Skip to content
Optolong L-Ultimate Ha/OIII 3nm Filter
Optolong L-Ultimate Ha/OIII 3nm Filter

Optolong L-Ultimate Ha/OIII 3nm Filter

by Optolong
SKU OPT-11601
CA$404.00 - CA$545.00
CA$404.00
CA$404.00 - CA$545.00
CA$404.00
Price Match Policy!
  • Dual 3nm bandpass isolates Hydrogen-alpha and Oxygen-III emission lines
  • Blocks light pollution across the 300-1000nm spectrum
  • Greater than OD4 blocking of unwanted wavelengths
  • λ/4 transmitted wavefront for sharp, high-resolution images
  • Precision 60/40 surface quality optical glass substrate
4 in stock
Qualifies for FREE Shipping in Canada on orders over $500.
  • Description
  • FAQ
  • Specifications
  • In the Box
  • Warranty

  • Optolong L-Ultimate Ha/OIII 3nm Filter

    The Optolong L-Ultimate Ha/OIII 3nm Filter isolates critical nebula emission lines with an extremely narrow 3nm full width at half maximum (FWHM) for both its H-alpha and OIII channels. This filter achieves its deep-sky contrast by implementing greater than OD4 blocking across a wide 300-1000nm range, effectively eliminating light pollution from urban and suburban skies. Each filter is manufactured to a λ/4 transmitted wavefront standard, ensuring that the filter itself does not degrade the resolution of your optical system.

    Dual 3nm Bandpass for Maximum Nebula Contrast

    By restricting the incoming light to only the H-alpha (656nm) and OIII (500nm) emission lines within a tight 3nm window, the L-Ultimate filter dramatically increases the signal-to-noise ratio of emission nebulae. This surgical isolation means that the faint, intricate structures within targets like the Squid Nebula (OU4) or supernova remnants are captured with stark contrast against a near-black sky background. The result is an image with significantly more "pop" and detail compared to what is possible with broader-band filters.

    >OD4 Blocking for Urban Imaging

    For astrophotographers working under light-polluted skies, the L-Ultimate's primary function is its aggressive rejection of unwanted artificial and natural light. With a blocking efficiency rated at an optical density greater than 4 (>OD4), it effectively nullifies the glow from mercury vapor, high and low-pressure sodium streetlights, and the natural atmospheric airglow. This level of suppression allows you to capture clean, long-exposure data from even the most challenging urban environments, turning previously unfruitful nights into productive imaging sessions.

    λ/4 Optics and Advanced Ion Coatings

    Optolong builds the L-Ultimate filter on an optical glass substrate polished to a 60/40 surface quality and a transmitted wavefront of λ/4, preserving the sharpness of your telescope's optics. The filter's dielectric coatings are applied using an advanced ion-assisted deposition process, which creates a durable, scratch-resistant surface. This modern coating technique also ensures the central wavelength of the bandpass remains stable and does not drift with temperature changes, providing consistent results from night to night.

    L-Ultimate vs. L-eXtreme & L-eNhance: Why 3nm Matters

    While filters like the Optolong L-eXtreme and L-eNhance are effective dual-band filters, the L-Ultimate distinguishes itself with its much narrower 3nm bandpasses. This tighter specification provides several key advantages for specific imaging goals.

    • Darker Sky Background: The 3nm window passes less of the skyglow continuum and blocks more of the light from stars, leading to a darker overall background and enhanced nebula contrast.
    • Better Star Suppression: By collecting less stellar light outside the core emission lines, stars appear smaller and less prominent, allowing the faint nebulosity to dominate the image.
    • Trade-Off: The primary limitation is that its tight bandpass is not well-suited for very fast optical systems (typically f/4 and faster), where significant band-shift can occur. For these systems, a broader filter like the L-eXtreme may be more appropriate.

  • What is the main difference between the Optolong L-Ultimate and the L-eXtreme filter?

    The primary difference is the bandpass width. The L-Ultimate uses a very narrow 3nm bandpass for both H-alpha and OIII, while the L-eXtreme uses a wider 7nm bandpass. The L-Ultimate's 3nm design provides a darker sky background and better star control, maximizing contrast on emission nebulae, but it is less suited for very fast telescopes.

    Can I use the Optolong L-Ultimate filter with a DSLR or a color astronomy camera?

    Yes, the L-Ultimate is specifically designed for use with one-shot color cameras like DSLRs and dedicated color CMOS/CCD cameras. It passes both the red H-alpha and blue-green OIII light simultaneously, allowing you to capture a detailed, color-rich image of emission nebulae in a single set of exposures.

    Why is the Optolong L-Ultimate not recommended for fast telescopes (f/4 and faster)?

    Extremely narrow filters like the L-Ultimate can experience "band-shift" when used with fast optical systems. The steep light cone from a fast telescope causes the filter's central wavelength to shift away from the intended emission line for off-axis light rays. This can result in a loss of signal. For telescopes f/4 or faster, a filter with a slightly wider bandpass, like 7nm, is often a better choice to avoid this effect.

    How will the Optolong L-Ultimate perform on a target like the Veil Nebula (NGC 6960) from a city?

    The L-Ultimate is ideal for this scenario. The Veil Nebula is rich in both H-alpha and OIII, and the filter's dual 3nm bandpasses will isolate this signal while its >OD4 blocking rejects the city light pollution. You can expect to capture the delicate, filamentary structure of the nebula with high contrast against a dark background, even from a heavily light-polluted site.

    Is the Optolong L-Ultimate a good choice for my 8" f/10 SCT?

    Yes, an f/10 Schmidt-Cassegrain Telescope is an excellent match for the L-Ultimate filter. Slower optical systems like SCTs do not cause the band-shift issues seen in fast refractors or Newtonians. The filter will work at its peak efficiency, delivering maximum contrast and light pollution suppression for imaging emission nebulae.

    Does the Optolong L-Ultimate filter work on galaxies or reflection nebulae?

    No, this filter is not designed for broadband targets. Galaxies like Andromeda (M31) and reflection nebulae like the Pleiades (M45) shine by reflecting starlight across the entire visible spectrum. The L-Ultimate blocks almost all of this light, so these objects would be rendered extremely faint or invisible. It is exclusively for emission nebulae that glow at the specific H-alpha and OIII wavelengths.

  • FWHM OIII 3nm, H-alpha 3nm
    Substrate Optical Glass
    Blocking Range 300-1000nm
    Blocking Efficiency >OD4
    Transmitted Wavefront RMS λ/4
    Surface Quality 60/40
    Parallelism 30 arcseconds
    Available Sizes 1.25" Mounted, 2" Mounted

    • Optolong L-Ultimate Ha/OIII 3nm Filter with Protective Case

      × 1

  • Optolong 3-Year Warranty