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| p.1 #1 · Temperature causing softness? |
I just returned from a frustrating little excursion.
It was very cold outside (8 degrees F), and there was nothing I could do to get my long lens (500/4 IS) to take sharp photos.
It's a very sharp lens, and had shown that just last weekend (last time I was out with it; it was 30 degrees warmer then).
While contemplating the situation on the drive back, it occurred to me that, with telescopes, we have to give the equipment a long time to reach temperature equilibrium, or convection currents in the tube may hurt the image.
So, when I got back home, I let all the equipment reach equilibrium, and, voila, the lens was incredibly sharp, as I expect of it.
Is it a known problem with long (large volume) lenses that it takes them a while to reach thermal equilibrium, and that failure to allow that to happen runs the risk of ruining photos taken while out of equilibrium?