Hello. I am not new to this forum in that I have been looking in for a long time. I learned a lot.
Below is a experience I would like to share and find out if others have experienced the same
I recently bought a RRS L-bracket for my a900. When using it with the sony 70-300 zoom I found vertical shots at 200 and 300mm to be seriously unsharp (1/30e shutter).
At first I thought there to be something wrong with the L-bracket (it is not extremely stiff in the vertical position). More experiments, on a heavy tripod with the legs short, showed that also when I used the camera in 90 degrees rotated head, the results where far from sharp. In a horizontal position the sharpness is excellent. I used mirror lock up for all tests.
When thinking about it, I realized that the shutter curtain moves vertical. This movement accelerates and stops directly in the direction of the center of the tripod. All vibration is in the vertical plain, in which the tripod is very stiff. In the vertical position the shutter movement tries to twist the camera sideways, in which direction both the L-bracket and the tripod offer less resistance.
I tried this theory by putting the camera on a nodal slide of RRS, in a horizontal position, as far as possible behind the center of the tripod. And yes, the results where not as poor as in the vertical position, but no longer critical sharp.
Could it be that this is a weakness of the a900? I never experienced this problem with the D2x I used before (that is less critical with its 12Mp, but still).
sorry if the post is a bit long.
Hans van Driest