Tus lej ua ntej lub iav tsom iav qhia qhov kev nthuav dav, piv txwv li, 8X30 qhia tias qhov loj ntawm lub iav yog 8x.
Yog tias nws yog hom ob-tus nqi, cais ob tus lej nrog / cim. Piv txwv li, 2x / 4x txhais tau hais tias qhov kev nthuav dav ntawm lub iav tsom iav yog 2x, thiab muaj thaj tsam ntawm lub iav tsom iav nrog qhov loj ntawm 4x. Yog tias lub lens yog duab plaub, qhov dav ntawm lub lens yog qhia los ntawm tus lej dhau los, thiab qhov siab ntawm lub lens los ntawm tus lej hauv qab no yog qhia hauv millimeters. Piv txwv li, 100X50 txhais tau hais tias qhov dav ntawm lub lens yog 100 hli thiab qhov siab yog 50 hli. Zoo li telescopes, shoddy magnifiers kuj nyiam ua ib qho fuss txog magnification, thiab nominal magnification feem ntau ntau dua qhov tseeb magnification. Qhov tseeb, qhov kev nthuav dav ntawm ib lub lens magnifying iav yog tsawg dua 10 npaug, thiab qhov sib txawv ntawm ob lub lens magnifying iav yog tsawg dua 20 zaug. Yog tias qhov xav tau kev nthuav dav yog siab, yuav tsum muaj lub tshuab tsom iav. Cov sijhawm sib txawv yuav tsum tau siv qhov sib txawv ntawm qhov sib txawv, tsis yog qhov siab dua qhov kev nthuav dav, qhov zoo dua, qhov kev nthuav dav siab txhais tau hais tias qhov kev pom yog me me, qee zaus qhov kev pom yog qhov tseem ceeb dua. (Magnifier=250 / Lens focal length ntxiv rau 1, mm units)