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Thread: Refractor cool down times..?

  1. #1
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    Default Refractor cool down times..?



    This morning I was up at the crack of 4:15. Thank you, Mr. Bladder. I took a peek out the back door and was treated to a very clear sky. Knowing that Ganymede was going around the back of Jupiter, I thought it might be worthwhile to stay up. I keep a 102SLT (OTA on a pipe mount) for a quick grab 'n' go at the door. At only f/6.5, it's not the best on planets, though. I put it outside, and went to get my orange C80 (f/11.3 ).
    I would have gotten my dob, but since it was -19C (1F) out, I knew the Sun would be up before it cooled
    Brought the 80 out, and since ten minutes had passed, I thought I would take a look through the 102. It should be cooled down, as supposedly 'fracs are way faster at that than dobs. Uh-huh. Tried to focus, no go. Hmmm. Went inside for 10 minutes (coffee), and thought, OK, 4:35, should be good. Been outside for 20 mins. Go back out, a little better, but still no sharp focus. Tried the 80. It was like trying to use my dob after 5 minutes in this cold.
    By the time the 102 was good to go, it was ten to five. Nice view, but a little too much CA for me on Jupiter. Over to the 80, and it was still a bit fuzzy. It was 5:10 before it settled into its usual self.

    So all that to say, it took the 102mm 25 minutes to cool, and the 80mm 45 minutes.

    Is this normal? I've had both out at 10C (50F) and in 5 minutes, they're good to go. I guess 45-50 degrees F might make a difference. I'm wondering if it's the volume or displacement of the air inside the tubes; perhaps that's why the 102, even though larger in diameter, took less time to cool that my long 80mm.

    Anyways, just my observations. I've only owned any type of refractor since last summer, so this was new to me. In hindsight, I should've brought out the dob... Still, the view was great through the 80; saw all four moons (including Ganymede, slipping in behind the gas ), and a pinkish dot which I knew was the GRS. So I'm happy. And tired
    More coffee!


    All the best,

    Mark
    Last edited by TheFatKitty; 01-08-2017 at 07:13 PM. Reason: Tired...:)
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  2. #2
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    Default Re: Refractor cool down times..?

    I'll say the larger the temperature differential, the longer the cool down time.

    I set mine out yesterday about 1600 hrs., so I had about a 3 hour window for acclimatization. No issues for me (expect for Ol' Hateful).

    Granted, your's was impromptu, and with the looming dawn, not much time to wait it out.

    Maybe, if you anticipate a good sky with the next Cracking Bladder, set the scope out the evening before?
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    Bryan
    Scopes: Apertura AD12, RACI/Telrad; ES AR127, RACI/Rigel QF, Twilight II; Orion ST80, Twilight I; iOptron MC90 Mak, Cube-G Mount; Meade Telestar NG60
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  3. #3
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    Default Re: Refractor cool down times..?

    Re: So all that to say, it took the 102mm 25 minutes to cool, and the 80mm 45 minutes.

    Hello Mark,

    the difference in the cooldown times looks to me like some possible fogging on your 80mm, which might have sublimated away in 45 minutes.
    What helps on the refractors is to make a lens hood over the lens cell with some heat isolating material. This slows down the heat transfer and protects the lenses from fogging.
    Try it, if it helps, when not, then take into account longer cooldown times.

    Best,

    JG
    Binoculars: Leica Ultravid 7x42; Swarovski EL 8.5x42 Swarovision; Carl Zeiss Jena 7x50W and 10x50W; BA8: 10.5x70, 15x85; 25x100FB Refractors: Sky-Watcher 150mm/750mm; Leica APO Televid 82mm (25x-50x WW asph); EPs:Baader Classic Orthos; Leica WW; Tele Vue; Swarovski SW; Pentax XW; ZEISS W & Zeiss diascope B WW T*; UWAN; Filters: Astrodon, Astronomik, Baader (CCD), TS; Astrophotography: AstroTrac; Leica cameras R7, R8: Leica 2.8/100mm and 3.4/180mm APO lenses; Zeiss Sonnar 4/300 on Nikon F70;
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    Default Re: Refractor cool down times..?

    A lot of things will determine cool down times. Temperature differential, thickness of tube/ glass. Usually the diagonal will take longer to cool than the scope will.
    I will usually set my diagonals out 15-20 minutes before taking the scopes out
    Scopes: Antares Elite (Vixen Spec) 105mm f/15 (AIM-9), Modified SLT 102mm f/6.5 (Abe Normal), 2 Modified 150mm f/8 doublet (Frankencannon & Beefractor), Stellarvue NHNG DLX 80mm f/6.9, Vixen ED 115S f/7.7 (Raquel), Home made 150mm f/5 Newt
    Mounts: Manfrotto 055 Pro/ 128RC, Modified SLT, EQ-2, EQ-5, Tuned CG-5 w/ Argo Navis, Tuned ASGT, SXP w/ SB10 Binoculars: Vixen Ascot 10x50, Celestron Skymaster 15x70

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  7. #5
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    Default Re: Refractor cool down times..?

    Quote Originally Posted by Gabby76 View Post
    A lot of things will determine cool down times. Temperature differential, thickness of tube/ glass. Usually the diagonal will take longer to cool than the scope will.
    I will usually set my diagonals out 15-20 minutes before taking the scopes out
    Did not know that about diagonals. Interesting. And thanks for that tip.
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    Bryan
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    Eyepieces: GSO Superview 30mm; ES 70° 25mm; ES 82º Series; GSO 9mm Plössl; Zhumell Z Series 5mm; Vite Aspherics 23mm, 10mm, 4mm; Orion Expanse 20mm, 9mm
    Binoculars: Pentax PCF WP II 10x50, Bresser Corvette 10x50, Bresser Hunter 16x50 and 8x40, Garrett Gemini 12x60 LW, Gordon 10x50
    Observing: Herschel Tallies: H1 = 400/400 H2 = 252/400 H3 = 149/300; 2,349 observations of 1,438 objects; Led Zeppelin


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    Default Re: Refractor cool down times..?

    I give all my scopes with the diagonals at least an hour sometimes 2. The eyepieces I am now keeping in my hoodie pocket nice and warm. Trying to let them acclimate as well has not worked this year for me.
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  9. #7
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    Default Re: Refractor cool down times..?

    Thanks Gabby,

    I agree with the cooldown problems on the diagonal, as the quartz diagonal has quite a mass, and so its metal housing. It's a sort of wrong design for the cold environments, if compared with a high-end spotting scope protection of the prism, as designed for the temperatures down to -20°C, or even lower.
    Best,

    JG
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    Default Re: Refractor cool down times..?

    Interesting I do not have these problems at the moment but when I move back to Europe it will be, thanks for all the tips so if one leaves the diagonals out do you put then in a plastic bag or just open ? was wondering if dew gets in
    Richard
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    Default Re: Refractor cool down times..?

    Hello Richard,

    myself, I don't take the diagonal out, otherwise I would risk some humidity getting into the OTA.
    My scope is kept at a lower humidity environment (below 40%) than the regularly higher humidity outside.
    The scope is also kept in a not heated room, so the cooldown outside is fast and so much a problem.
    It may become a bit different, should your equipment be kept on display next to the fireplace, ha, ha.

    With my spotting scope, there is no problem at all.

    Best,

    JG
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