Artesky ERF 80 mm Filter, Glass only, Thickness 12 mm

Artesky ERF 80 mm Filter, Glass only, Thickness 12 mm

The purpose of using an Energy Rejection Filter (ERF) is to prevent as much solar energy as possible from entering the telescope, thus preventing excessive heating of the H-alpha filter etalon.

This effect can be effectively achieved by adding an ERF filter to the front of the telescope.

At the same time, it prevents the air inside the tube from heating up - the telescope remains close to room temperature and there is no air turbulence inside the tube due to the temperature difference. If we look at the solar spectrum, we see that this filter mainly blocks visible light. Ideally, it reflects solar energy rather than absorbing it, and it does not heat up in the process - that is why these filters are called Energy Rejection Filters (ERF).

Artesky ERF filters are unique in the world - their dielectric coating provides a beam of pure light, with an FWHM of 60 nm!

The glass substrate in this case is not of any soft, colored absorbent type with streaks, but transparent of the highest homogeneity, finely polished to the quality grade of objective lens surfaces and with all performance reflective coatings on one side.

This reflects the entire desired spectrum from 300 nm up to 1100 nm, leaving open only that 60 nm wide spectral window around H-alpha (656.28 nm).

If these coating systems on both sides of the plate are not properly executed, to cancel the stresses induced by the coating layers, the surfaces parallel to the plane can be easily distorted, which means that the flat 1/10-wave plate is distorted into an irregular substrate curve that will act like a bad objective.

The filter layers of the Artesky ERF are designed with the utmost care, applied with the world´s most advanced optical coating machines.

This level of attention preserves the resolving power of the entire telescope objective aperture, dramatically reducing the thermal energy that passes through the telescope and reaches the solar spectrum filter.

Not only is this the main reason for the significant reduction in thermal stress inside the telescope, but it also greatly decreases heat-induced visual effects.

Important Note:

Artesky ERF Energy Rejection filters are intended for use only as a prefilter for solar spectrum H-Alpha filters.

The ERF filter must always be present and mounted in front of the telescope objective.

The filter should be oriented with the main coating surface facing the sun (an arrow on the edge of the filter points to this side).

The ERF should be used in conjunction with Daystar H-Alpha filters or similar.

If the ERF is used alone for visual observation, irreparable eye damage will occur.

Practical Note: This filter is sold without a cell, if you need the version with the cell already included look for it in the "Solarfilter for H-Alpha and Calciuim" section or contact us.

Safety informations: PDF Download