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.
What step down adapter is suggested from a 52 mm to "-- mm"?
For adapting any cell mounted Baader 2 inch Filter onto a camera lens with 52mm front filter thread you will need:
#2408166 Baader DSLR 2" Filter-Holder M48/SP54: http://www.baader-planetarium.com/en/baader-dslr-2%22-filter-holder-m48sp54.html
#2958052 Baader Lens-Adapter-Ring SP 54/ M52: http://www.baader-planetarium.com/en/baader-hyperion-dt-ring-sp54m52-for-dtadapter-iiandiii-and-hyperion-eyepieces.html
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 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: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
|Filter mounted||Mounted (LPFC 6mm)|