Optolong L-eXtreme Dual Bandpass Light Pollution Reduction Imaging Filter - 1.25"

Dual narrowband 1.25” filter for high-contrast imaging of emission nebulae, planetary nebulae, and supernovae remnants
Narrow 7nm passbands for OIII and H-alpha and rejection of light pollution and scattered moonlight for maximal image contrast
Electron-beam gun evaporation with ion-assisted deposition coating technology for durability and resistance to scratching
Precision ground and polished for superior image quality

A. About Optolong's L-eXtreme Filter

The Optolong 1.25” L-eXtreme filter builds on the success of the renowned L-eNhance filter to deliver an even higher degree of contrast when imaging emission nebulae, planetary nebulae, and supernovae remnants. The L-eXtreme is two filters in one. It has a narrow 7nm passband centered on H-alpha at 656nm and a second 7nm passband centered on OIII near 501nm. The majority of nebulae have their strongest emission at these two wavelengths.

Unlike the L-eNhance filter, the L-eXtreme blocks the weaker H-beta emission line at 486nm to deliver more contrast in the fainter regions of nebulae, even in light-polluted sky. The narrower passbands of the L-eXtreme are especially important in blocking moonlight and broadband light pollution found in many urban and suburban centers.

The L-eXtreme is an ideal filter for use with DSLRs, one-shot color (OSC), and monochrome CCD and CMOS cameras, especially with fast optical systems. It’s an indispensable filter for urban and suburban astrophotographers and for everyone who likes to extend their imaging sessions into nights when the moon is bright.

B. Spectral Curve Transmission Characteristics

FWHM: 7nm at O-III and 7nm at H-a
Blocking range: 300 - 1000nm
Light pollution line blocking depth: > 99%

C. Technical Specifications

Both surfaces are fine optically polished, accurate to 1/4 wavelength or better, and parallel to within 30 seconds or arc.
1.85mm thick Schott B270 optical glass substrate material.
Very high surface quality of 60/40 or better (US Military Spec MIL-O-13830).

D. Optical Coating Specifications

Multi layer anti-reflection coated.
Non-cementing optical substrate coating.
Electron-beam gun evaporation with Ion-assisted deposition coating technology for durability and resistance to scratching, as well as stability on CWL (central wavelength) so that there is no deviation due to temperature changes during use.
Precise and homogeneous coatings ensure high values of desired passband and blocking of unwanted offband.
Every single filter is tested and passed by Optolong before shipping to dealers.

E. Other

1.25" astronomy filter with standard M28.5x0.6 male filter thread (no female thread, so it cannot be stacked with other filters).
Ultra-thin filter cell to minimize vignetting; clear optical aperture of 26mm.
Precision CNC-machined metal filter cell with sand blasted black anodized finish, anti-reflection treatment, and laser engraving.
High quality protective plastic storage case.

WARNING: Optolong filters are not designed for direct solar observation. NEVER use these filters for observing the Sun, or permanent eye and equipment damage will result.

F. Sample Images and Comparisons

1. Compare L-eXtreme vs No Filter

Object: M42
Date: 15-16 March 2020
Location: Hong Kong - Shatin (Light pollution level 7~8, City center, light pollution disaster area
Camera: ZWO ASI183MC Pro
Telescope: Sky-Watcher N130/650 f/5 with coma corrector
Filter: Optolong L-eXtreme 2"
Mount: iOptron CEM25EC
Guide: 120mm mini guide scope, ZWO ASI120MM mini
Copyright: © Vincent Cheng (Hong Kong)

2. IC1396 (Elephant Trunk Nebula) to Sh2-129 (Flying Bat Nebula)

The Optolong L-eXtreme is two 7nm filters in one: H-Alpha and OIII. The filter is a powerful tool for isolating these two important nebula lines against the effect of light pollution and moonlight, and it saves time by allowing capture of both bands in a single frame. Ideal for use with monochrome and color astronomy cameras and DSLRs.

Location: La Jonquera, Girona, Spain
Date: April 2020
Camera: Canon 6D mod
Telescope: WO SpaceCat 51
Mount: Sky Watcher EQ6 Mount
Guide: Guide camera QHY5
Image Details:
- RGB 25 x 600" ISO 3200 - Optolong L-Pro
- H-Alpha & OIII 20 x900" ISO 3200 - Optolong L-eXtreme
- Flats, Darks & Bias
Copyright: © Jose Jiminez

3. M8 (Lagoon Nebula) © Vincent Cheng (Hong Kong)

Date: 30 April and May 1 2020
Location: Lower Shing Mun Reservoir, Shatin, Hong Kong (Bortle scale: level 7~8)
Camera: ZWO ASI183MC Pro (cooled at -10C)
Telescope/Lens: SVBONY SV48 (500mm f5.5)
Filter: Optolong L-eXtreme 2" Prototype
Tracking Mount: Sky-Watcher AZ-GTi
Controlled through ASIAIR PRO and SkySafari 6 plus
Autoguide: 120mm mini guide scope, ZWO ASI120MM mini
Total Exposure Time: 5mins X 21frames with Dark Frames, Processed with PI, PS CC
Copyright: © Vincent Cheng (Hong Kong)

China

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