Re: [APML] Need a little education

["Bert Katzung" <katzung1@attbi.com>]

Hi Don:
The concept is pretty simple, the full picture is not so simple. The red
line in your graph shows the percent of light passed (vertical axis,
ordinate) at the wavelengths shown on the horizontal axis (abscissa). So,
for example, the filter blocks light around 440 nM wavelength (a bluish
wavelength) as shown by the red line dropping down to near zero. Each of
these notches (560, 590, 630, etc nM) represents a range where little or no
light gets through. Why do they engineer the coating this way? Because the
light polluting sodium and mercury vapor lamps on our streets (and other
sources) are putting out a lot of light at those wavelengths. On the other
hand, the filter is passing most of the light coming from important astro
sources. You can see a chart of these wavelengths on my website at
http://www.astronomy-images.com/Articles/EmissionLines_etc/EmissionLines-1.h
tm
Hope this helps...
Bert

Bert Katzung
katzung1@attbi.com
www.astronomy-images.com

----- Original Message -----
From: "Don Spencer" <ecdon@cox.net>
To: "Discussion of Film Astrophotography" <astro-photo@seds.org>
Sent: Wednesday, April 16, 2003 4:27 PM
Subject: [APML] Need a little education


Hi all,
          I hope someone can help me here. I just received a 48mm IDAS LPS
filter from Huetec. It came with the following chart..
http://members.cox.net/ecdon/IDAS%20LPS.jpg
Being the "Light" dummy that I am, I have no idea what this is telling me.
If someone would explain it to me, I'd really appreciate it. *L*
Thanks,
Don Spencer



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