ZWO SII 7nm 2" Filter - SII7nmD2
Narrowband filters are great for astroimagers looking to increase the contrast between the celestial object and the night sky. While these types of filters do not eliminate the effect of light pollution, they do boost the contrast between an object like a nebula and the sky around it. The ZWO 2" narrowband filters work by reducing the transmission of certain wavelengths of light that come from skyglow and artificial lighting. These are called mercury vapor, both high and low pressure sodium vapor lights, and neutral oxygen emission in our atmosphere.
ZWO's SII 7nm filters passes light at a 672nm wavelength and is fine-optically polished to ensure accurate 1/4 wavelength. With this wavelength transmission, the SII filter is most suitable for nebula observation and imaging. When it comes to visual observation, it works best with most emission nebulae, planetary nebulae, and supernova remnants. If it is used with the H-alpha and OIII filters, it is perfect for tricolor CCD astrophotography!
SII Filter Specifications
- Filter Size: 2"
- Mechanical Thickness: 7.5mm (5mm + 2.5mm thread
- Thread: M48.5x0.75 male
- FWHM: 7±0.5nm
- Transmission: About 90%
- Infrared wavelength cut-off: 700-1100nm
- Transmission of off-band: <0.1%, OD3 (Optical Density)