如何选择放大镜.doc

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1、HowtoChooseaMagnifierSELECTINGTHERIGHTMAGNIFIERFORYOURPURPOSESTochoosethecorrectmagnifierforthejob,firstdeterminewhattoolsaretobeusedonthejob;thendeterminethesizeandthecharacterofthesubject;andfinally,analyzetheobject'ssurfacecharacter.Thenreviewthefollowingaspectsofmagnifiers:NumberofElements:Asin

2、glelensissatisfactoryforlowpowers.Higherpowermagnifiersrequiretwoormorelenselementsforimprovedresolutionandcorrectionofchromaticorotheraberrations.WorkingDistance:Thedistancefromthemagnifiertotheobjectviewedistheworkingdistance.Thisdistanceisanimportantconsiderationwithregardtothetypeofworkthatmust

3、bedoneunderthemagnifier.Ifyourworkrequirestheuseoftools,amagnifierwithalongworkingdistancewillallowenoughspacetobothusethetoolsandcomfortablyviewtheobject.Smallworkingdistancemagnifierswithhigherpowersarepreferredforclose-upinspectionwork.FieldofView:Thefieldofviewistheareaseenthroughthemagnifier.A

4、spowerincreases,lensdiameterandfieldofviewdecrease.At5power(5X),fieldofviewisabout1.5".At10power(10X),itisabout0.5".Usually,itisbesttouselowpowerforscanninglargersurfacesandhighpowerforsmallareas.EyeRelief:Themaximumdistancetheeyecanbefromthemagnifierandstillprovideafullfieldofview.Longereyereliefs

5、generallyprovidemorecomfortableviewing.DepthofField:Thedistancebetweentheclosestandfurthestpointsatwhichamagnifierinafixedpositionstaysinfocus.Thedepthoffielddecreasesaspowerincreases.Coating:Lenssurfacescoatedwithspecialanti-reflectioncoatingswillreducelightlossandareparticularlyusefulforlow-level

6、lightapplications.Magnification:10"isassumedtobetheclosestdistancethehumaneyecanfocusforcomfortablevision.Anobjectonly1"fromyoureyewouldbe10timeslarger,butoutoffocus.Amagnifier'sfunctionistoassistyoureyeinfocusingcloser.Sincea1"focallengthlensbringsclearvisiondownto1"fromtheeye,anobjectatthisdistan

7、ceisclearlyseenandappearstobe10timescloserthanitdoeswhenviewedfrom10"away.Suchamagnifieriscommonlycalleda10Xor10power.Usingthisdefinition,themagnifyingpowerofalenscanbeapproximatedasfollows:MP=10/FLifthefoc