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Phil,
once you've used the ground glass/FM-60 combo to focus the camera....( withouth the film loaded ) you probably wont have to refocus again for your nights photo session....any temp swings are not going to affect the focus enough to worry about it.........UNLESS you are using LONG FOCAL LENGTH scopes........(2000 mm focal length and up )
I have shot pentax 6 x 7 using a/p 155 f 7 and Tak FSQ 106 mm f-5 and never changed focus during a session of shooting.........and never have noticed difference in focus on the stars........ MAYBE if you used a magnafying loop on the negative you might notice some SLIGHT differences...........but on 6 x 7 format ,,,,,,,,,,,,,printing a 4 x 6 print the enlargement isnt very much......this no critical visual differences in focused star appearances
Broose K
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