ZWO 7nm H-Alpha 36mm circular unmounted filter

The ZWO H-alpha 7nm narrowband filter is designed for astrophotography and focuses on a wavelength of 656nm. It can be used in combination with O-III and S-II filters to produce "Hubble-like" images. By selectively reducing the transmitted wavelengths, this filter eliminates the effects of public lighting and the Moon.

Its FWHM (Full Width at Half Maximum) of 7nm allows for a significant contrast gain compared to the sky background on celestial objects emitting in H-alpha. It reduces the intensity and number of bright stars in the image field and also allows for increased contrast of hydrogen nebula extensions.

The aluminum cell is manufactured by CNC machines that impose high manufacturing precision. The filter is available in 4 formats: threaded 31.7/50.8mm and 31mm/36mm circular unmounted.

Technical Characteristics

• H-alpha line transmission (656.3nm): 90%
• Bandpass: FWHM 7nm (+/-0.5)
• Infrared cutoff (700/1100nm)
• Schott glass
• Thickness of the glass: 1.85mm
• Precision optical polishing to ensure a precise wavefront at lambda/4 and parallelism <30" of arc on both surfaces
• Anti-reflection treatment

Usage

This filter is incompatible with visual observation and silver halide photography. However, it excels at enhancing the contrast of nebulae in CCD imaging, digital photography (modified camera), and webcam/video (deep sky).