Doc,

Thanks. I am also an Electrical Engineer (Carnegie Mellon
University - 1969, 1970, and 1974) who has worked in electro-optics, radar
and optical communications for my entire career. While I have always been
interested in amateur astronomy, my interest has greatly intensified in
the last two years. It is a very challenging, technical hobby. The MAPUG
posts, your web pages, the pages of others on collimation, home
observatories and all of the advice so willingly offered by MAPUG members
has been invaluable. I owe a lot to all of you.

Best regards,

Bill Keicher



At 11:05 PM 4/23/2004 -0500, you wrote:
>Wonderful post, Bill. I used to know most of this back when I was studying
>Electrical Engineering as a graduate student. But that is 50 years ago.
>Thanks for the reminder and total clarification of these issues.
>
>Doc G
>
>----- Original Message -----
>Sent: Friday, April 23, 2004 10:27 PM
>Subject: Re: [M]: 201XT Problems...Dual Brightness Readings?
>
>
> > The infrared (below red) portion of the spectrum begins at
> > wavelengths longer than 700 nm (red) and extends out to the submillimeter
> > region. By convention, there are near infrared, mid-infrared and long
>wave
> > infrared bands that correspond to the atmospheric "windows" from 700 nm to
> > ~ 2000 nm, 3500 nm to ~5000 nm and 8000 nm to ~12000 nm. Others have
> > defined these bands differently. Technical people who work with infrared
> > countermeasures also have labels for specific infrared bands just as radar
> > engineers have names for radar bands (VHF, UHF, L band, S band, C band, X
> > band Ku band, K band, Ka band, etc). Radar countermeasure engineers have
> > different names for these same radar bands (A through M bands). Names can
> > sometimes be ambiguous. On the other hand, we do know about silicon
> > detectors. All CCD manufacturers publish the quantum efficiency of their
> > silicon CCD cameras. It is a fact that intrinsic silicon only works out
>to
> > about 1000 nm (or ~1 micrometer, beyond the visible to include a part of
> > the near infrared). This is determined by the energy band gap of silicon
> > and the energy in a single photon.
> >
> > The point is not the name of the band, but rather whether a
>cooled
> > or uncooled silicon CCD camera can detect photons emitted by a live human
> > hand. There simply are too few photons to measure in the band in which
> > silicon is sensitive. There is no arguing this point. It is as true as
> > any other scientific fact. Stating otherwise reveals a lack of
> > understanding of the physics of blackbody emission. The same physics that
> > allows one to measure the surface temperature of the stars by measuring
>the
> > color of the stars. The number of photons emitted by a blackbody at a
> > specified temperature is easily calculated by integrating the Planck
> > function across the band of interest and applying the details of the
> > optical system, detector quantum efficiency and detector noise
> > sources. Performing a simple experiment should demonstrate this, if the
> > experiment is done correctly and the results are interpreted
> > correctly. Remember the early failed attempts to measure the speed of
>light!
> >
> > The beauty of science is being able to mathematically predict the
> > outcome of experiments based on earlier observations and the theories that
> > have been developed from these observations.
> >
> > Bill Keicher
> >
> >
> >
> > At 01:59 PM 4/23/2004 -0500, you wrote:
> > >I always thought it was called the near infra red. This is shorter
>than
> > >thermal energy by quite a bit.
> > >
> > >I the farther infra red, silicon and gallium are actually used as lens
> > >elements. These materials are transparent to far IR radiation. I think
> > >most optics, such as used for heat seeking missiles and the like work in
>the
> > >far infra red. That is, thought wavelengths longer than several microns.
> > >The radiation called IR really has several regions because it is a very
> > >large range. I would suppose IR goes way out to the region of very
>short
> > >micro waves of a fraction of a millimeter.
> > >
> > >There is a continuum of electromagnetic wavelengths of course. When I
>was
> > >in school, we called millimeter waves and shorter, very short indeed! (G)
> > >
> > >Doc G
> > >
> > >
> > >----- Original Message -----
> > >Sent: Friday, April 23, 2004 12:37 PM
> > >Subject: Re: [M]: 201XT Problems...Dual Brightness Readings?
> > >
> > >
> > > > Then why do consumer digital cameras and webcams have IR blocking
>filters?
> > > > What do you call the part of the spectrum between about .7 to 1.1
>micron?
> > > > -John
> > > >
> > > >
> > > > >Subject: Re: [M]: 201XT Problems...Dual Brightness Readings?
> > > > >Date: Fri, 23 Apr 2004 00:43:33 -0400
> > > > >
> > > > >No, that fact has never been true. CCDs are not "typically very
> > >sensitive
> > > > >to
> > > > >IR", they have NO sensitivity to IR. They never have. This is the
>usual
> > > > >urban
> > > > >legend nonsense, the result of repeating crap from one web site to
> > > > >another,
> > > > >totally unsupported by any measurement. People here should know
>better.
> > > > >It's
> > > > >a silicon detector and has no sensitivity beyond about 1.1 micron.
> > > > >
> > > > >Peter
> > > > >
> >
> >
> >

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