Optolong H-ALPHA 6.5nm filter

The 7nm H-ALPHA filter is the most popular narrowband filter that allows a 7nm bandwidth centered on a 656nm wavelength and reduces the transmission of certain wavelengths of light, especially those produced by artificial light, including mercury vapour, both low and high pressure sodium vapor lamps and unwanted natural light caused by the emission of neutral oxygen into our atmosphere (eg Skyglow).

The H-ALPHA astrophotography filter remains the best choice for the highest contrast and for revealing fine nebula detail.

Main use and performance

Suitable for viewing low emission nebulae in H-ALPHA lines under moonlight or heavy light pollution conditions.

Narrowband imaging can be obtained by combining the filters of the SHO set (H-ALPHA, OIII, SII), in lunar and light pollution conditions, in this way the equipment does not remain stationary for weeks .

The H-ALPHA filter is the first filter that is usually added to the LRGB KIT by most astrophotographers, in this way they mix the black and white image with the RGB data to obtain and improve the structural details while maintaining a natural look of the image. .

The H-ALPHA filter does not eliminate the effects of light pollution and does not increase the brightness of the photographed object, but rather increases the contrast between the nebula and the night sky, which facilitates image processing .

This H-ALPHA 7nm narrow band filter is designed for use in filter wheels, in filter holder drawers or directly on the camera (not valid for those not mounted in the cell)
Technical characteristics

Technical data

•     Schott substrate material
•     Thickness 2.0mm (1.25"/2"/36mm)
•     Thickness 1.0 mm (Clip series)
•     Surface quality: 60/40 (refer to MIL-O-13830)
•     Fine optical polishing to ensure accurate 1/4 wavefront and <30 seconds parallelism on both surfaces
•     80% transmittance to the h-alpha line Infrared wavelength of 656 nm, cut-off 700 to 1100 nm
•     0.1% transmittance of out-of-band artificial light pollution, especially large emission lines (i.e. Na 589 nm, Hg 435 nm and 578 nm). A transmission of 0.1% is equivalent to OD3 (optical density), and a high optical density value indicates very low transmission and a low optical density indicates high transmission.