· Get a Cloudy Nights T-Shirt · Submit a Review / Article    Click here if you are having trouble logging into the forums Cloudy Nights - Official Forums of the 2009 International Year of Astronomy Privacy Policy | Please read our Terms of Service | Signup and Troubleshooting FAQ | Problems? PM a Red or a Green Gu.... uh, User   You are not logged in. [Login] Forum Archives · Entrance · Main Index · Search · New user · Who's Online FAQ · Calendar Equipment Discussions >> Binoculars Previous   Index   Next   Threaded   Pages: 1 EdZ Professor EdZ Reged: 02/15/02 Posts: 14731 Loc: Cumberland, R I , USA42N71.4W temperature affect on focus       #3434260 - 11/07/09 08:22 AM Edit   Reply   Quote Quick Reply   I've noticed this before, and it came to light again last night. I was observing last night intermittently from about 7pm to about 1am. During the course of that time, temperature dropped from the mid-upper 40s to the mid 20s. And I suppose when I first set the binoculars up at about 6:30-7pm, they were still at about 65° room temperature. So throughout the course of the evening, the binoculars dropped from 65° to the mid 20s, a 40 degree temperature change. Two or three times during the night I had to refocus the Garrett 22x85. Something that is never necessary during the warm months. So, worthwhile to keep in mind, it pays to get your gear outside to acclimate. Not so much of an issue with small gear, but for big gear it is an issue. Temperature changes do have an affect on all that mass, especially when the focal length is about a half meter long. edz -------------------- Teach a kid something today. The feeling you'll get is one of life's greatest rewards. member#21 Post Extras:       Erik D Post Laureate Reged: 04/28/03 Posts: 3196 Loc: Central New Jersey, USA Re: temperature affect on focus [Re: EdZ]       #3434308 - 11/07/09 09:12 AM Edit   Reply   Quote Quick Reply   The GO SS 22X85 is of aluminium construction, close to 16 inch(~406 mm) in length. 40 deg F delta = 22.2 deg C. Coefficient of linear thermal expansion for Al is ~23/1,000,000 per deg C A 40 F/22.2 C temp drop would result in ~ O.2 mm contraction of binocular housing. Dimensional displacement of the objective spacing, prisms and eye pieces are additional factors to consider. Coefficient linear thermal expansion for steel is approximate 1/2 of aluminium. ERik D Post Extras:       Pages: 1 Previous   Index   Next   Threaded   Extra information 10 registered and 11 anonymous users are browsing this forum. Moderator:  EdZ  Print Thread Forum Permissions       You cannot start new topics       You cannot reply to topics       HTML is disabled       UBBCode is enabled Thread views: 77 Jump to *International Year of Astronomy 2009* -----   Global Coordination   Cornerstone Projects   Special Projects   Special Task Groups   Global Activities   National and Regional Activities   IYA 2009 in Africa   IYA 2009 in the USA*Announcements and News* -----   Cloudy Nights Announcements   Discussion of CN Articles, Reviews, and Reports   Beginners Forum   Celestial Events   Light Pollution*Equipment Discussions* -----   ATM, Optics and DIY Forum   Binoculars   Binoviewers   Cats & Casses   Classic Telescopes   Equipment   Eyepieces   Mounts   Observatories   Reflectors   Refractors    Celestron SkyScout and Meade mySky   Video and Electronically Assisted Astronomy*Astrophotography and Sketching* -----   Beginning and Intermediate Imaging   Film Astrophotography   DSLR & Digital Camera Astro Imaging & Processing   CCD Imaging & Processing   Solar System Imaging & Processing   Sketching   Astro Imaging/Sketching Contest *Observing* -----   NEO   General Observing   Planetary and Solar System Observing   Lunar Observing   Deep Sky Observing   Double Star Observing   Solar   Variable Star Observing and Radio Astronomy*Telescope Specific Forums* -----   Celestron NexStar    NexStar GPS / CPC Telescopes   Questar Forum   Meade ACF/RCX / LX / GPS    Meade ETX*Other* -----   Science of Astronomy & Space Exploration   AstroWebsites   Space Rocks*Speciality Forums* -----   AstroArt   Astronomy Software & Computers   Stellar Media   Astro Outreach, Clubs and Star Parties*CN Feedback and Vendor Announcements* -----   Vendor and Group Announcements CN Forums Home

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