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Variations in focusing summer and winter
I was out on Thursday night trying to image NGC6121 with my DSLR on live view and noticed straight away that I had to wind the focus out quarter to half a turn from the bottom in order to achieve good focus on the stars. Whereas during the warmer months I usually image various DSO’s ( 3 to 6 magnitude objects ) with the focuser wound right in as far as it can go for good focus.
I’m assuming the reason for this is the colder air temperatures ( of late between 8deg to 14deg ) contracting the metal of the focuser ,optical tube and brackets etc.. which may
change the focal length in the telescope
Is this a reasonable explanation of the change in focus ?
Appreciate any advice on the observation
Thanks in advance
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