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Chroma Blue Filter

Chroma Blue Filter

by Chroma
SKU CT-27043-1.25M
$150.00 - $500.00
$150.00
$150.00 - $500.00
$150.00
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  • Blue broadband filter for LRGB color imaging
  • 3.0 mm thick substrate, parfocal with other Chroma astronomy filters
  • Transmitted wavefront better than 0.25 waves/inch
  • Designed for optical systems of f/4.0 or slower
  • Durable sputtered hard coatings with a rear anti-reflection coating
  • Manufactured in Vermont, USA
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  • Description
  • FAQ
  • Specifications
  • In the Box
  • Warranty

  • Chroma Blue Filter

    The Chroma Blue Filter is built on a uniform 3.0 mm substrate to maintain focus across your LRGB set, with a transmitted wavefront better than 0.25 waves/inch to preserve the resolution of your optics. It is designed for systems at f/4.0 and slower, and its rear anti-reflection coating helps prevent ghosting. Manufactured in Vermont, USA, it provides the blue channel for star colors and the faint, scattered light of reflection nebulae.

    Isolating the Blue Channel for True-Color Imaging

    As a core component of any LRGB filter set, the Chroma Blue filter isolates the blue portion of the visible spectrum. This channel is critical for rendering accurate star colors, especially for hot, young O- and B-type stars. It is also the key to revealing the structure of reflection nebulae, such as the gas and dust surrounding the stars of the Pleiades (M45), which scatter blue light most effectively.

    3.0mm Parfocal Design with Sputtered Hard Coatings

    Every Chroma astronomy filter except the LoGlow is manufactured on a single, 3.0 mm thick substrate, so they are parfocal across a set. This means filter thickness does not change focus when you switch between your Luminance, Red, Green, and Blue filters, saving time during an imaging session. The coatings are applied via a durable sputtering process that bonds them to the glass, making them resistant to humidity and temperature changes.

    • Transmitted Wavefront (better than 0.25 waves/inch): The filter adds very little wavefront error to the image formed by your telescope.
    • Sputtered Hard Coatings: Durable sputtered hard coatings on a single substrate with no laminations. The primary coating is on the front surface, while the rear surface has an anti-reflection coating to prevent ghosting.

    Engineered for Systems f/4.0 and Slower

    Chroma designs their broadband filters for use in optical systems with a focal ratio of f/4.0 or slower. Broadband filters are less sensitive to band shift than narrowband filters, and staying in this range keeps the passbands of your LRGB set working as designed, for example with typical refractors, Schmidt-Cassegrains, or Ritchey-Chrétien telescopes.

    A wide range of sizes are available to match your imaging train, from 1.25" mounted filters typically used with smaller sensors to 50 mm unmounted filters typically used with full-frame and larger sensors. Standard mounted versions include M28.5x0.6 threads for 1.25" filters and M48x0.75 threads for 2" filters.

  • What is the primary purpose of the Chroma Blue filter in astrophotography?

    The Chroma Blue filter is used as part of an LRGB (Luminance, Red, Green, Blue) set to create full-color astronomical images. It captures the blue wavelengths of light, which are essential for rendering natural star colors and for imaging reflection nebulae and the blue spiral arms of galaxies.

    How does the Chroma Blue filter help when imaging a target like the Andromeda Galaxy (M31)?

    For a galaxy like M31, the Chroma Blue filter is critical for capturing the light from the hot, young, blue stars in the spiral arms. This data, when combined with Red and Green channels, allows you to create a natural-color portrait of the galaxy, distinguishing the active star-forming regions from the older, yellowish core.

    Why is the 3.0 mm thickness of the Chroma Blue filter a key feature?

    The standardized 3.0 mm substrate thickness ensures the Chroma Blue filter is parfocal with other Chroma astronomy filters (L, R, G, and narrowband). This means filter thickness does not change focus when you change filters in your filter wheel, which saves time during an automated imaging sequence.

    Can I use the Chroma Blue filter with my fast f/2 telescope?

    Chroma specifies that this filter is designed for systems of f/4.0 or slower. While a broadband filter is more tolerant of fast focal ratios than a narrowband one, using it at f/2 may introduce a slight shift in the bandpass. This could alter the color balance relative to the other filters in the set. For optimal color fidelity, it is best to use it within the recommended f/4.0+ range.

    What size Chroma Blue filter should I choose for a full-frame sensor camera?

    For cameras with full-frame sensors (36x24 mm), the 50 mm round or 50 x 50 mm square unmounted filters are typically needed to avoid vignetting (darkening of the corners). The 2" mounted (M48 thread) and 36 mm unmounted sizes typically suit APS-C class sensors; vignetting also depends on filter-to-sensor spacing and focal ratio.

    Are all Chroma astronomy filters parfocal with this Blue filter?

    Yes, all Chroma astronomy filters are designed to be parfocal with each other, as they share the same 3.0 mm substrate thickness. The only exception noted by Chroma is their LoGlow Light Pollution filter (part #27030), which is built on a different thickness substrate and would require refocusing.

  • Manufacturer Chroma Technology Corp (Vermont, USA)
    Chroma Part Number 27043
    Sizes Offered 1.25" mounted (threaded ring, M28.5x0.6 male), 2" mounted (M48 threaded ring, M48x0.75 male), 31 mm, 36 mm and 50 mm round unmounted, 50 x 50 mm square unmounted
    Cell Thread 1.25in M28.5x0.6 male; 2in M48x0.75 male (unmounted sizes have no cell)
    Glass Thickness 3.0 mm substrate
    Parfocal Yes, with other Chroma astronomy filters (except LoGlow 27030)
    Recommended Focal Ratio Designed for f/4.0 or slower
    Coatings Durable sputtered hard coatings on a single substrate, AR coating on rear
    Transmitted Wavefront Better than 0.25 waves/inch
    Manufacturing Location Vermont, USA
    Warranty Chroma lifetime warranty for sputtered catalog filters

    • Chroma Blue Filter

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  • Chroma Lifetime Warranty