Optolong L-Ultimate 3nm Dual-Band Filter - 2" 

The L-Ultimate is a 3nm dual band filter designed to drastically reduce the effect of light pollution. The 3nm isolates the nebulae's emissions into H-Alpha (red) and OIII (green-blue). It blocks light pollution, maximizes the signal from nebulae, and darkens the sky background. It also blocks artificial light from mercury vapor lamps, high and low pressure sodium vapor lights, and unwanted natural light caused by the emission of neutral oxygen in our atmosphere, maximizing the transmission of the main emission lines of the nebula in OIII (496nm and 500nm) and H-alpha (656nm). Used with DSLR, color/MONO CMOS and CCD, this filter is suitable for telescopes with an f-ratio of f/4 or higher (slower).

The advantage of L-Ultimate is that it only passes through the emission lines OIII (500.7nm) and H a(656.3nm), in which case all other light pollution emission lines are eliminated so that only the emission and reflection signals of the nebula are captured during imaging. Therefore, the sky background of the image is darker, and the contrast between the nebulae and the signal-to-noise ratio are improved to the greatest extent. In heavy light pollution areas, the product can also selectively filter light pollution and clutter signals through the emission lines of nebulae, and finally avoid the impact of light pollution on astrophotography.

The L-Ultimate is different from the series of dual-narrowband L-eNhance and L-eXtreme in that the L-Ultimate is a dual-3nm bandwidth filter that only passes through Ha and OIII emission lines. You will get a darker sky background, more contrast of the image and the suppression on stars. L-Ultimate has also been optimized in terms of halo performance, so that there is no obvious halo when shooting on a bright star object.

According to the characteristics of celestial body emission lines and feature of light pollution span of spectrum, Optolong specially designed and optimized a dual 3nm narrowband filter in order to retain the prominent color of nebula at OIII and Ha while blocking the light pollution. Spectrum shown in the fourth photo above.

Specifications:

• Substrate: Optical Glass
• Size: 2" mounted (M48x0.75 thread)
• Thickness: 1.85mm
• FWHM: OIII 3nm, Ha 3nm
• Blocking Range: 300-1000nm
• Blocking: OD4
• Surface quality: 60/40
• Transmitted Wavefront RMS: λ/4
• Parallelism: 30seconds

About Optolong

While Optolong is a relative newcomer to the astronomy industry, they are no strangers to optics and filters. Optolong is a division of Yulong Optics Company, a high tech company specializing in optical filter design and production. Their products include bandpass filters, flourescence filters, edge filters, longpass and shortpass filters, beam splitters, anti-reflection coatings, optical mirrors and, of course, astronomical filters.

Established in 1999 and based in Kunming City, China, Optolong/Yulong provides nearly 2000 types of optical filter coatings annually to customers worldwide in a wide variety of industries and applications.