right of the 9-point square, for a more horizontal configuration friendlier to cars. I don't need the additional 6 vertical points of the much slower-to-focus 21-point mode. Pretty please, Nikon? Can I have this in the next software update? I'm sure no one is reading this blog.
Third, though my 50mm f1.4 is the sharpest lens I own by far, its incredibly-slow focusing system will NOT capture cars in real-time. I discovered this in Long Beach in April, at the Formula Drift event, and rediscovered it in Las Vegas last weekend. My cheap 18-55mm Nikon "kit" lens is faster (though not by much). As a result I wound up using my much heavier Sigma 70-200mm f2.8 lens through the night. Boy did this make my arms tired!
That's all for now!
Second, using single-point AF in the dark sucks on the D300. Cars in the darm (on a lit track) must not offer as much contrast for a single point to grab onto. Eventually I went to the 9-point grouped sensor setting and began to get sharp photos. It's very frustrating switching through the modes and getting shot after blurry shot. The 51-point "3D mode" simply does not work well for cars. There's too much area covered by the points, and it often grabs focus on a point outside the area the car occupies, resulting in out-of-focus photos. At a track, where there's often a white wall visible in the dark, the Nikon AF will CONSISTENTLY find that white wall in 51-point mode. Grrrrrrrrr. 9-point AF works well. I'd love to see Nikon add a 15-point mode, where it adds 3 more sensors to the left and right of the 9-point square, for a more horizontal configuration friendlier to cars. I don't need the additional 6 vertical points of the much slower-to-focus 21-point mode. Pretty please, Nikon? Can I have this in the next software update? I'm sure no one is reading this blog.
Third, though my 50mm f1.4 is the sharpest lens I own by far, its incredibly-slow focusing system will NOT capture cars in real-time. I discovered this in Long Beach in April, at the Formula Drift event, and rediscovered it in Las Vegas last weekend. My cheap 18-55mm Nikon "kit" lens is faster (though not by much). As a result I wound up using my much heavier Sigma 70-200mm f2.8 lens through the night. Boy did this make my arms tired!
That's all for now!
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