ERF pre-filter E-140N100 for H-alpha solar monitoring | DayStar

An H-alpha filter at the back of your telescope can be vulnerable to the heat of a full beam of sunlight. Therefore, an H-alpha setup starts at a larger aperture with an energy rejection filter such as the DayStar ERF E-140N100. It blocks ultraviolet and infrared light and a large portion of visible light, allowing the red light around the H-alpha wavelength to pass through.

You place the filter in front of the opening, on the tube or on a dew cap from your telescope. In the rear it works together with an H-alpha filter, such as a DayStar Quark or a H-alpha filter from the Quantum series.

First check the outer diameter of your tube or dew cap, as the fitting should fit snugly and securely, with no gaps where unfiltered sunlight can pass through. A common mistake is to think that an ERF is itself a solar filter. That is not so: use it exclusively in conjunction with a suitable H-alpha filter. You can read more about the different types in our explanation about sunscreens.