Skip to content

DayStar 80mm Off-Axis ERF with 281mm Inside Diameter Cap

by DayStar
SKU E-281F80
Original price $550.00 - Original price $550.00
Original price
$550.00 - $550.00
Current price $550.00
In stock

Ships To: United States & Canada 🇺🇸 🇨🇦

✓ Free U.S. Shipping (on most orders over $150 USD)

✓ Price Match Available

✓ Authorized Dealer

✓ Bulk Order Discounts Available

✓ Questions? Call Us 1-800-860-3429

Ships In: 1-3 Business Days

Estimated Delivery Time: 3-7 Business Days

Shipping & Returns

We offer Free Shipping across the United States (Lower 48 States) on most orders over $100 USD.

Shipping fees will apply on most orders shipping across Canada, with some exceptions.

We also offer a 30 Day Return Policy on most of the products that we carry. Some limitations may apply.

For full details on our Shipping & Returns Policy, please click here.


The vast majority of products that we sell, with a few exceptions, are covered under Warranty.

To view the Warranty details for each brand that we sell, including products that do not qualify for Warranty, please visit here.

DayStar 80mm Off-Axis Energy Rejection Filter with 281mm Inside Diameter Cap - for 9.25-inch SCT - E-281F80

The DayStar 80mm Off-Axis ERF with 281 Inside Diameter Cap for 9.25-inch SCT is designed to enhance the performance of your telescope.

Energy Rejection Filters (ERFs) play a crucial role in minimizing heat buildup on the filter assembly.

They work by either absorbing or reflecting UV and/or I light while allowing light in the desired visual spectrum to pass through.

These filters may appear in Red or Yellow glass or utilize dielectric materials to filter out IR and UV, while still transmitting the desired visual spectrum.

Additionally, the ERF can function as an aperture mask, ensuring that light enters the filter at a straight angle of incidence.

For optimal performance, DayStar filter assemblies are most effective when used at f/30 or slower configurations.

Achieving this can be easily accomplished with the appropriate ERF and/or Barlow lens.

This ensures that your telescope operates at its best, providing clear and detailed observations of celestial objects.

 Important Instructions:

To facilitate a seamless integration, after your order is placed, please reach out to us via email with the following details:

  • Please indicate the telescope designated for use with this ERF and accurately measure the outer diameter of its dew shield at the front using a ruler. This precise dimension is crucial, as each ERF is custom made to guarantee a flawless fit. 
  • If this measurement is not provided, there may be a temporary delay in processing your order until the required information is obtained. Your satisfaction and optimal performance is our priority.


    Features & Highlights:

    • 80mm ERF Glass: Crafted with precision, the 80mm aperture of the ERF is expertly tailored for solar observation. Striking a harmonious balance between light-gathering capacity and resolution, it delivers crystal-clear, detailed views of solar phenomena.
    • 281mm Inside Diameter Cap: Included with the package, the 281mm inside diameter cap ensures a secure, snug fit with compatible telescopes. This cap plays a crucial role in minimizing stray light, enabling precise and unobstructed solar observations.
    • SCT Compatibility: Engineered specifically for 9.25-inch SCT (Schmidt-Cassegrain) telescopes, the ERF seamlessly integrates with your existing optical setup. This ensures a seamless, hassle-free solar observation experience.
    • Advanced Energy Rejection: Designed to substantially reduce heat load on your filter assembly, the ERF efficiently absorbs or reflects UV and/or Infrared light. This enables the transmission of light within the desired visual spectrum.
    • Multi-Coated Optics: All optical surfaces undergo precision multi-coating to enhance light transmission and diminish internal reflections. The result is vivid, high-contrast solar imagery with exceptional clarity and detail.
    • Off-Axis Design: The off-axis design grants an unimpeded view of the solar disk, maximizing the amount of light captured by the telescope. This feature ensures meticulous observation of the sun's features.
    • Dual Functionality as an Aperture Mask: The ERF serves a dual purpose as an aperture mask, guaranteeing a direct angle of incidence for incoming light. This unique feature bolsters filtering efficiency, ensuring that only the desired wavelengths are transmitted.
    • Robust Construction: Fashioned from top-tier materials, the ERF assures durability and longevity. It is engineered to withstand the demands of outdoor use while maintaining peak performance over time.
    • Recommendations for Optimal Performance: For optimal results, DayStar suggests operating filter assemblies at f/30 or slower. This configuration is easily achieved with the appropriate ERF and/or Barlow. In cases of higher resolution or larger aperture configurations, incorporating a Barlow is advised for an enhanced viewing experience.


          What's Included:

          ✓ DayStar 80mm Off-Axis ERF for 9.25-inch SCT

           ✓ 5 Year Warranty



          SKU E-281F80
          Block Ultraviolet Yes
          Block Infrared Yes

          Customer Reviews

          Be the first to write a review