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Hα Filters

Baader Filter
Holder Adapter

IDAS - Hydrogen-Alpha Filter Family

The IDAS Hydrogen-Alpha family of filters allows astrophotographers to select an Hα filter optimally tailored to their equipment.

Features include:

  • 6.8 nm bandpass (measured value 6.5 +/- 0.1 nm)
  • 98% transmission (measured value)
  • IR blocking out to 1200 nm
  • 2.5mm and 3.0mm filter thickness options
  • Configurations:
    • 50.8mm for filter wheels (QHY/ZWO/Atik)
    • 48mm and 52mm mounted
    • Camera body drop-in (DI)
  • Each filter is individually measured and inspected for quality
  • 3 classes* available: STD, HS, UHS
  • Made in Japan

* The IDAS Ha-6.8 family includes 3 options - STD (Standard), HS (High Speed) and UHS (Ultra High Speed) with bandpasses adjusted to accommodate the f-ratio of different speed astrographs. In addition each class comes in two different glass thicknesses - 2.5 mm & 3.0 mm.

  • STD - recommended for most regular scopes
  • HS - ideal for the optics between F2.0 and F3.5 such as Takahashi Epsilon Series, RASA11, and standard camera lenses
  • UHS - highly optimized for the optics for F2.2 or faster such as RASA8 and HyperStar Series
Prices are the same across the filter family regardless of the option selected. Filters are designed to fit in 50.8mm QHY, ZWO and ATIK filter carousels.


Detailed Filter Plots:

The plots below show the different filter performance with various astrograph designs - refractors vs. telescopes with central obstructions.

STD- refractor STD- telescope with central obstruction (CO) HS- refractor HS- telescope with central obstruction (CO) UHS- refractor UHS- telescope with central obstruction (CO)

Each filter is uniquely identified and shipped with the plotted test results for the individual filter.



Reflection Test Sample:

This test (200 second exposure) shows clean images of bright stars in the field, indicating good anti-reflection (AR) design.



Another set of photos from the Orion belt region demonstrates the lack of reflection artifacts around bright stars.

Sigma 105mm@F2 + IDAS Ha 6.5nm HS 52mm + ASI 2600MM, 30 x 5 minutes (gain 0), Bortle 8 sky

Closeup shot including bright belt stars Alnitak and Alnilam.


Examples from Bortle 8 skies (5-minute exposures):

Cygnus wide-field.


Also from Bortle 8 skies - Simeis 147

Sigma 105mm Art @F2 + IDAS Ha6.5 HS 52mm + ASI2600MM (gain 0), 22 x 7 minutes