Old 04-04-2021, 06:23 PM
MarkInSpace (Mark)
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Telescope thermal sensitivity (for focusing)

Is there a difference in thermal sensitivity for different telescope designs?
I have a refractor and I need to constantly refocus if the temperature changes.
Do some telescope designs have more thermal resilience?
eg Cats vs Refractors vs Newts vs RCs etc...
Maybe the only answer is to get carbon fibre tubes?
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Old 04-04-2021, 09:04 PM
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The_bluester (Paul)
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Many refractors are relatively stable. The focus point on my SVX80T moves, but not a large amount. The SCT on the other hand changes focus lots, and quickly. On a cool night after a hot day it can go from pinpoints to doughnuts in 20 minutes.
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Old 05-04-2021, 07:45 AM
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multiweb (Marc)
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The smaller your CFZ the more issues with temperature and focus drift. Insulating the tube helps a lot. With dew as well.
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Old 05-04-2021, 07:53 AM
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Aluminium tubes are best for APOs because the change of focus of the lens with temp changes is partially matched by the contraction of the alum tube.
Carbon fibre then is not recommended for APOs per AP's Roland Christen also because of thermal currents it can cause.

Carbon fibre on the RC and CDK I have works super well but then the issue is more the temp difference between ambient and mirror temps.

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