Optolong L-eXtreme Light Pollution Dual-Bandpass Narrowband Imaging Filter - 2"

product code: OPT-L-eXtr-2
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Optolong L-eXtreme Light Pollution Dual-Bandpass Narrowband Imaging Filter - 2"

Optolong L-eXtreme Light Pollution Dual-Bandpass Narrowband Imaging Filter - 2"

The Optolong L-eXtreme 2" filter is a dual-bandpass narrowband filter designed for light polluted skies to maximise the output from your imaging time. It offers even higher contrast than the popular L-eNhance filter due to the narrower bandwidths at both parts of the spectrum, H-alpha and OIII. 

Optolong came out with their latest development that offers a more extreme dual-narrowband solution in comparison to their very popular L-eNhance filter. Both the L-eNhance and L-eXtreme are Dual-bandpass filters as they let through the light in two sections (bands), however, to distinguish between the L-eNhance and the latest L-eXtreme filters, we had to rename the L-eNhance to a triple-band filter. Both filters have two bands, but the L-eNhance lets through the light coming from three important emission light sources (H-Alpha, H-Beta, and Oxygen III), whilst the L-eXtreme focuses on two important emission light sources only (H-Alpha and Oxygen III), hence the change of title for the L-eNhance filter.

In the L-eXtreme you have two very narrow bands at 7nm each. The bandwidth of the H-alpha  part is similar in both filters (although it is somewhat narrower in the L-eXtreme), but in the L-eXtreme now we have an extremely narrow band at 7nm for the OIII as well. 

The relentless spread of urbanization and its associated light pollution have become a growing problem for all amateurs and astro photographers. The current solutions to the problem can be expensive and might include the purchase of a monochrome camera, several types of narrowband filters and a filter wheel.

L-eXtreme, similarly to the popular L-eNhance provides an economical and practical solution for amateurs. It is a dual-band pass filter which has been designed for DSLR (digital SLR), colour CMOS and colour CCD cameras. The convenience and cost effectiveness of this filter allows amateurs to image a rich selection of astronomical images, even in bright, heavily light-polluted areas. 

Optolong believes the design of our L-exTreme filter is a technical innovation among filters. It effectively isolates the H-Alpha and Oxygen III nebula emission lines whilst blocking out 99.9% of light pollution and achieves a maximum transmission of over 93%. As a result, contrast and signal-to-noise ratio from the nebulosity is maximised. The performance of this filter delivers images that superbly control the impact from light polluted skies.

L-eXtreme Filter Spectrum Curve

According to the characteristics of celestial body emission lines and feature of light pollution span of spectrum, Optolong specially designed and optimized the dual-band L-eXtreme filter in order to retain the prominent color of nebula RGB while blocking out nearly all of the light pollution. Spectrum as shown below:

Substrate: B270 (high quality optical glass)
Thickness: 1.85mm
Tpeak: T>92-93%
Blocking range: 300-1000nm
Blocking depth: light pollution  line blocking >99.9%
Surface quality: 60/40
Transmitted Wavefront RMS: λ/4
Parallelism (arcsec): 30"

L eNhance Filter curve

The Major Emission Lines of Nebulae: H-α 656.3nm, H-β486.1nm, OIII 495.9nm, OIII 500.7nm 
The Major Emission Lines of Artificial Light Pollution: Hg 435.8nm, 546.1nm, 577nm, 578.1nm, Na 598nm, 589.6nm, 615.4nm, 616.1nm

Optolong will continue to optimize the product according to actual testing, therefore the above curve is not to be used as the final product data.

Available Sizes

1.25” mounted and 2” mounted are available now.
Other sizes will be listed when become available.

Sample photos

Object: M42

Time : 15th.--16th. March 2020

Place: HongKong-Shatin

Camera : ZWO ASI183MC Pro 

Telescope : f/5 @ Sky-Watcher N130/650 w coma corrector

Filter : Optolong  L-eXtreme 2"

Mount : iOptron CEM25EC

Guide : 120mm mini guide scope, ZWO ASI120MM mini

Light pollution level 7~8(City center, light pollution disaster area

Copyright: ©Vincent Cheng (Hong Kong)

Object:NGC6946, Barnard 150 & Sh2-129 Flying Bat nebula

Equipment:Canon 6D mod+WO SpaceCat 51+Optolong L-eXtreme&L-Pro

Data:RGB 25 x 600" ISO 3200 - Optolong L-Pro

H-Alpha & OIII 20 x 1500" ISO 320 0 - Optolong L-eXtreme

Copyright: ©José Jiménez (Spain)

Package Details 

  • Silver cardboad box
  • Plastic PP box
  • Imported high pressure EVA case lining
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Brand Optolong
Condition New
Product Code OPT-L-eXtr-2