I haven't heard anything about the DGM Galaxy Filter. Does this help? Do you have any filters you think help galaxy observing from light polluted areas?
What is the latest word on Galaxy Filters?
Started by Williamsburg, 04/11/2007 01:28AM
Posted 04/11/2007 01:28AM
Opening Post
Posted 04/11/2007 07:36PM
#1
Have NOT heard a thing... :S
So far, only Dark Skies will give me THE VIEWS... (but hopefully a filter will show up soon) 8)
Clear skies!
So far, only Dark Skies will give me THE VIEWS... (but hopefully a filter will show up soon) 8)
Clear skies!
Ivan Gastaldo 8)
Coconut Creek, FL
Ivan's Observatory
Lat 26N 16' 48" Long 80W 10' 48"
[COLOR="Red"]Personal Website:[/COLOR] http://www.ivangastaldo.com
CCD Imaging and Processing/Deep Sky - Moderator
I like to complain about everything - Moderator
Posted 04/12/2007 08:33PM
#2
Just posted on Cloudynights:
http://www.cloudynights.com/item.php?item_id=1646
Joplin
http://www.cloudynights.com/item.php?item_id=1646
Joplin
Posted 04/13/2007 05:52AM
| Edited 04/13/2007 05:53AM
#3
My personal opinion: I don't believe that it is possible to make a galaxy filter with any significant efficiency today. Any filter works by blocking out part of the electromagnetic spectrum. The intensity of undesired light is strongly reduced while (almost) all the light of the celestial object is allowed to pass. If the desired and undesired light have strongly different spectral distribution, the filter will work. This is the case for emission nebulae, since they emit a very large amount of their visible light within a small wavelength band.
Galaxies have a more or less continuous spectrum, not very different from sunlight (emission and absorption lines are there, but they don't contribute significantly and are spread over the enitre spectrum). Undesired light may differ from place to place, but my impression is that high-pressure sodium lamps make the strongest contribution at most urban places in the western world. The spectrum of these lamps somewhat differs from galactic light, but they emit some radiation almost across the entire spectrum, making this light almost impossible to filter away.
I'm old enough to remember the time when low-pressure sodium lamps were used. This light would have been possible to block out since almost 100% of the radiation came from a double spectral line in the orange-yellow part of the spectrum.
Mercury lamps also emit almost all their light at a few wavelengths within the visual spectrum. Unfortunately they are spread over almost the whole spectrum, and an efficient mercury-lamp rejection filter would be very expensive to make.
I hate high-pressure sodium lamps.
Inge S
Galaxies have a more or less continuous spectrum, not very different from sunlight (emission and absorption lines are there, but they don't contribute significantly and are spread over the enitre spectrum). Undesired light may differ from place to place, but my impression is that high-pressure sodium lamps make the strongest contribution at most urban places in the western world. The spectrum of these lamps somewhat differs from galactic light, but they emit some radiation almost across the entire spectrum, making this light almost impossible to filter away.
I'm old enough to remember the time when low-pressure sodium lamps were used. This light would have been possible to block out since almost 100% of the radiation came from a double spectral line in the orange-yellow part of the spectrum.
Mercury lamps also emit almost all their light at a few wavelengths within the visual spectrum. Unfortunately they are spread over almost the whole spectrum, and an efficient mercury-lamp rejection filter would be very expensive to make.
I hate high-pressure sodium lamps.
Inge S
Posted 04/22/2007 10:03PM
#4
Speaking as a chemist with nearly 40 years of experience - much of which involved spectroscopy- it is a know fact that ANY object - be it a galaxy,or street light, for example, CAN and DOES emit light at different intensities at different wavelength of both the visible and UV spectra.
In similiar fashion ANY filter CAN and DOES absorb different amounts light at any given wavelength(nm).
IMHO, to say that no filter will improve visibility of any galaxy ignores the above laws of physics.
At the same time, to say that any one filter works best on surpressing light pollution from all areas of the world ignores the fact that viewing sights differ in terms of specific light pollution - even from night to night.
We don't make the laws of physics, but we would be wise to heed them.
Clear skies....... Mike A
In similiar fashion ANY filter CAN and DOES absorb different amounts light at any given wavelength(nm).
IMHO, to say that no filter will improve visibility of any galaxy ignores the above laws of physics.
At the same time, to say that any one filter works best on surpressing light pollution from all areas of the world ignores the fact that viewing sights differ in terms of specific light pollution - even from night to night.
We don't make the laws of physics, but we would be wise to heed them.
Clear skies....... Mike A
Funding Member
