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Airylab 235mm D-ERF Filter including Custom Cell

Airylab 235mm D-ERF Filter including Custom Cell

Not in stock

Price includes VAT, plus delivery

The Airylab 235mm DERF is a specialised energy rejection filter for large aperture solar telescopes. The filter is a dielectric type similar to the Baader DERF. It's performance is tested at L/8 PTV with 90%+ transmission at the H-Alpha wavelength.

A filter of this size is ideally suited for use with a 9.25" SCT. The special design of the mounting cell only sacrifices 2mm of the maximum diameter of the filter. Alternatively it is also suitable for use with the Tecnosky 234mm Achromat.

For use with either system a telecentric is required. For the Celestron Edge SCT we recommend the Airylab 2.7x which is specially designed for the Edge series of telescopes. This can be modified to provide a 3.5x multiplier with an additional module. For a standard 'C' range SCT then the Baader TZ-3 Telecentric is recommended. For use with the Tecnosky, the Baader TZ-4 is the correct choice.

The Airylab 235mm Energy Rejection Filter is supplied with Spectrophotometer Report to confirm its quality. The price includes a custom made cell to house the ERF. Cells for a 9.25" SCT are usually available from stock. Cells to fit other telescopes can be made to order.


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 3-4 weeks. Please contact us so we can discuss the exact size requirements needed to fit your telescope.

Browse these categories as well: Safety / ERF Filters, Safety Filters