Baader D-ERF Energy Rejection Filter (75 - 180mm)

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Baader D-ERF Energy Rejection Filter (75 - 180mm)
Starting at: € 275.00 Price excl. German VAT tax (19%): € 231.09
  • D-ERF (Dielectric Energy Reflection Filter) in different sizes
  • Pre-filter to reduce heat during H-alpha observation with SolarSpectrum Filters
  • Plane parrallel plate (without filter cell) with IR-Cut dielectric coating
  • non-ageing sealed coating edges
Important note: D-ERF Filter are specially made on request and not available for sale online. We only deliver them together with a purchase of Solar Spectrum H-alpha Filters. Please ask us for an offer

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Starting at: € 275.00 Price excl. German VAT tax (19%): € 231.09

Product Questions

Whats the actual size of your 2" filters in "mm" with and without frame/ring?
What step down adapter is suggested from a 52 mm to "-- mm"?
Question by: Waqas Ahmad on Oct 10, 2016 7:54:00 PM | 1 Answer(s)


D-ERF Testreview from Christian Viladrich Dear Baader Planetarium, I have my D-ERF 160mm tested on the interferometric bench of AiryLab. Best regards, Christian Viladrich

D-ERF Energy Rejection Filter

D-ERF heat prefilter for H-alpha observation with surface filtering in the Solar Spectrum and Prominances (with IR-block coating)

Our "GREAT" D-ERF Energy Rejection Filters are unique in the world - made in Germany!
D-ERF Prefilter
D-ERF Prefilter Heat Reduction

Our 43-layer dielectric DWDM-coating delivers a COOL-beam of pure red light, with a HBW of 45 nm! The glass substrate in this case is no longer any kind of soft and streaky colored absorption glass, but clear BK7 of the highest homogeneity, fine-optically polished to the quality grade of the objective-lens surfaces, and with all the reflection performance coatings on one side. This reflects all the unwanted spectrum from 280 nm up to 1500 nm, while leaving open just that 45nm-wide spectral window around H-alpha. It is hellishly difficult to design such a performance coating, as well as the counterside anti-reflection multicoating, in such a way that no coating-induced stress builds up inside the glass substrate. If these coatings systems on either side of the plate are not done exactly right, to cancel out the stresses induced by the coating layers, the plane-parallel surfaces may easily be distorted, meaning the 1/10 wave flat plate deforms into an irregular curved substrate that acts as a (bad) lens. Our D-ERF filter-layers are designed with the utmost care, applied with the world‘s most advanced optical coating machines, and the final filters are all inspected and passed in autocollimation on our Carl Zeiss optical bench.

This level of care retains the full-aperture resolving power of the telescope lens while dramatically reducing the thermal energy that goes through the telescope to the Solar Spectrum filter. This not only is the main reason for a dramatic reduction of heat stress within the telescope, but also greatly reduces the thermally-induced seeing effects as well.

Important Note:

D-ERF Energy filters are PREFILTER and ONLY for use with Solar Spectrum H-alpha filter surface (and Protuberanzenansätzen) suitable. These filters are ALWAYS ON to mount the light inlet opening. The installation position toward the sun (mark on the rim of the filter) is observed. When using white-light observations of the solar surface WITHOUT light attenuation filter your eyes irreparable damage.


Additional Information

Manufacturer Baader Planetarium
SKU (#) derf-filter
Filter mounted Mounted (LPFC 6mm)

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