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Old 20-07-2006, 01:40 PM
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RB (Andrew)

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Join Date: Aug 2005
Posts: 21,908
Originally Posted by Jonathan
Hi Roger. One reason for this is that ED (Canon call it UD I think) glass changes size slightly with temperature so the position of infinty on the focus ring can change depending on the temperature. Only 1 of my lenses stops at infintity and it's a non-ED glass lens, the rest go past infinity, the longer the focal length the further past it goes.
Hence the need to check focus throughout the night if your imaging all night.
It's not a basic set and forget.
As temp changes so does focus.

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