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Old 17th September 2013, 06:55 PM
neilL neilL is offline
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Join Date: Mar 2010
Member of: NOFTC CRPC
Location: Oxford
Posts: 576

I think it was back last winter when I did a simple experiment. I placed two rifle+scope rigs on a bench outside with a digital thermometer taped to the scope box to display the temp drop, with ambient temps in the sub-zero. I focussed at high mag on a branch at the back of the garden (with the 50ft lens the wheel was in the tricky 50-55 yd range). Then as the temp dropped I checked the focus without touching anything. The image was always near as dammit in focus but when I gave the sidewheel a big movement (end stop to end stop) and re-focussed the wheel indicator was 'shifted'. So for the scopes I tested (Nikko and Leups) the optics don't shift but the mechanism does end up with an offset as Rob described. As others find once the temp drops below some value the shift stops. Slightly more puzzling, I sometimes find there is a residual offset when it all warms back up above the shift temp. Which bugs me no end :-)

Have fun!

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