Investigating Sensor Misalignment part 2
P. Fahrenfort, February 2009.
Continued from page 1.
Product shot
After I send the repair facility a link to the first page they took another look at the D300 and I just got it back. I first measured the deviation angle of the plane of focus with the beer cans a bit more accurately now and found about 12 degrees at a distance of 7.2 meters. So nothing changed. To investigate things at a closer distance, below a symetrical product type shot at about 3 meters. I focused on the two jars containing boullion using Contrast AF.
The NEFs are in the Project Directory, the images are all shot with D300 and 105VR @ f/2.8.
Then I clipped a piece from the the sides of each shot and put them in the image below. The photo where I focused on the left jar is on top, where I focused on the right jar is at the bottom. You can see that each clipping has a diferent sharpness distribution.
To show the full impact of the rotating plane of focus I put the two clippings from above that are most diferent side by side in the image below. Remember that this diference is invoked semi-randomly depending on focus distance and the placement of the focus sensor. In my opinion the difference is way too big and makes the camera professionally unusable. This type of shot needs accurate focusing and stopping down to get everything sharp enough without diffraction reducing the resolution.
Flat target
Now to find out why the techs still do not see the misalignment. If I shoot a 2 dimensional target at about 7.5 meters and focus in the middle, the difference between the left and right side of the image is not so large. This is because the left side of the flat target is just inside the backside of the depth of field, while the right side of the target is only just outside the front part of the depth of field. In the image below I focused in the middle and I show the left and right side.
But if I focus on the left bottom and compare that area with the area at the right top diagonally across the image I can cleary see too much unsharpness, despite the depth of field. The plane of focus is not only skewed horizontally but also vertically, so at the left bottom corner the plane of focus is closest to the camera and at the right top corner it's the furthest away.
Conclusion
The camera was performing fine before I brought it to the repair facility for a checkup. It seems the repair facility put their home made alignment in it that made the camera unusable to me, while they think it's fine and won't change it. It feels like I'm trapped, like in the Eagle song 'Hotel California': 'You can checkout any time you like, but you can never leave...'