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Daystar Energy Rejection Filter for Refractor - 80-150mm ERF Glass

Daystar Energy Rejection Filter for Refractor - 80-150mm ERF Glass

by Daystar Filters
SKU DAY-E-120N80
CA$770.00 - CA$2,303.00
CA$770.00
CA$770.00 - CA$2,303.00
CA$770.00
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  • Full-aperture solar energy rejection filter for refractors
  • Available in 80mm, 100mm, 130mm, and 150mm clear apertures
  • Rejects harmful UV and IR radiation to protect your downstream filter
  • Acts as an aperture mask to achieve the f/30 focal ratio required by Daystar filters
  • Custom-machined aluminum cell for a precise fit on your telescope's dew shield
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  • Description
  • FAQ
  • Specifications
  • In the Box
  • Warranty

  • Daystar Energy Rejection Filter for Refractor - 80-150mm ERF Glass

    The Daystar Energy Rejection Filter (ERF) is the essential first component for safe, high-resolution solar observation, available in apertures from 80mm to 150mm. This front-mounted filter protects your entire optical system by rejecting damaging UV and infrared energy before it enters your telescope. By managing the heat load and acting as a precise aperture mask, the ERF ensures your Daystar Quark or other filter assembly receives a light cone at the required f/30 focal ratio for optimal contrast and uniformity.

    Thermal Protection: Rejecting UV/IR Heat Before the Etalon

    A telescope is a light bucket, and when pointed at the sun, it also becomes a heat collector. The Daystar ERF is a specialized dielectric coated or colored glass filter that transmits the desired visible wavelengths while reflecting or absorbing concentrated ultraviolet and infrared radiation. Placing this protection at the front of your refractor prevents a dangerous buildup of heat inside the optical tube, safeguarding your expensive etalon and other internal components from thermal stress and potential damage.

    Achieving the Critical f/30 Focal Ratio

    Daystar's sub-angstrom filter assemblies demand a highly collimated beam of light to function correctly, operating best at a focal ratio of f/30 or slower. The ERF serves a dual purpose by also acting as an aperture mask, stopping down your telescope's faster native focal ratio to this required value. This ensures the light entering the etalon is at a straight angle of incidence, which is critical for achieving a uniform, high-contrast image of the solar chromosphere across the entire field of view.

    Custom-Machined for a Secure Fit on Your Refractor

    An ERF must be securely mounted to the front of your telescope with no risk of slipping. Each Daystar ERF is housed in a custom-machined aluminum cell and cap assembly, built to order based on your specific telescope. To ensure a perfect fit, you must provide the precise outside diameter of your refractor's dew shield at the time of order. This made-to-order approach guarantees a safe, stable platform for your solar observing sessions.

  • What is the primary purpose of the Daystar ERF for refractors?

    The Daystar ERF has two main functions. First, it acts as a pre-filter, rejecting harmful and heat-inducing Ultraviolet (UV) and Infrared (IR) light before it enters the telescope. Second, it serves as an aperture mask to slow your telescope's optical system to the f/30 focal ratio required for optimal performance with Daystar's H-alpha filter systems like the Quark.

    Why is an f/30 focal ratio required for the Daystar ERF and Quark filters?

    The Fabry-Pérot etalon inside a Daystar filter is extremely sensitive to the angle of incoming light. An f/30 light cone is highly collimated (the light rays are nearly parallel), which allows the etalon to maintain its narrow bandpass uniformly across the entire field of view. Using a faster focal ratio would result in a significant loss of contrast and detail in solar features like filaments and prominences.

    How do I determine the correct size Daystar ERF for my telescope?

    You need to provide the exact outside diameter of your telescope's dew shield, measured with a ruler or calipers. Daystar will custom-machine the filter cell for a snug, secure fit based on this measurement. Failing to provide an accurate measurement will delay your order. You should also choose an ERF glass size appropriate for your desired aperture; for high-resolution imaging, a larger ERF is generally preferred.

    Can I use a Daystar ERF with a telescope larger than 150mm?

    While these specific ERF models go up to 150mm, Daystar does make larger custom filters. However, for apertures above 150mm, heat management becomes a significant engineering challenge. The ERF serves to stop down the aperture to create the f/30 beam, so a 150mm ERF can be used on a larger telescope, but it will limit the working aperture to 150mm.

    Will the 100mm Daystar ERF work for imaging prominences on my 120mm f/7 refractor?

    Yes, it will work perfectly. The 100mm ERF will act as an aperture mask, effectively turning your 120mm f/7 telescope into a 100mm f/8.4 system (840mm / 100mm). You would then use a Barlow lens to bring the final focal ratio to f/30 or slower. The 100mm aperture is excellent for capturing detailed views of both surface granulation and prominences.

    What happens if I don't provide my dew shield measurement when ordering the Daystar ERF?

    Your order will be placed on hold. These filters are custom-machined on a per-order basis, and production cannot begin without the precise outside diameter of your telescope's dew shield. Providing this measurement in your order notes is critical to avoid delays.

  • Filter Type Front-mounted Energy Rejection Filter (ERF) for solar observing
    Telescope Compatibility Refractors
    Available Configurations 80mm ERF Glass | Cell | 110mm ID Cap
    80mm ERF Glass | Cell | 120mm ID Cap
    100mm ERF Glass | Cell | 120mm ID Cap
    100mm ERF Glass | Cell | 130mm ID Cap
    100mm ERF Glass | Cell | 140mm ID Cap
    100mm ERF Glass | Cell | 150mm ID Cap
    130mm ERF Glass | Cell | 150mm ID Cap
    130mm ERF Glass | Cell | 160mm ID Cap
    130mm ERF Glass | Cell | 170mm ID Cap
    130mm ERF Glass | Cell | 180mm ID Cap
    130mm ERF Glass | Cell | 190mm ID Cap
    150mm ERF Glass | Cell | 180mm ID Cap
    150mm ERF Glass | Cell | 190mm ID Cap
    150mm ERF Glass | Cell | 200mm ID Cap
    150mm ERF Glass | Cell | 210mm ID Cap
    150mm ERF Glass | Cell | 220mm ID Cap
    Required Focal Ratio Optimized for use in an f/30 or slower light cone
  • Daystar Filters Warranty