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

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

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Application Application Application Application Application Application Application Application Application: taken with AP 175WDFS f/8, Baader D-ERF Filter + Solar Spectrum Research Grade RG32, Baader TZ-4 and M68 Tele-Compendium, © Kai von Schauroth Application: taken with TEC 140 APO ED on 10micron GM2000 HPS II, with Baader D-ERF Energy Rejection Filter + Solar Spectrum Observer Series 1.5 - 0.5A°, Baader TZ-4 and Baader Steeldrive II, © Rüdiger Proske Application: Korona Edge taken with TEC 140 APO ED on 10micron GM2000 HPS II, with Baader D-ERF Energy Rejection Filter + Solar Spectrum Observer Series 1.5 - 0.5A°, Baader TZ-4 and Baader Steeldrive II, © Rüdiger Proske Application: taken with TEC 140 APO ED on 10micron GM2000 HPS II, with Baader D-ERF Energy Rejection Filter + Solar Spectrum Observer Series 1.5 - 0.5A°, Baader TZ-4 and Baader Steeldrive II, © Rüdiger Proske

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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.

*Filter size:

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

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Product Questions

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"?

172

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)

Our 1.25" filters have a M28.5 male (and M28.5 front female) thread / our 2" filters have a M48 male (and M48 front female) thread

Both thread sizes come with our proprietary pitch - which is not the same for the female and male threads.
This is our own proprietary "emergency solution" for uniting a world were manufacturers all over the world copy from each other - to the point that there are almost a dozen different pitches in use for male and female threads. Traditionally US-companies used to do a UNF-based pitch and the rest of the world went for metric threads - but these do vary from 0.5 to 0.75.

For this reason it does not make sense to publish our non standard pitch because our pitch is made to cope with all existing metric and US-pitch standards - and as said - our solution has evolved from sheer necessity. It is a mixture of a queer pitch and under-/over-dimensioning . We will not want to declare this as a standard and get bashed up for it. It works for us and is a result of 20 years adaptation to fit our filters onto all crazy threads we have seen. And inspite of this - every now and then there comes another "dragonboat-eyepiece" were even our filters may not fit...

Answer by: Baader Web Team (Admin) on Sep 22, 2017 1:43:00 PM

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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)

We absolutely must point out that an ERF from another dealer may void the warranty of the SolarSpectrum H-alpha Filter, so that repairs may be payable even during the warranty period.

You can buy cheaper standard ERFs, but they don't meet the same specifications as our D-ERF. Simple energy rejection filters are made of red dyed glass (Schott RG 610 or Schott RG 630). These are long pass filters which let all energy beyond ca. 570nm pass - this includes the full near infrared spectrum (heat radiation) above 630nm.

The heat at the focal point behind such an ERF filter is three times higher than behind one of our D-ERFs. This way, the immersion oil in the stack of block-, polarization and Etalon-filters will boil away. An H-Alpha-filter which is permanently overheated this way will age very fast. We can not cover this with our 5-year-warranty.

By the way: The coloured glass of these simple ERFs is rather "soft" and chemically unstable, so it can degrade over the years. The soft glass melt tends to form streaks. If they are not coated simple ERF-filters will age because of the oxygene in our atmosphere, and after some years the surface will get rough, and contrast is lost. When we were still using this glass, we had to check each and every filter on our optical bench, and many filters failed the double pass test.

The problem with the glass quality of an RG 610 remains even when it is coated with an UV/IR-reducing coating. We tried this, too, with our C-ERF (Cool ERF), but we abandoned it after some years. The soft glass often got warped during the coating procedure, so that even less filters were useful after being coated. Our experiences with this combination lead to the development of the D-ERF (Dielectrical ERF).

There are dealers and manufacturers who still offer such ERF or C-ERF filters but do not test them as thoroughly on an optical bench as we did. This is the reason why there are many cheaper C-ERFs and ERFs on the market - but the customer will pay for the cheaper costs a much higher price: a reduced image quality and a reduced lifespan of the H-Alpha filter, compared to a high-quality D-ERF.

Our D-ERF filters are made of very homogeneous, fine-polished BK-7-glass without streaks. They are coated with great effort with a dielectrical coating system which is age-resistant and fine-tuned for the Solar Spectrum filters.

A Solar Spectrum filter will outplay all its benefits (resistance to aging, sharpness and contrast) only in combination with a D-ERF, and only with this combination can we guarantee its resistance to aging. Especially a Research Grade Filter requires a good D-ERF. Every chain is only as strong as its weakest link.

Answer by: Baader Web Team (Admin) on Jan 23, 2017 10:39:00 AM

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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??

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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
M

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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.

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Question by: Jean M Dean on Feb 21, 2022 1:46:00 PM | 1 Answer(s)

This is tricky - the largest D-ERF has got 180mm, while the C8 has got an aperture of 200mm. You could use the telescope with ca. 18cm diameter, but the telescope has got a central obstruction of 6.9cm. So, the obstruction would increase from 34% to almost 40% (or a little bit more, because the D-ERF needs to be put in a frame). This means less contrast, which becomes a problem especially for visual use.

To be honest: Instead of charging you more than 2200 Euro for a D-ERF plus filter frame to turn your C8 into a telescope with less than 7" of aperture, we'd recommend to take a look at our 8" Triband telescope #2301002, which also has got special heat shields and wouldn't suffer from an increased obstruction. It is more expensive than the 180mm-D-ERF, but the improvement in image quality is worth the money.

Moving the D-ERF off-center is also no solution, as then the obstruction moves off-center, too, which has got some "interesting" optical effects – we wouldn't recommend it. It's a bit like observing with a Scheiner- or Bahtinov-mask in front of the telescope.

The third option would be mounting the D-ERF completely off-center, which would give you no more than 63mm of free aperture, so a 75mm D-ERF would be sufficient. Also note that in this case, the telescope's visual back (or the focuser) must be tilted by ca. 3 degree to point at that part of the secondary mirror where the light of the reduced aperture hits it – you would use only one half of the telescope, so the mechanics need to be adapted.
The second problem of this setup: You would turn your EdgeHD into a 63/2000 f/32 telescope at best, which is expanded by the SunDancer telecentric to 63/6000 f/95. A 40mm-eyepiece will give you a minimum magnification of 150x with an exit pupil of 0.4mm. So, that's already beyond the highest useful magnification of that aperture, and 150x is rarely useful at daytime. If you are down to the more realistic aperture of 63mm mentioned above, you're way beyond the useful magnification.
Of course, you can then add the SolarSpectrum Research Grade H-alpha 0.4x Telekompressor 2" # 2459260 to get back to 2400mm focal length... but it would be much more economic to get a cheap 80mm-telescope with about f/10 and a good focuser. Then you don't need a D-ERF and can reach lower magnifications.

Answer by: Baader Web Team (Admin) on Feb 22, 2022 9:10:00 AM

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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.

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Question by: Ken Harrison on Sep 29, 2019 6:52:00 AM | 1 Answer(s)

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D-ERF Testreview from Christian Viladrich Dear Baader Planetarium, I have my D-ERF 160mm tested on the interferometric bench of AiryLab. http://www.astrosurf.com/viladrich/astro/instrument/HASO/mesure-DERF160mm.png 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 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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Specifications