Castell UHC Ultra High Contrast Filter, 1.25"
Castell UHC Deepsky Filter for 1.25-Inch (31.7 mm) Eyepieces
This UHC filter allows emission lines of H-alpha, H-beta, S-II and O-III where most of the light comes from in the case of emission nebulae.
On the contrary it will cut off all the light produced by Mercury and Sodium lamps that is important for astronomers in light polluted areas. The result is a darker background with higher level of contrast for our main astronomical objects such as nebulae. Deep sky objects will appear to be brighter and stars to be fainter, even though it's a visual illusion as merely the background became darker.We would recommend to buy a plastic carry case as well that is otherwise not included:
White Transparent Plastic Filter Case
Courtesy of Paul Hunter. Above image has been taken via a Castell 2" UHC filter by Paul Hunter with his Skywatcher Explorer-200P Newtonian telescope (f/5, 1000mm focal length), mounted on Skywatcher EQ5 mount without guiding, he also used a Baader MkIII Coma Corrector
NGC7635 Bubble Nebula (Left) & M52 Open Star Cluster (Right), 1 hour 15 minutes total exposure. (75 x 1 minute frames), 1600 ISO, 40 Dark frames, 45 Bias frames, No Flat frames, Stacked in DSS and processed in Photoshop. Camera used: Nikon D5300 dSLR (un-modified).
here is another wonderful image by Paul Hunter, taken by using the same equipment.
Courtesy of Paul Hunter. Click on the image for a higher resolution image at 1200px wide.
M1 Crab Nebula, 32min 15 sec total exposure (56 frames), 1600 & 2500 ISO. Camera used: Nikon D5300 dSLR (un-modified).