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Old September 28th 08, 08:48 AM posted to rec.photo.digital,rec.photo.digital.point+shoot
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Default Infrared photography

In rec.photo.digital carlislestamford wrote:

| UV is a whole other beast to contend with. Most optical glass in nearly all
| camera lenses is a good absorption filter for many UV wavelengths. Even the
| micro-lens array and Bayer-filter on the sensor is a UV blocking filter to some
| extent. Imaging most of the UV bandwidths requires special and EXPENSIVE lenses
| that will allow transmission of UV to any electronic sensor. Short-wave UV
| transmission is totally obliterated by nothing more than a layer of flint or
| crown-glass as thin as the material in a drinking-glass or standard
| daylight-filter. In high-resolution UV photomicroscopy, for example, it requires
| specialty lens elements made of hard pure-quartz and soft fluorite, throughout
| the whole light-path, from subject to recording medium. Due to the high melting
| point of pure quartz and the difficulty in figuring soft (and easily
| moisture-destroyed) fluorite into the right curves (the reason L-Glass lenses
| are so expensive) you aren't going to easily obtain camera lenses that can
| transmit a wide bandwidth of UV with most consumer's bank-accounts. Most CCD
| cameras will be somewhat sensitive to the long-wave UV spectrum, but only some
| of it. Limited by the very optics that are a part of all white-light-imaging
| lens assemblies. Long-wave UV, yes, you can reach into that bandwidth somewhat
| successfully with standard lenses and common CCD sensors, but don't even think
| about imaging in the short-wave UV spectrum with any of the standard glass lens
| elements available on the market. Even L-Glass lenses are incapable for this use
| because they are a mixture of more-common glasses elements plus fluorite
| elements. The standard flint and crown glass components (as archaic examples
| only, there are hundreds, if not thousands of modern glass recipes) will quickly
| filter-out any short-wave UV that the L-Glass lenses' few fluorite elements
| might pass.

What about plastic lenses we ordinarily would scoff at? There are some better
quality plastic materials these days. Maybe it could be a semi-useful, even
if not the best quality, lens specific for shorter UV that you could ever hope
to get out of glass, without having to mess with quartz.

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