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

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

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€ 295.00 Price excl. German VAT tax (19%): € 247.90

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  • 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
  • Half-Band-Width (HBW): 80 mm – see also graph
  • Filter WITHOUT cell – 3D-printed filter cells - customized for your telescope, can be ordered in addition (not available as standalone product)

Important Note: Please note our information on the availability of 3D-printed or CNC-turned cell mounts for front side D-ERF filters as custom-made products.

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€ 295.00 Price excl. German VAT tax (19%): € 247.90

Product Questions

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What's 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)
What are the threads and pitch of your 1.25" and 2" filters?
Question by: Anders G. on Sep 20, 2017 12:55:00 PM | 1 Answer(s)
Is it possible to use a cheaper ERF (energy rejection filter) from another manufacturer or dealer for the SolarSpectrum H-Alpha filters than the D-ERF?
Question by: Johannes H. on Jan 18, 2017 10:37:00 AM | 1 Answer(s)
Is possible use the d-erf with my telescope celestron 127slt?
Question by: Cristian on Aug 17, 2021 8:19:00 AM | 1 Answer(s)
Is it possible to order a DERF + suitable frame that would work on a Celestron 8" SCT? The DERF is available as 180 mm, not 200 mm, but could you build a frame that fits an 8" and use a 180 mm DERF together with a Solar Spectrum?
Question by: Ben Kalland on Feb 26, 2022 10:57:00 PM | 1 Answer(s)
What is the irradiance damage threshold for the solar spectrum at sea level irradiance of your filters? 2x, 3x, 4x? Likewise, what are the temperature ranges for performance and survival?
Question by: Mark J Christensen on Jun 26, 2021 7:41:00 PM | 1 Answer(s)
Regarding the ERF filters, what is the true (actual) diameter of the filters? Is it exactly 180 mm? Or is there an excess edge for a cell to hold onto?
Question by: Arnaud van Kranenburg on Apr 24, 2022 1:15:00 PM | 1 Answer(s)
I'm going to buy one for my Takahashi FS-152 doublet fluorite refractor with Daystar Quark. Which size should I choose? Will it fit my scope objective or do I need anything else? Thanks.
Question by: Howard Gao on Jul 6, 2017 10:57:00 AM | 1 Answer(s)
How can I tell which side is which on an older erf filter I have. I cannot tell which side is gold or blue. I CAN tell that one side is more reflective on its front surface giving a crisper reflection than the other side. Should that side face the sun??
Question by: Ed Henry on Oct 4, 2021 4:48:00 PM | 1 Answer(s)
Where can I find/download a full specifications with also thickness of each etc.?

Thank you
Question by: Mauro on Feb 8, 2019 3:43:00 PM | 1 Answer(s)
Is it possible to use your Sundancer II with my 8" Edge? - Do you make a suitable ERF that I could use to allow me to use my 8" Edge? Thank you.
Question by: Jean M Dean on Feb 21, 2022 1:46:00 PM | 1 Answer(s)
I have successfully used for many years the D-ERF as a front mounted ERF with various PST Mod.
Concern has been raised about the NIR-IR transmission.
What is the transmission from 1500 to 2500A?
Would using a KG3 filter in parallel be beneficial.
Question by: Ken Harrison on Sep 29, 2019 6:52:00 AM | 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 80 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 80nm-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:

Baader D-ERF Energy Rejection filters are intended for use only as a Pre-Filter for Solar Spectrum H-Alpha filters. The D-ERF filter must always be present and mounted ahead of the telescope objective. The filter should be oriented with the primary coated face towards the sun (an arrow mark on the rim of the filter points toward this side). The D-ERF filter must be used together with the Solar Spectrum H-Alpha filter. Irreparable eye damage will result if the D-ERF is used by itself for visual observation

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4 Item(s)

McSlama 355/12/2021 22/12/202111:58
  • Rating:
Sicherheit durch D-ERF
Der Filter schützt jetzt das optische Gerät, ein RedCat51, und meine Augen bei Langzeitbeobachtungen, auch wenn die Öffnung nur 51mm hat. Ohne Fassung musste ich ihn jetzt mit 2 cm breiten Moosgummi-Ringen in die Tauschutzkappe eigeklemmen und er passt perfekt.
  • Er passt
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Ewan 92/04/2021 03/04/202117:31
  • Rating:
Solar Work
I wanted THE best images i could possibly achieve with my setup.
I went with a Baader D-ERF 135mm to pair with my Daystar Quark Chromosphere & 152mm F5.9 Tecnosky Achromat.
The CLEAR aperture of the D-ERF is 125mm, with the 152mm + Quark it gives a final F Ratio of F30...exactly what the Quark likes for the best possible images.
The D-ERF fits very well, is secure through the day & is not too much additional weight. I usually track the sun for 4-7 hours straight through the summer months knowing my instruments are protected as best as possible.
  • Protects my equipment from damage.
  • Nothing (cheaper would be nice but you pay for quality)
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Timo I 216/08/2020 04/08/202016:33
  • Rating:
Baader D-ERF filter with 152/1200 apochromatic refractor
Full sized (160mm) Baader D-ERF filter provides several choices for my visual/imaging solar Ha system with a Daystar Quark Combo unit. With scope's full aperture (150mm) this D-ERF mask can be used with 4x barlow (=150/4800mm setup, F/32). In more limited seeing conditions I can use aperture mask of 100mm together with a 2.5x barlow (=100/3000mm setup, F/30). And by limiting scope's aperture even further (=75/2400mm, F/32 system) a 2x barlow can be used.

Baader D-ERF seems to be worth every euro spent there, because I could get a contrasty and detailed Ha-view with above described 3000mm focal length setup tested today (despite of some high altitude clouds moving around!). Minor minus for this quality filter comes from the missing commercial frame options available from Baader for this filter type. Anyway, my ATM DIY frame solution for this D-ERF filter placement can be seen in the attached images.
I'm looking forward to get more excellent results with this Ha system.
  • Optical quality does not disappoint! Bonus: a full aperture D-ERF filter keeps heat out of my refractor tube internals.
  • Pricey solution, but well worth the cost considering the versatility it gives me as a side effect.
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Enrico 44/02/2019 14/02/201919:09
  • Rating:
Hochwertiger Energieschutzfilter
Habe mir diesen hochwertigen D-ERF Filter für den Umbau zugelegt. Bringt ein zuverlässiges solides Bild. Keine Geisterbilder etc. . Visuell auch ein Genuss mit DER Sicherheit für die Augen!!!
  • Hochwertig zuverlässig
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