Rob_uk
newbie
Reged: 12/30/07
Posts: 1
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I bought a Lumicon UHC filter around a year ago, and started to notice that many stars were very obviously blue coloured.
Now, the stars that turned blue with the filter in place did not remain blue when the filter was remomved.
After doing a small amount of research I read that stars pecieved as blue through the filter had a nebulouscity surrounding them.
Is this true?
Rob
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Meade 8" LX-90
Revelation 15x70 Bino
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walt r
Post Laureate
Reged: 02/13/07
Posts: 3611
Loc: Doylestown, PA
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Not necessarily. Many stars emit light in a fairly continous spectrum from IR throught UV. The UHC filter only passes light in the blue/green (H beta and OIII, ~480 to 510nm wavelength). Therefore only the star's light that is in the blue/green will pass through the filter and the star looks blue/green. Other stars emit more toward the red end of the spectrum. These stars emit very little blue light. The UHC filter attenuates the yellow through red light and they dim considerably. Whereas other stars have emit more toward the blue. These are attenuated less by the UHC filter so they don't appear to dim.
Here is a link that shows the spectra through different filters.
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Walt
Obsession 18" f/4.45 #1370 AN/SC
MK67 Deluxe 6" f/12 Mak-Cass, Super Polaris GEM, JMI MicroMax DSC
DIY 60mm f/6 Achromat
Cookbook 245 CCD
Edited by walt r (12/30/07 05:02 PM)
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Starman1
Vendor (EyepiecesEtc.com)
Reged: 06/24/03
Posts: 17639
Loc: Los Angeles
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Nebulae that appear bluish are typically reflection nebulae, and reflect the spectra of the stars near them. Since those stars emit light in broad ranges of wavelengths, a UHC filter will usually dim reflection nebulae.
Emission nebulae, on the other hand, tend to concentrate their outputs in a few discreet frequencies, so the UHC filter will significantly enhance the visibility of those nebulae. They include most large nebulae and planetary nebulae.
The most common emission wavelengths are:
H-Beta at 486nm
O-III at 496nm
O-III at 501nm
H-Alpha at 656nm
The H-alpha is in the very deep red, where our eyes are relatively insensitive to light. That's why the UHC filter doesn't typically pass that wavelength, even though the wavelength is a strong emission.
A UHC filter passes all of the first 3 wavelengths.
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Don Pensack
www.EyepiecesEtc.com
12.5" Teeter/Zambuto, 5" Maksutov
Sustaining Lifetime IDA member
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