DayStar Energy Rejection Filter

Block Heat, Protect Optics, Capture Sharper Solar Images

The DayStar Energy Rejection Filter keeps your telescope cool by blocking harmful UV & IR light. This ensures crisp, high-contrast H-alpha views—without risking damage to your optics.

Features

• Protects Optics from Heat Damage: Absorbs unwanted infrared and ultraviolet light, preserving your filter’s performance.
• Optimized for f/30 Performance: Creates the ideal light path for sharp, high-resolution solar imaging.
• Custom Machined for a Precise Fit: Precision-cut to match your telescope’s exact dew shield size.
• Enhances Contrast & Detail: Reduces heat distortion and improves visibility of solar features.
• Ensures Correct Light Entry: Aperture-masked design maintains proper light angle for sharper images.

Why Choose the DayStar ERF?

Solar astronomy requires precision, and every component in your setup matters. Without proper protection, excessive heat can degrade your optics, distort images, and shorten the lifespan of your filters.

The DayStar Energy Rejection Filter protects your telescope from heat damage, ensuring a more stable optical system. The result? Sharper, high-contrast solar images.

Every DayStar ERF is custom-machined for a seamless installation, ensuring peak performance. It also acts as an aperture mask, aligning light at the correct angle to help achieve the f/30 configuration needed for high-resolution solar imaging.

Why Does f/30 Matter for Solar Observing?

For the best H-alpha solar imaging results, your telescope’s optical system should operate at f/30 or slower. This extended focal ratio:

• Reduces off-band light contamination, improving contrast and revealing fine solar details.
• Helps H-alpha etalon filters perform at their best by maintaining the correct angle of incidence for incoming light.

Many modern telescopes have shorter focal ratios (e.g., f/7 to f/10), which means they must be adjusted to reach f/30. If your telescope has a shorter focal ratio, you may need to use a Barlow lens to extend the focal length and achieve the best performance.

• Refractors (f/6 - f/8): Typically need a 4x - 5x Barlow to reach f/30.
• Schmidt-Cassegrain & Maksutov (f/10 - f/15): May need a 2x - 3x Barlow for optimal results.
• Larger aperture telescopes: Benefit from a Barlow lens to maintain contrast and improve etalon performance.

What’s the ERF Made Of?

The DayStar Energy Rejection Filter is constructed from high-quality optical glass and features advanced coatings to selectively block infrared (IR) and ultraviolet (UV) light while transmitting visible wavelengths used for solar observation.

Depending on the specific telescope and filter configuration, ERFs may be:

• Red or Yellow Glass – Absorbs unwanted wavelengths and enhances contrast in H-alpha imaging.
• Dielectric-Coated Optical Glass – Reflects IR and UV light while allowing the desired solar wavelengths to pass through, reducing heat buildup inside the telescope.

These coatings ensure your optics stay cool, improve image contrast, and extend the life of your solar filters.

How to Order Your Custom ERF

Each DayStar Energy Rejection Filter is custom-machined to fit your telescope’s exact specifications. After placing your order, please email us at orders@astrotelescopium.com with:

• Your order number
• Your telescope's brand and model
• The outside diameter of your telescope’s dew shield (measured with a ruler at the very front of the telescope)

Important: Your order will be put on hold until we receive this measurement. Providing an accurate measurement ensures a secure, perfect fit. No modifications needed—just a seamless installation tailored to your telescope.