Автор: Emoxide
Дата: 16-03-16 22:05
LENSES FOR CENTERING TESTING
If one tests. A lens on the imaging performance and function, so the first view of the centering should be directed Here manufacturing tolerances are most easily visible. The best optical calculation is useless if the smallest adjustment errors do everything again to naught. Many now test against a brick wall or bookcase and compare the corners, but the smallest error in the camera orientation falsify the result. Here is an easy and error-resistant test method will now be shown.
1) go to the door, looking for you a detached distant, well-structured object. There should be at least 20 meters, when tested with wide angle, it should be even more.
2) The camera comes on a tripod, mirror lock and cable release should be understood in telephoto lenses. At wide angle and short exposure time you can shoot even freehand.
3) The far removed object will be in focus with the center AF point and then the AF disabled. Right through the AF point in the example is running a power line in the foreground. This is not ideal but in this case, no matter because it is already in more than 400m and the AF does not offer much attack surface.
http://www.gletscherbruch.de/foto/test/dezentrierung/mitte.jpg
4) If the lens is acceptable sharp even at maximum aperture, the further test is taken at maximum aperture. If the sharpness in the corners only dimmed good, so the test is performed dimmed one or two stops. Off-centering sees also dimmed and a certain sharpness the picture must have been to compare the corners can.
5) Best is the exposure and aperture now set in the manual mode, because for the next 4 pictures they must remain constant.
6) The targeted object is now included with all 4 corners. So you can directly compare the corners together, as object, aperture, distance and focal position has not changed.
http://www.gletscherbruch.de/foto/test/dezentrierung/ecken.jpg
7) On the picture above you can see now quite clear that the lens is decentered. The left side is less sharp than the right side.
This strength of decentralization is still viewed at Canon as normal Fertigungstolleranz. It is normal images not particularly striking, this test is very accurate. Who does however many mosaics, will think twice if he is to retain as an objective or not, for an adjustment is rarely possible and only under great effort. Show all tested lenses a weakness on one side, so it is probably not the objective, but at an angle built-in image sensor. In the case of the flange back of the camera must be recalibrated and adjusted.
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