For optimum adjustment of a telescope aperture when observing with an H-alpha filter of Solar Spectrum (also suitable for other brands). The diaphragm has four telescope-sided M3-threads on a pitch circle radius of 60 mm to fasten on a DIY-holder.
Please note: in addition to the price of the diaphragm there might be additional modification costs of EUR 50.- if we adapt the diaphragm to a self-manufactured D-ERF-filter holder (Our filter holders are available ONLY IN ADDITION to a Solar Spectrum H-alpha filter).
Other applications: The iris may of course be used to selectively dimming of a refractor objective, eg to hide the edge residual error of inexpensive lenses.
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