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Automobiles with internal combustion engines need a ‘running in’ period when new. Manufacturers advise against heavy acceleration or continuous work at high load or high revolutions in the first 1000 kilometers or so. This is to allow machined components moving in contact with each other to wear slightly allowing them to settle in and operate smoothly.
I have recently tested several lenses which when new showed evidence of decentering indicated by obvious unsharpness on one side of the image in a focal length range. After repeated use, the unsharpness disappeared.
The lenses in question were the 16x zoom in one of my family’s Panasonic FZ1000 cameras, a PanaLeica 15mm f1.7 M43 lens and a Panasonic Lumix 12-35mm f2.8 M43 lens.
As part of my usual routine I tested each of these lenses when it arrived in my household. I do this by making a series of general photos out and about at various focal lengths (in the case of the zooms) and apertures.
Then I take the lenses inside and photograph my standard test chart with the usual protocols: tripod, OIS off, E-Shutter, timer delay, AF and MF for comparison. The camera was carefully centered on the test chart as usual.
With each of these lenses there was obvious loss of resolution on the right side of the frame, in one focal length range (in the case of the zooms).
I wondered if one or some of the zoom or focus elements in the lenses might be moving slightly out of position as the lens operated.
In the old days the glass elements of a lens were mounted in a brass mount with a helical thread. To focus, the mount was rotated thereby moving the glass element(s) back and forth.
This system is way too slow for modern contrast detect AF systems which drive the focussing elements directly back and forth on little rails. I imagine the manufacturing tolerances involved must be extremely fine.
I also imagine that if there is a slight irregularity in the surfaces which slide against each other, it might be possible to rectify this by a process analogous to ‘running in’ an internal combustion engine.
So, I put each lens through a series of exercises.
With the zooms I zoomed wide, then focussed at the closest possible distance then at infinity, 50 times. Then I zoomed out to the longest focal length and repeated the focus-close, focus-infinity cycle 50 times. I repeated all this at intermediate focal lengths.
In the case of the FZ1000 I increased the number of near-far focus cycles at each focal length to 500. This was pure guesswork, I had no idea if the strategy would work or how many zoom/focus cycles might be required.
Results
It worked.
Each of the lenses is now performing perfectly, with no sign of decentering or unsharpness.
Suggestion: If your new lens appears not to be performing to specification try giving it a workout.
You might get a pleasant surprise.
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