The larger the opening of your telescope, the more sunlight and heat will enter. For H-alpha observations, that is a problem, because the narrow band filter at the back cannot handle it well. With the DayStar ERF E-325F90 for the opening, you can capture that: the filter blocks ultraviolet and infrared light and lets the red light through, where the H-alpha filter works with it.
The filter works together with an H-alpha filter at the back of the telescope, such as a DayStar Quark or a Quantum PE H-alpha filter. The ERF itself comes for the opening, on the tube or the mist cap.
Measure the outer diameter of your tube or diffuser and compare it with the specified size of the fitting. An ERF itself is not a solar filter to look at: never look at the sun without the complete filter setup. If you are unsure about the correct setup, first read the instructions. Which solar filter fits your telescope or contact us.
A measure that you can place next to it is the ERF pre-filter E-281F80.
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