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Optolong L-Extreme Filter

Optolong L-Extreme Filter

by Optolong
SKU OPT-13901
CA$335.00 - CA$432.00
CA$335.00
CA$335.00 - CA$432.00
CA$335.00
Price Match Policy!
  • Narrow dual-bandpass filter for H-Alpha and OIII
  • Blocks >99% of light pollution emission lines
  • Peak transmission of >90% at critical wavelengths
  • Transmitted Wavefront RMS of λ/4
  • 1.85mm thick B270 substrate with 30s parallelism
1 in stock
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  • Description
  • FAQ
  • Specifications
  • Warranty

  • Optolong L-Extreme Filter

    The Optolong L-Extreme Filter isolates critical nebula emission lines with over 90% peak transmission while blocking more than 99% of common light pollution sources. Built on a 1.85mm B270 substrate, its λ/4 transmitted wavefront and 30s parallelism ensure your optical system's native resolution is maintained. This narrow dual-band design simultaneously captures H-alpha and Oxygen III, maximizing contrast for one-shot color and monochrome cameras operating under bright urban skies.

    A Dual-Band Design for >99% Light Pollution Suppression

    The L-eXtreme isolates the two most important emission lines for most nebulae—Hydrogen-alpha and Oxygen III—on a single filter. By aggressively blocking wavelengths outside these passbands, including a >99% rejection of artificial light pollution, the filter produces a dramatic increase in contrast between your target and the skyglow background. This allows you to capture clean, detailed data even from severely light-polluted locations or during bright moonlit nights.

    Optimized for Fast Optics and One-Shot Color Cameras

    Modern fast optical systems, such as f/2 RASA or HyperStar setups, place high demands on filter performance. The L-eXtreme is engineered to minimize band-shift with these steep light cones, ensuring consistent transmission and color balance. For imagers using one-shot color cameras like DSLRs or dedicated CMOS astronomy cameras, this filter is a cost-effective and convenient way to produce detailed bicolor images without the need for a filter wheel and monochrome setup.

    λ/4 Wavefront Accuracy and Durable Ion-Assisted Coatings

    A filter should never degrade the quality of your telescope's optics. The L-eXtreme is manufactured to strict tolerances, with a transmitted wavefront of λ/4 and parallelism of 30 arcseconds, preventing any introduction of aberrations or distorted star shapes. The multi-layer coatings are applied using an advanced ion-assisted deposition process, creating a durable, scratch-resistant surface that provides wavelength stability regardless of temperature changes during an imaging session.

    Optolong L-eXtreme vs. L-eNhance: The Tri-Band Trade-Off

    The primary difference lies in their bandpass strategy. The L-eNhance is a tri-band filter, passing H-alpha, OIII, and H-beta. The L-eXtreme is a dual-band filter, passing only H-alpha and OIII.

    The L-eXtreme's advantage is its complete rejection of the wavelengths between the H-beta and OIII lines. This region contains no significant nebula emission but is a source of urban light pollution. By blocking it, the L-eXtreme delivers a darker sky background and higher overall contrast on most targets, making it the superior choice for maximum signal-to-noise ratio in heavy light pollution.

  • What makes the Optolong L-eXtreme different from the L-eNhance filter?

    The Optolong L-eXtreme is a dual-band filter that isolates the H-alpha and OIII emission lines. The L-eNhance is a tri-band filter that also includes H-beta. The L-eXtreme provides higher contrast and darker skies by blocking the light pollution between the H-beta and OIII lines, a region with no major nebula emissions.

    Can I use the Optolong L-eXtreme filter with my DSLR camera in the city?

    Yes, absolutely. The L-eXtreme is designed specifically for this purpose. It works exceptionally well with one-shot color cameras like DSLRs and dedicated astronomy cameras, allowing you to capture high-contrast images of emission nebulae despite heavy urban light pollution.

    How does the Optolong L-eXtreme perform on the Orion Nebula (M42) from a light-polluted suburb?

    The L-eXtreme is an excellent choice for the Orion Nebula (M42). It will dramatically darken the sky background, enhancing the faint, extended nebulosity while preserving the natural colors of the hydrogen (red) and oxygen (teal) regions. You will be able to capture significantly more detail in the nebula's structure than you could without a filter.

    Is the Optolong L-eXtreme suitable for fast telescopes like a RASA or HyperStar system?

    Yes, the L-eXtreme is well-suited for fast optical systems. Its coatings are designed to minimize the band-shift effects that can occur with steep light cones (low f-ratios), ensuring reliable performance and color balance even at f/2.

    Does the L-eXtreme filter work for monochrome cameras?

    While designed with one-shot color cameras in mind, the L-eXtreme can be used effectively with monochrome cameras. It allows you to capture H-alpha and OIII data simultaneously. For serious monochrome imaging, separate narrowband filters for Ha, OIII, and SII will offer more control, but the L-eXtreme provides a convenient way to gather data for a bicolor Hubble-palette style image in less time.

    Why doesn't the Optolong L-eXtreme pass H-beta light?

    This is a deliberate design choice to maximize contrast. While a few nebulae, like the Horsehead Nebula (Barnard 33), have a notable H-beta signal, most emission nebulae are dominated by H-alpha and OIII. By blocking the H-beta line and the region between it and OIII, the L-eXtreme eliminates more light pollution, leading to a better signal-to-noise ratio on the vast majority of targets.

  • Substrate B270
    Thickness 1.85mm
    Peak Transmission T>90%
    Blocking Range 300-1000nm
    Blocking Depth Light pollution line blocking >99%
    Surface Quality 60/40
    Transmitted Wavefront RMS λ/4
    Parallelism 30s
    Available Sizes 1.25" Mounted, 2" Mounted
  • Optolong 3-Year Warranty