Nikon AF Problem
First off, this is with a D7000 and 70-200 VRI, mainly near the 200mm end.
Ive noticed that my last few sets have a lot of missed focus. Consistantly about 3 feet behind the focal point in the veiw finder. Image is always crisp and clear in the view finder, but on review theyre throw aways. What confuses me is, not all of my pictures have the same problem. Some still turn out just fine. The conditions have been lighter subjects (people and young fawns to be exact) against dark green foliage, on overcast early evenings.
My first thought was not enough ambient light, but focus didnt hunt one bit and my AF typicaly still works in much darker conditions. Contrast is pretty high between the subjects and the background too.
I tested this by locking focus a few feet ahead of the subject and recomposing. Perfect images every time.
Should I use the AF calibration in the camera to correct this, or should I try something different?
Ive noticed that my last few sets have a lot of missed focus. Consistantly about 3 feet behind the focal point in the veiw finder. Image is always crisp and clear in the view finder, but on review theyre throw aways. What confuses me is, not all of my pictures have the same problem. Some still turn out just fine. The conditions have been lighter subjects (people and young fawns to be exact) against dark green foliage, on overcast early evenings.
My first thought was not enough ambient light, but focus didnt hunt one bit and my AF typicaly still works in much darker conditions. Contrast is pretty high between the subjects and the background too.
I tested this by locking focus a few feet ahead of the subject and recomposing. Perfect images every time.
Should I use the AF calibration in the camera to correct this, or should I try something different?
D7000/D5000 | Nikkor Glass | SB600's | RF602's | CS5/LR3
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Fine tuning does vary by zoom and distance, so you get a quadruple whammy in the 70-200. My copy (also VR1) on a D4 for example, needs AF=-3 at 200mm at middle ranges, and -20 near infinity. The good news is that it's falloff is very slow, so the actual resolving power at -3 at infinity is only down about 10%, so I can pick a happy medium. My suggestion is that to understand the problem better, fine tune against targets at your typical shooting distance, which means you can't use tools like lens align or a diagonal ruler very well, you need to shoot against the whole scale of adjustment (say in 10's first) and look at the pattern to pick the range, then further refine it. Use AF-S, single point not any tracking or auto, on a tripod, shoot several images at each distance (defocusing each time), with a delay if the D7000 will do it.
Then if you are a bit compulsive as I am, do it again at shorter distances and see how much it varies; then at 70 vs. 200; then pick a compromise.
If you find it was off, then do more shooting in real life to see if you are happier. Bear in mind real life is all that counts - focus charts and controlled tests are not the end result.
If your camera supports it, you might look at Reikan Focal. Here. I have no relation other than as a customer. It's a bit pricey but I found it worth it to get more consistent results (and if buying it you should consider the pro as if you like the product you will eventually want it). It's not well documented but you can test against ad hoc targets like a distant telephone pole with it.
I forgot to mention, I did switch from AF-A and auto tracking to AF-S with a manual focus point when I first noticed the problem. It didnt clear anything up, or help the problem.
If you have the aperture wide open, do not use focus and recompose. Try to find a focus dot close to the area of desired prime focus and use that instead. Focus and recompose will generally result in back focus.
http://digital-photography-school.com/the-problem-with-the-focus-recompose-method
http://www.visual-vacations.com/Photography/focus-recompose_sucks.htm
In really low light, when only the center focus dot finds and locks focus quickly, you may also use a loose composition with the center AF dot, and then recompose through cropping the image in post processing.
Moderator of the Cameras and Accessories forums
Right. I describe the AF dots as "nebulous"* in nature.
*neb·u·lous/ˈnebyələs/
Adjective:
In the form of a cloud or haze; hazy.
(of an idea) Unclear, vague, or ill-defined.
Moderator of the Cameras and Accessories forums
Thanks for the tips!
What confuses me is, I haven't had this problem until recently. Could dirty contact between the lens and body cause this? I don't have any reason to believe they're dirty, but I also have not cleaned them.