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Old September 28th 08, 06:11 AM posted to rec.photo.digital,rec.photo.digital.point+shoot
carlislestamford
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Posts: 8
Default Infrared photography

On 28 Sep 2008 03:51:18 GMT, wrote:

In rec.photo.digital DaveC wrote:

| I want to photograph and video in infrared mode.

I'd like to know the spectral range possibilities of various sensors, both
in how long they can go for IR, and how short they can go for UV (assuming
the filter on the sensor is removed or replaced). I have heard figures of
1000nm and 1200nm for IR, but no figures for UV.

Are there cameras with special sensors that go well beyond what normal cameras
intended for the visible spectrum can do?


When I was searching for IR-ready and UV-ready cameras (I had a penchant to
photograph all the hidden patterns in plants that insects and other animal
orders depend on) I found that the Sony "Super-HAD" CCD sensors had the most
sensitivity to the largest spectrum of IR frequencies, covering the widest
bandwidth with the most sensitivity (in consumer cameras). You can find the
spec-sheets on various CCD arrays online. This was (5?) years ago when I did my
initial research and I'm not about to recreate that for you by Googling it for
you again. The IR frequencies that you want to expose for on these sensors being
determined only by the bandpass filter used in front of the lens array. Their
"Super-HAD" CCDs are conveniently used in all their inexpensive "NightShot" and
"NightFraming" capable IR-ready consumer P&S cameras.

Now on the other hand, only one camera out there (no longer available, I don't
think, and I don't recall who manufactured it because it was prohibitively
expensive, I didn't even want to think about trying to purchase it) was designed
to do both IR and UV with the flick of a switch. It was an expensive specialty
camera manufactured by Canon, Panasonic, or some other popular company, designed
to sell to research and forensics investigation departments.

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.