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Cool down time for a 120mm f5 refactor

Equipment Refractor
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28 replies to this topic

#26 vtornado

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Posted 24 November 2022 - 01:58 PM

I don't have your scope, but I do have a 120 ED doublet f7.5 doublet, metal lens cell.

 

I have not done a formal test of course, but I do notice some softness of view

when I take the scope out from 68F house to 30F outside.   100x works well,

I notice the softness when exceeding that.  Sometimes I go back inside, or

I switch to another low power target.  It seems about 30 mintues before the

scope is sharp at 150 to 200x.  Nights of 200x seeing are extreemly rare.


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#27 lxeth

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Posted 24 November 2022 - 04:53 PM

When you first go out and set up for your observing session, is there any benefit to setting up a refractor so that it points straight down, without the diagonal installed, so that the inside of the tube is open with the focuser at the top?  This would seem to be a good way to allow the warm air inside the tube to rise and go out the focuser, and let the inside surface of the objective lens contact the outside air, and thereby cool down faster.  But, does doing so cause other problems?

That's an interesting idea! I never thought of it...the only problem that I can think of (in my limited experience) would be dust getting into the tube, but if you put a thin towel or something like that over the focuser tube, then that should limit that...makes sense...I'll have to try and see!



#28 Oldfracguy

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Posted 24 November 2022 - 06:28 PM

I use a piece of left over window screen over the front of my 8" Newtonian when that is cooling down.  I set the 8" Newt at an angle just to take this picture, but it's vertical with the screen on top during the cooling process, with the fan on the back running.

 

101_1846.JPG

 

I actually came across an article where someone does actually recommend placing a refractor objective down, and leaving the diagonal out of the focuser to let the warm air inside the tube escape.  It makes sense from a heat transfer perspective, but are there any downfalls or negatives to this approach?


Edited by Oldfracguy, 24 November 2022 - 06:30 PM.


#29 CQDDEMGY

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Posted 24 November 2022 - 08:48 PM

This is a low power scope. There is no cool down.


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