Quote:
Originally Posted by ZeroID
MMmm, interesting. Looks like I will be taking the wee muffin fan off the back of the Serrurier and saving a bit of weight.
What about dew control ? I have an even smaller fan directed at the secondary from one side. Not sure how effective it is but as it's spread would be far greater than the secondary area I would expect very little possibility of uneven thermal movement.
Yeah, I know we're splitting hairs here but it's an interesting discussion. I think I'll be removing both fans now anyway.
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Having fans blowing ACROSS the front face of the primary mirror removes the image disruption of a thermal layer/boundary forming in the air column directly above your mirror (forms due to the temperature differential between the warm mirror and cooler ambient air temperature and causes heat shimmers in the optical path). Whilst this fan(s) will have minimal cooling benefit it will definitely improve your seeing and optical performance. You should accordingly move your primary cooling fan just forward and perpendicular to the primary mirror.
There may be a similar optical improvement regarding your secondary mirror fan, depending on the direction of airflow in relation to the secondary light cone. If it's not introducing either vibration or unequal thermal equalising of your secondary or adding undesirable weight to the top end of your OTA it's probably not hurting you.