Baaders D-ERF filters are exceptional solar energy rejection filters that are made in Germany

Made from plane parallel circular disks, both surfaces are precision optically polished to 1/10 Lambda. Typically, common absorbative glass type ERF filters are only 1/4~1/5 Lambda which can have a detrimental effect on the optical quality of the system, not so the Baader D-ERF which does not compromise the optics of your system.

An infrared reflection compensation (dielectric interference layer system with many individual layers), prevents the penetration of heat into the telescope tube. The blocking of IR (thermal radiation) holds the D-ERF filters coplanar even after prolonged observation period. Thermally induced air turbulence in the tube is prevented. Above all, the D-ERF filter protects the expensive H-alpha etalon filter against focus shift and against premature aging caused by heat stress. In addition, the centre wavelength, which otherwise with the change of temperature drifts constantly, is stabilized.

D-ERF filters are non-reflective and multilayer. They use the best possible layer system with 0.2% residual reflection to prevent reflections on the plane surfaces, that and would reduce the contrast of the solar image on the surface and the protuberances. To such a create exact plane surface and to obtain the planarity despite the applied forces through the different layers of coating, a high technical effort is necessary. From a large amount of raw glass only the best pieces that have tension-free annealed quality are chosen. If the greatest of care is not taken at every stage of production, the glass deforms with improper preparation of the coating on older evaporation systems. The final product is therefore almost useless. Baader D-ERF filters are coated on modern ion beam-supported systems in order to keep the thermal load on the glass as low as possible and still provide an extremely hard, scratch-resistant coating.

Baaders D-ERF filters are exceptional solar energy rejection filters that are made in Germany

Made from plane parallel circular disks, both surfaces are precision optically polished to 1/10 Lambda. Typically, common absorbative glass type ERF filters are only 1/4~1/5 Lambda which can have a detrimental effect on the optical quality of the system, not so the Baader D-ERF which does not compromise the optics of your system.

An infrared reflection compensation (dielectric interference layer system with many individual layers), prevents the penetration of heat into the telescope tube. The blocking of IR (thermal radiation) holds the D-ERF filters coplanar even after prolonged observation period. Thermally induced air turbulence in the tube is prevented. Above all, the D-ERF filter protects the expensive H-alpha etalon filter against focus shift and against premature aging caused by heat stress. In addition, the centre wavelength, which otherwise with the change of temperature drifts constantly, is stabilized.

D-ERF filters are non-reflective and multilayer. They use the best possible layer system with 0.2% residual reflection to prevent reflections on the plane surfaces, that and would reduce the contrast of the solar image on the surface and the protuberances. To such a create exact plane surface and to obtain the planarity despite the applied forces through the different layers of coating, a high technical effort is necessary. From a large amount of raw glass only the best pieces that have tension-free annealed quality are chosen. If the greatest of care is not taken at every stage of production, the glass deforms with improper preparation of the coating on older evaporation systems. The final product is therefore almost useless. Baader D-ERF filters are coated on modern ion beam-supported systems in order to keep the thermal load on the glass as low as possible and still provide an extremely hard, scratch-resistant coating.

We supply the D-ERF filter together with a custom housing made to fit your telescope. The housing features a three point mounting system to securely hold the cell to your telescope. This mounting is made to be an exact fit for the dew sheild of your telescope allowing the filter to be properley secured and centered.

As all filter cells are made to order there is a lead time of approx 3 weeks. Please contact us so we can discuss the exact size requirements needed to fit your telescope. The cost of this cell is based on a tube size range of 231-260mm

This is a custom made cell to take a Baader 135mm D-ERF Energy Rejection Filter. It is made to fit dew shields with a 167mm diameter. Typically this means it will fit all OTA's produced by United Optics for 125mm Optics.

By acting as both an aperture stop and ERF, the cell permits a wider range of scopes to be converted for use with rear mounted H-Alpha filters for solar observing and imaging.

When fitted the 135mm D-ERF provides an aperture of 125mm.

This ERF cell is recommended for use with the Tecnosky 125mm ED Doublet Refractor (and also the TS Optics 125mm Doublet and Altair 125 EDF). When used with this as a solar telescope the focal ratio becomes F31.2 (using a Baader TZ-4) and F33.54 (using a Quark).

