Helen B
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Ed,
I don't think that anybody would argue with you that special glasses are not required for lenses designed for UV imaging, or that UV attenuating glass can only be a coated product (UV filters are available that are made of unlaminated, uncoated glass). This thread is, however, about glass for framing, and the UV-filtering glass-based glazing that is sold for that purpose has the UV filter either coated (eg Tru Vue Museum) or laminated (eg the reassuringly expensive Schott Amiran TN - which has a PVB interlayer - this also provides protection from shards as a side effect), to the best of my knowledge. Anti-reflective coatings also tend to reduce the UV transmission, both for camera lenses and for glazing (this effect can be seen in the Tru Vue UV blocking figures).
Perhaps to save you digging up the Zeiss UV lens info, here is what Cox has to say in Applied Photographic Optics: "...optical glass in general has little transmission below about 350 nm, and when high refractive index glass using lanthanum is used, transmission is restricted to beyond 400 nm, especially if anti-reflection coatings are used. Likewise, optical cements can have specific high UV absorption. Others are available which transmit down to 220-260 nm. Careful choice of glasses can give a lens with a useful transmission above 380 nm; the principal use is in enlarging on to UV sensitive materials, thus reducing exposure time.
...
A true UV lens must be made of other optical materials such as synthetic fuzed quartz or silica, which are not birefringent, and synthetic fluorite, all of which transmit freely in the UV. ... Optical polymers have poor UV transmission."
He later points out that elements cannot be cemented together in a true UV lens, and that cement has a supplemental role as a UV filter in lenses intended for visible light photography.
As you say, the refractive index of ALON is indeed higher than quartz (about 1.8 vs 1.5 in the VNUV.
Oh, Cox has diagrams of the Zeiss UV Sonnar 105 mm (215-700 nm, quartz and fluorite); UV Micro Nikkor 105 mm (220-900 nm, quartz and fluorite); Zeiss UV Planar 60 mm (320-450 nm, quartz and glass); and Rodenstock UV Rodagon 60 mm (glass, intended for enlarging onto UV sensitive materials).
Best,
Helen
I don't think that anybody would argue with you that special glasses are not required for lenses designed for UV imaging, or that UV attenuating glass can only be a coated product (UV filters are available that are made of unlaminated, uncoated glass). This thread is, however, about glass for framing, and the UV-filtering glass-based glazing that is sold for that purpose has the UV filter either coated (eg Tru Vue Museum) or laminated (eg the reassuringly expensive Schott Amiran TN - which has a PVB interlayer - this also provides protection from shards as a side effect), to the best of my knowledge. Anti-reflective coatings also tend to reduce the UV transmission, both for camera lenses and for glazing (this effect can be seen in the Tru Vue UV blocking figures).
Perhaps to save you digging up the Zeiss UV lens info, here is what Cox has to say in Applied Photographic Optics: "...optical glass in general has little transmission below about 350 nm, and when high refractive index glass using lanthanum is used, transmission is restricted to beyond 400 nm, especially if anti-reflection coatings are used. Likewise, optical cements can have specific high UV absorption. Others are available which transmit down to 220-260 nm. Careful choice of glasses can give a lens with a useful transmission above 380 nm; the principal use is in enlarging on to UV sensitive materials, thus reducing exposure time.
...
A true UV lens must be made of other optical materials such as synthetic fuzed quartz or silica, which are not birefringent, and synthetic fluorite, all of which transmit freely in the UV. ... Optical polymers have poor UV transmission."
He later points out that elements cannot be cemented together in a true UV lens, and that cement has a supplemental role as a UV filter in lenses intended for visible light photography.
As you say, the refractive index of ALON is indeed higher than quartz (about 1.8 vs 1.5 in the VNUV.
Oh, Cox has diagrams of the Zeiss UV Sonnar 105 mm (215-700 nm, quartz and fluorite); UV Micro Nikkor 105 mm (220-900 nm, quartz and fluorite); Zeiss UV Planar 60 mm (320-450 nm, quartz and glass); and Rodenstock UV Rodagon 60 mm (glass, intended for enlarging onto UV sensitive materials).
Best,
Helen
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