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MikeBu
super member
Reged: 12/04/07
Posts: 122
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Re: Using a Nightime H-Alpha filter for Solar view
04/24/08 04:55 PM
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I was curious so I crunched some numbers on the solar spectrum.
Bandwidth
......
...
..
Power
..........Spectrum
200nM - 10,000nM
...
...
1.37 kW/sq.M.............(IR - UV)
380nM 750nM
..........531 W/sq.M.............(Visible)
655.8nM 656.8nM
...
...
1.12 W/sq.M.............(1.0 nM Red around H-alpha)
656.2050nM 656.3550nM...
.
..75.2mW/sq.M.............(1.50 Angstrom, H-alpha)
656.2300nM 656.3300nM...
.
..35.7mW/sq.M.............(1.00 Angstrom, H-alpha)
656.2425nM 656.3175nM...
.
..22.9mW/sq.M.............(0.75 Angstrom, H-alpha)
656.2455nM 656.3050nM...
.
..14.1mW/sq.M.............(0.50 Angstrom, H-alpha)
The minimum at H-alpha is approx. 16.04% the local maximum (i.e. Plank curve). At 0.75 and 0.50 Angstroms the ratio of bandwidths is close to the ratio of the powers indicating the spectral density is getting pretty flat.
Comparing the 1nM (10 Angstrom) band to the 1.00 Angstrom band the 1nM band has 31.4 times the light, more than enough to mask the H-alpha emission spectrum. Not that I didnt believe everyone here, but just to get some perspective.
For a 100mm scope aperture with no white filter, the 1nM filter will need to dissipate 10.8 Watts. The level through just the 1nM filter would still be 8.8mW, brighter than looking into a red laser pointer. Even if the level of light through a nighttime filter was eye safe without a white filter it probably couldnt dissipate the power and would fail in a very unpleasant way.
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