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| Author | Subject: prisms and varifocals |
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 tsagal
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prisms and varifocals
Dec 05, 2006 17:12:05 Can you incorporate a prism into varifocals - if so how? - worked only? Can you have different prisms for near and distant in the varifocal? many thanks |
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sbharuchi
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RE: prisms and varifocals
Dec 07, 2006 18:46:04 I think it is worked only. i dont think you can have different prisms for dv and nv in varifocals. i would have thought that you would prescribe the minimum amount of prism that eliminates both. if that doesnt work then i suppose you could move on to sperate pairs for dv and nv or bifocals with worked worked prism in dv area and fresnel stick on for near....or franklin split bifocals. Correct me if im wrong!!exam in december too. |
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Stephen Meynell
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RE: prisms and varifocals
Dec 07, 2006 19:19:34 Yep - you got it right. Vari's have vertical prisms incorporated to thin them down .Both sides have base up prisms for the thinnng anyway. You can ask for a prism to be worked into the vari - but its accross the whole of the lens. You measure the prism by putting the fitting circle central on the focimeter. I think Franklin splits are obsolete - but you can get bonded segments with prism incorporated. =hope it helps - steve |