Question about CCD and IR

Hi,
We all know that CCD element can detect IR, my question is, could it
also used in thermal-imaging, since it is IR sensitive?
Thanks

Haider Albassam

wrote:

Hi,
We all know that CCD element can detect IR, my question is, could it
also used in thermal-imaging, since it is IR sensitive?
Thanks

Haider Albassam



The longest-wavelength silicon CCDs (based on high-resistivity silicon,
which allows carriers to be collected from the full thickness of the
chip) crap out at about 1 um on a good day. The band gap of silicon is
about 1.2 eV, so nothing longer than that will be detected directly.
People have put electron-storage materials (basically europium salts
with a few magic ingredients) on top of CCDs, which allows detection out
to maybe 1.4 um. Past that, all options become very very expensive.

Thermal imagers designed for scenes near room temperature are generally
sensitive in the 8-14 um band, about 10 times longer than the cutoff of
silicon.

The cheapest commercial thermal IR cameras are the 16x16 arrays made by
Irisys, at about $1000. I made some 100-pixel ones for a project at
work that cost about $10 for the complete sensor and optical system, and
about $100 more for the back end. You can read about them at
http://www.pergamos.net, but (alas) you can't buy them yet.

Cheers,

Phil Hobbs

On 18 Feb 2005 03:34:11 -0800, wrote:

We all know that CCD element can detect IR, my question is, could it
also used in thermal-imaging, since it is IR sensitive?

That depends just what you mean by "thermal", but basically, no. The
sensitivity of silicon sensors drops to essentially zero above 1.1
microns. That corresponds to a blackbody temperature of about 2600K. So
you can barely image things that are fairly hot (I've seen soldering
iron tips on CCDs). But you can't detect something like a person
radiating body heat.

_________________________________________________

Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

wrote:

We all know that CCD element can detect IR, my question is, could it
also used in thermal-imaging, since it is IR sensitive?

I defer to more knowledgeable posters for this topic, but do have a somewhat
interesting sidebar to offer:

A few years ago, IR sensitivity in consumer imaging devices presented a
major "Oops" for some manufactures, in the form of unanticipated (blush)
nastiness. The uh, "artistically inclined" (AKA: pervs)... were eager to get
the early non-modified versions and/or ordered altered cameras:

http://www.kaya-optics.com/products/voyuerism.shtml

Many consumer oriented digital imaging devices now employ "modesty
filtering", usually consisting of an IR attenuating cover glass/filter over
the array.

But some digital SLRs (with specialized uses in mind) are now modified or
designed without the filter (Canon 20Da to be available soon), while
dedicated astro-CCDs have always been sans-modesty filters. Hey... maybe I
should plonk a lens onto my SBIG STL11K and bring it to the beach! )

Cheers,

Paul (suffering cabin fever while patiently awaiting an AP160 and a second
SM90 solar H-a filter to do the 0.5ang double-stack thing... WooHoo!)

PS: Now if only SBIG would replace the cover glass on my camera's array,
perhaps my Newton's Rings problems would go away:

http://www.astro-nut.com/sun-ha-newtons-rings.html

--- http://www.astro-nut.com ---

Paul Hyndman wrote in part:

A few years ago, IR sensitivity in consumer imaging devices presented a
major "Oops" for some manufactures, in the form of unanticipated (blush)
nastiness. The uh, "artistically inclined" (AKA: pervs)... were eager to get
the early non-modified versions and/or ordered altered cameras:

Widespread ill-informed remarks such as that caused Sony's lawyers to
cripple Sony's otherwise excellent-for-ir DSC F-717 and 828 cameras.
They were "dialated" in firmware so that daylight IR photography with
full manual shutter and exposure control was made more diffcult without
and IR pass filter *plus* lots of additional attenuation.

http://www.kaya-optics.com/products/voyuerism.shtml

Well, let's face it: the above link is run by pretty sleazy people.
Can't say for certain whether or not the images have been exaggerated,
but the mpeg link sample is probably illegal for other reasons. Also,
note that the pages touting "see-through" capability are usually trying
to sell you soooper-secret spy gear, and are shaky on the science.
Before you whip out the broad brush, let's get a little perspective:

http://infrareddreams.com/how_to_shoot_ir.htm
http://www.kenrockwell.com/tech/ir.htm
http://dpfwiw.com/ir.htm


Many consumer oriented digital imaging devices now employ "modesty
filtering", usually consisting of an IR attenuating cover glass/filter over
the array.


Meanwhile digital IR still occurs, thanks to clever modifications and
inginuity on the part of them there "pervs."

Pervs such as:
http://www.lostcanuck.com/galleries/Infrared/index.html
http://leppinstitute.com/awards/IPA/ipa2005.htm

And last and maybe least,
http://www.unclaimedmysteries.net/di...s.php#infrared

But some digital SLRs (with specialized uses in mind) are now modified or
designed without the filter (Canon 20Da to be available soon), while
dedicated astro-CCDs have always been sans-modesty filters.

Great, now astrophotographers can get slimed with the same false "perv"
reputation!

Hey... maybe I
should plonk a lens onto my SBIG STL11K and bring it to the beach! )


Knock yourself out, flapjack. Sorry if I got a little chippy here but
I've grown tired of having to be put on the defensive over something
that people should be better informed about.

--
It Came From C. L. Smith's Unclaimed Mysteries.
http://www.unclaimedmysteries.net