Re: [ATM] Infrared Scope Design

[Dominic-Luc Webb <dlwebb@canit.se>]

Well, not sure where to begin this discussion. No it is not stupid
at all if your aim is to measure in the IR. The UBV system was
extended a while back to include RI (UBVRI), and then came more,
I think they are J, K,L, and maybe M with increasing wavelength.
You must consider where the scope will be situated and I know
some people in here are have some excellent locations. You will
need to consider the atmospheric absorbance spectrum and relate
this to the strength of the signal from your targets. I do not
think you should plan on sensitive measurements of the cosmic
radiation background from the big bang, for instance. That kind
of data comes from satellites like COBE:

http://www.astro.ucla.edu/~wright/CIBR/

Compare that, to these instruments that are ground based on
very dry mountain tops, some in California where a lot of
ATM's, maybe eve4n you, are located:

http://www.ipac.caltech.edu/Outreach/Edu/ground.html

I looked into this a while back because it looked like a fun
niche where most other amateur astronomers never go. As for
coating, I think Dale is probably right as for the lower IR,
but the UV mirrors I know of are coated with other materials,
so I would imagine at some point there is a difference
between Au and Au that justifies the added expense.

Detectors: Well not all CCDs are equal, but they generally
are very sensitive in the IR, which actually presented a
problem in the early CCD days because the commercial market
wanted to take snapshots in the visible. As I understand it,
most CCDs have filters to drop down the IR sensitivity to
make it more color neutral. For highly sensitive measurements,
there are very good IR PMTs these days. You can also consider
a bolometer. I think I once found clues about how to make a
homemade bolometer years ago at the Harvard ADS database
where you can find a lot of IR articles:

http://adsabs.harvard.edu/abstract_service.html

My first really sensitive IR detector was a IR receiver from
a TV. I could calibrate with the remote. These are AC as I
remember, so there are some linearity issues, but some TVs
have really sensitive IR sensors. Some years back, they
were orders of magnitude more IR sensitive than a webcam,
for instance. I never got round to comparing to a professional
IR photometric CCD, but I could guess the TV sensors are still
quite sensitive by comparison, and darned cheap! Of course,
these sensors come in arrays nowadays, and for comparison,
CCDs can be binned. Not sure who the winner would be, but
the price is clearly in favor of homemade.

Dominic



On Wed, 10 Oct 2007, Jacob Lauser wrote:

> This may sound stupid, but what's to stop an ATM from building a scope
> with a gold-coated primary and using an SBIG CCD to do infrared
> astrophotography?
>
> I assume that all you would need is an appropriate infrared filter and
> that the CCD could be still used to take such images. Is that
> feasible?
>
> Any comments? Suggestions?
>
> - Jake L.
> _______________________________________________
> ATM mailing list http://www.atmlist.net/
>

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