This is a custom made cell to take a Baader 160mm D-ERF Energy Rejection Filter. It is made to fit dew shields with a 186mm diameter. Typically this means it will fit all OTA's produced by United Optics for 150 / 152mm Optics.

By acting as both an aperture stop and ERF, the cell permits a wider range of scopes to be converted for use with rear mounted H-Alpha filters for solar observing and imaging.

When fitted the 160mm D-ERF provides an aperture of 155mm. When fitted to the following OTA's the focal ratio will change as follows;

APM Telescopes 152mm F7.9 Doublet Apochromat. Standard focal ratio remains F7.8 (with Baader TZ-4 this is F31.6)

​Tecnosky 152mm F7.9 Triplet Apochromat. (also TS-Optics 152mm ED Triplet and 150mm Doublet, Altair Wave 152mm ED Triplet and 150mm EDF Doublet). Standard focal ratio remains F7.8 (with Baader TZ-4 this is F31.6)

APM-LZOS 152mm F7.9 Triplet Apochromat (Aluminium Tube). Standard focal ratio remains F7.8 (with Baader TZ-4 this is F31.6)

This is a custom made cell to take a Baader 135mm D-ERF Energy Rejection Filter. It is made to fit dew shields with a 186mm diameter. Typically this means it will fit all OTA's produced by United Optics for 150 / 152mm Optics.

By acting as both an aperture stop and ERF, the cell permits a wider range of scopes to be converted for use with rear mounted H-Alpha filters for solar observing and imaging.

When fitted the 135mm D-ERF provides an aperture of 125mm. When fitted to the following OTA's the focal ratio will change as follows;

Tecnosky 152mm F5.9 Achromat (also fits TS-Optics 152mm F5.9, Altair Starwave 152 and others). Focal ratio becomes F7.17 (with TZ-4 this is F28.7, with Quark F30.85)

APM Telescopes 140mm F7 Doublet Apochromat. Focal Ratio becomes F7.84 (with TZ-4 this is F31.36, with Quark F33.71)

APM Telescopes 152mm F7.9 Doublet Apochromat. Focal Ratio becomes F9.6 (with TZ-3 this is F28.82)

​Tecnosky 152mm F7.9 Triplet Apochromat. (also TS-Optics 152mm ED Triplet and 150mm Doublet, Altair Wave 152mm ED Triplet and 150mm EDF Doublet). Focal Ratio becomes F9.6 (with TZ-3 this is F28.82)

APM-LZOS 152mm F7.9 Triplet Apochromat (Aluminium Tube). Focal Ratio becomes F9.6 (with TZ-3 this is F28.82)

This is a custom made cell to take a Baader 135mm D-ERF Energy Rejection Filter. It is made to fit dew shields with a 156mm diameter. Typically this means it will fit an Astro Physics 130mm F6.3 Refractor. It may fit other OTA's sharing this dew shield size.

By acting as both an aperture stop and ERF, the cell permits a wider range of scopes to be converted for use with rear mounted H-Alpha filters for solar observing and imaging.

When fitted the 135mm D-ERF provides an aperture of 125mm.

This ERF cell is optimised for use with the Astro Physics 130mm F6.3 Starfire Refractor. When used with this as a solar telescope the focal ratio becomes F26.2 (using a Baader TZ-4) and F28.17 (using a Quark).

UV and IR Cut Filter for digital photography.

The Astronomik UV-IR Blocker lets the full range of sensitivity of the human eye (according to DIN 5031) pass, and blocks all other parts of the spectrum in the UV and IR. The Astronomik UV-IR Blocker is the ideal choice as a luminance filter for any kind of digital photography. Because of the perfect blocking of UV and IR all optical problems in these parts of the spectrum are avoided. The filter is optimized for systems with focal ratios between f/0.5 and f/50.

The typical transmission is higher than 99%.

Main Uses

The UV-IR Blocker gives you a perfect parfocal filter for the luminance channel when combined with other Astronomik filters. It is also great as a dust protection for your telescope and camera.

A UV/IR cut filter may also be used as a cost effective solar ERF (Energy Rejection Filter) for use with refractor telescopes up to 150mm. When placed before the Etalon the UV/IR cut reflects back ot of the telescope the harmful wavelengths that would otherwise damage the Etalon.