Baader D-ERF Filter 180mm Energy Rejection Anti-IR
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Vai al moduloThe Baader D-ERF 180mm filter is an infrared pre-filter mounted in front of the telescope objective, essential for H-alpha solar observation with Solar Spectrum filters: it reduces the thermal load, protects the etalon and stabilizes the band wavelength.
What the D-ERF is for
An ERF (Energy Rejection Filter) blocks most of the solar energy before it enters the optical tube, preventing overheating of the H-alpha etalon and the telescope optics — a particularly relevant issue on SCT/Mak catadioptrics, where internal heat causes image turbulence. The result is a "cold" focus, longer H-alpha filter life, and no internal air currents in the tube.
High-precision BK7 optical glass
Unlike older red-glass ERFs, prone to internal defects, the D-ERF is made of high-quality BK7 optical glass, plane-parallel worked and polished to 1/10 wave across the entire surface.
Multi-layer dielectric coating
Energy rejection is achieved through a highly resistant multi-layer dielectric coating on both glass surfaces, which also protects the surface from scratches.
Technical specifications
| Diameter | 180 mm |
| Glass thickness | 12 mm |
| Material | BK7 optical glass |
| Coating | Multi-layer dielectric IR-Cut |
| Half-Band-Width (HBW) | 80 nm |
| Supplied as | Unmounted glass (no filter cell) |
| Made in | Germany |
Frequently asked questions
Does the D-ERF replace the H-alpha filter? No, it's a pre-filter: it must always be used together with a Solar Spectrum H-alpha filter, never alone.
Is it suitable for direct visual observation of the Sun? No: without a downstream H-alpha filter, the D-ERF alone is not safe for visual observation.
Does the filter include a mount? No, it is supplied as unmounted glass.
⚠️ Safety warning
The D-ERF must always be mounted in front of the telescope aperture and used exclusively together with a Solar Spectrum H-alpha filter. Improper use can cause severe, permanent eye damage.