On Mon, 17 Aug 2009 18:28:47 -0700, John Larkin
jjlarkin_at_highNOTlandTHIStechnologyPART.com> wrote:
On Mon, 17 Aug 2009 17:44:26 -0700, Archimedes' Lever
OneBigLever_at_InfiniteSeries.Org> wrote:
On Mon, 17 Aug 2009 08:28:35 -0700, John Larkin
jjlarkin_at_highNOTlandTHIStechnologyPART.com> wrote:
On Mon, 17 Aug 2009 13:18:36 +0100, Martin Brown
|||newspam|||@nezumi.demon.co.uk> wrote:
Archimedes' Lever wrote:
On Sun, 16 Aug 2009 11:11:46 -0700, John Larkin
jjlarkin_at_highNOTlandTHIStechnologyPART.com> wrote:
On Sat, 15 Aug 2009 10:05:24 -0700, Archimedes' Lever
OneBigLever_at_InfiniteSeries.Org> wrote:
On Fri, 24 Jul 2009 20:00:33 -0700, Archimedes' Lever
OneBigLever_at_InfiniteSeries.Org> wrote:
At the same time, Fischer Price sold a B&W "toy" camera for $150 that
could have a Ge or Pyrex lens or filter put on it, and it would do IR
very nicely.
Perfect proof that most in the group are idiots.
Not one comment on this well known anomaly as the years ticked by.
The FP uses a CCD so can't work as a thermal imager. Near IR, maybe,
but that isn't germanium lens territory.
"Can't work"? You're an idiot. The first IR imagers were CCD. They
came out before CMOS image planes were even around.
I'm with John on this one. The first CCDs were largely in the visible
with a strong peak sensitivity in the *near* IR and with a very big push
to get them out to much longer wavelengths on somewhat exotic materials.
I knew an astronomy imaging group that were given new military chips to
test because they could turn one into a fully working prototype camera
way faster and cheaper than the approved contractors.
Rough graphs of the typical sensitivity for silcon CCDs with front and
back thinned window construction are online at:
http://www.andor.com/learn/digital_cameras/?docid=315
Their response does not extend much beyond 1000nm which is still an
order of magnitude short of the roughly ~10um IR wavelengths needed for
thermal imaging at ambient temperatures.
Eventually they did get longer wavelength CCDs working, and they stopped
at a particular point. As the man said "what we have is good enough to
see what *we* need to see". Astronomers were a bit disappointed that
after that they had to pay for their own chip R&D. It didn't stop
terahertz sensors eventually being made though. Strangely the terahertz
image of my favourite object Cass A appears to have been removed from
the web.
As for the lenses, they are specifically for narrowing a spectral
response.
http://www.thorlabs.com/images/TabImages/GermaniumTrans.jpg
OK. So you found a site that gave you a good picture of what passes
through Germanium. So what?
Most digital cameras work nicely in the near IR.
So what? The FP device did as well. All that was needed was a bit of
gain increase after placing the filter.
That only gets you near infra red. The thermal band for things in the
temperature range 0-100C is much more tricky and generally involves
exotic doped materials, germanium lenses and cunning optical design
since the emissions from the casing start to be almost as bright as the
target. Some form of multistage thermoelectric cooling is usually
employed or LN2.
Regards,
Martin Brown
CCD detector + germanium lens = zero response.
John
You + logic = water + oil.
So do you think that a germanium lens would make the FP toy into a
thermal imager?
Yes or no?
John
A window does not "make" anything into anything. Windows are used for
filtration, just like say a "bandpass filter".
The camera has optics already. All it would need is a windows of the
appropriate spectral range for the desired intended use.
