erick
23-07-2007, 05:12 PM
I was kindly lent (thanks Janoskiss) a 1.25" DGM Optics NPB filter to try out in my 8" f6 reflector. I'd followed a few threads/reviews, looked at various filters and was interested in the good reports of this filter relative to its very economical price, compared with the standards - Skyglow, OIII, UHC, Deepsky, Ultrablock etc.
DGM Optics (Seems to be only through the Omega Astrofilters site http://www.omegafiltersebuyer.com/servlet/the-NPB-Filters/Categories ) says:-
"The NPB (Narrow Pass Band) filter is an Ultra High Contrast type of filter that is very effective for small and fainter emission and planetary nebula and a variety of bright nebula, especially through larger scopes."
I had two opportunities to use the filter last weekend. One under dark sky conditions after the Moon had set and one in misty skies under quarter moonlight. I used it with a 15mm Bintel (GSO) plossl and a Vixen LV 10mm eyepiece. Targets were Carina Nebula, Lagoon Nebula and Triffid Nebula.
Now, if you are expecting an expert assessment - sorry - I don't have the experience, but on one night I did have a more experienced observer with me.
My summary - I thought it was very useful. It clearly darkened the sky relative to the nebulae. Edges of a nebula were more clearly distinguished. In the moonlit sky, Carina and Lagoon were better distinguished with the filter (didn't look for Triffid that night). Under dark sky, I could convince myself that I could make out the dark lanes in Triffid. Now, the more experienced observer agreed that there was better contrast between the nebulae and the background, but thought that some of the detail of the nebulae was being lost. Light transmission seemed good, the nebulae weren't noticeably darker with the filter in place. I did notice that the focus point changed with the filter in place.
It had an interesting effect on Eta Carina - it went deep red. For fun, I turned the scope on Antares which was also a deep red colour.
All I can say is that I'd like to get one - the 2" version so I can drop the magnification to gather the whole view. Those who have no use for their 2" DGM Optics NPB filter - you might have a sale! (See the classifieds)
DGM Optics (Seems to be only through the Omega Astrofilters site http://www.omegafiltersebuyer.com/servlet/the-NPB-Filters/Categories ) says:-
"The NPB (Narrow Pass Band) filter is an Ultra High Contrast type of filter that is very effective for small and fainter emission and planetary nebula and a variety of bright nebula, especially through larger scopes."
I had two opportunities to use the filter last weekend. One under dark sky conditions after the Moon had set and one in misty skies under quarter moonlight. I used it with a 15mm Bintel (GSO) plossl and a Vixen LV 10mm eyepiece. Targets were Carina Nebula, Lagoon Nebula and Triffid Nebula.
Now, if you are expecting an expert assessment - sorry - I don't have the experience, but on one night I did have a more experienced observer with me.
My summary - I thought it was very useful. It clearly darkened the sky relative to the nebulae. Edges of a nebula were more clearly distinguished. In the moonlit sky, Carina and Lagoon were better distinguished with the filter (didn't look for Triffid that night). Under dark sky, I could convince myself that I could make out the dark lanes in Triffid. Now, the more experienced observer agreed that there was better contrast between the nebulae and the background, but thought that some of the detail of the nebulae was being lost. Light transmission seemed good, the nebulae weren't noticeably darker with the filter in place. I did notice that the focus point changed with the filter in place.
It had an interesting effect on Eta Carina - it went deep red. For fun, I turned the scope on Antares which was also a deep red colour.
All I can say is that I'd like to get one - the 2" version so I can drop the magnification to gather the whole view. Those who have no use for their 2" DGM Optics NPB filter - you might have a sale! (See the classifieds)