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Pegasus Astro 2 inch mounted photographic filter - OIII 7nm
Pegasus Astro 2 inch mounted photographic filters, LRGB and SHO set
Pegasus Astro 2 inch mounted photographic filter - OIII 7nm
Pegasus Astro 2 inch mounted photographic filters, LRGB and SHO set

Pegasus Astro 2inch mounted photographic filter - O3 7nm

by Pegasus Astro
SKU PEG-FLTR-2M-O3
$246.00 - $246.00
$246.00
$246.00 - $246.00
$246.00
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  • Isolates the 500nm Oxygen-III emission line
  • 7nm FWHM bandpass for high-contrast imaging
  • Greater than 80% average transmission at 500nm
  • Parfocal design minimizes refocusing between filters
  • 1/4 wavefront polished 2mm thick glass
  • Standard 2-inch (M48 x 0.75) filter cell
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  • Description
  • FAQ
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  • 2-inch Mounted Photographic Filter - OIII 7nm

    This 2-inch mounted OIII filter isolates the critical 500nm oxygen-III emission line with a tight 7nm bandpass and over 80% peak transmission, ensuring maximum signal from planetary nebulae and supernova remnants. The 2mm thick glass is polished to a 1/4 wavefront standard and housed in a standard M48 x 0.75 threaded cell, making it a parfocal drop-in for any 2-inch filter wheel or drawer.

    7nm Bandpass: Isolate OIII at >80% Transmission

    The core of this filter is its 7nm Full-Width Half-Maximum (FWHM) bandpass, centered precisely on the 500nm wavelength of doubly ionized oxygen (OIII). This narrow window dramatically increases contrast by rejecting light pollution and unwanted starlight, making the faint structures of emission nebulae stand out against a dark sky background. With an average transmission greater than 80%, the filter passes maximum signal from your target, preserving precious photons for a cleaner final image.

    1/4 Wavefront Polish and Parfocal Design

    Image quality is maintained by polishing the 2mm thick optical glass substrate to a 1/4 wavefront standard, preventing any degradation of your telescope's resolution. Multilayer anti-reflection coatings eliminate halos and internal reflections around bright stars. The filter is engineered to be parfocal, meaning you won't need to make significant focus adjustments when switching between other parfocal filters, streamlining your imaging sequence and keeping your stars sharp across all channels.

    2-inch OIII 7nm vs. Tighter 3nm/5nm Filters

    Choosing a 7nm bandpass is a deliberate balance between contrast and signal strength. While tighter 3nm or 5nm filters can offer slightly higher contrast under heavily light-polluted skies, they also require longer exposure times and can be more susceptible to wavelength shift with very fast optical systems.

    • 7nm Advantage: The wider 7nm bandpass gathers more signal in a shorter time, making it ideal for imagers with less-than-perfect seeing, those using shorter total integration times, or telescopes faster than f/4 where band shift can become a factor.
    • Use Case: This filter is an excellent workhorse for a wide range of celestial targets, from the expansive Veil Nebula (NGC 6960) to the compact Dumbbell Nebula (M27), delivering strong signal-to-noise ratios without demanding exceptionally long sub-exposures.

  • What celestial objects are best for this OIII 7nm filter?

    This filter excels on emission nebulae with strong Oxygen-III signal. Prime targets include planetary nebulae like the Dumbbell Nebula (M27) and Ring Nebula (M57), and supernova remnants such as the Veil Nebula (NGC 6960) and Crab Nebula (M1). It is the primary filter for capturing the teal and blue structures within these objects.

    How does the 7nm bandpass of this OIII filter affect exposure times?

    Compared to a tighter 3nm or 5nm filter, a 7nm bandpass allows more light to reach the sensor in the same amount of time. This means you can typically achieve a strong signal with shorter sub-exposures. This is a significant advantage when imaging conditions are not perfect or when imaging time is limited.

    Is this 2-inch OIII 7nm filter parfocal with other filters?

    Yes, it is designed to be parfocal. This means that when used in a filter wheel with other parfocal filters (typically from the same manufacturer or series), your focus point should remain nearly identical. This minimizes the need to refocus after a filter change, which is crucial for automated imaging runs.

    Can I use this 2-inch OIII 7nm filter for visual observing?

    While designed for photography, this filter can be used visually on certain objects with a large aperture telescope (typically 8 inches or more). It will darken the sky significantly and may help certain planetary nebulae stand out, but the view will be very dim. A dedicated visual nebula filter with a wider bandpass is usually a better choice for non-photographic use.

    Will this OIII 7nm filter work well with my fast f/4 Newtonian telescope?

    Yes, a 7nm bandpass is often a better choice for fast optical systems (f/5 and below) than ultra-narrow 3nm filters. Fast light cones can cause a slight wavelength shift as they pass through the filter, and a 7nm bandpass is more tolerant of this effect, ensuring the OIII signal is not cut off at the edges of the field.

    What does the M48 x 0.75 thread on this filter mean for compatibility?

    The M48 x 0.75 thread is the standard for all 2-inch astronomical filters. It means this filter will thread directly into any accessory designed to accept 2-inch filters, including 2-inch filter wheels, filter drawers, and the nosepiece of many cameras and eyepieces.

  • Filter Type Narrowband OIII
    Size 2 inch (mounted)
    Bandpass (FWHM) 7nm
    Central Wavelength 500 nm
    Peak Transmission >80% (average)
    Optical Polish 1/4 wavefront
    Threads M48 x 0.75
    Parfocal Yes
    Coatings Multilayer Anti-reflection
    Glass Thickness 2mm
    Cell Thickness 5mm (filter) + 2.5mm (thread)
    Shape Round

    • 2-inch Mounted OIII 7nm Filter

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    • Protective Case

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  • Pegasus Astro 2-Year Warranty