ZWO 7nm NARROWBAND FILTER SET
ZWO
ZWO 7nm NARROWBAND FILTER SET - 1.25" is backordered and will ship as soon as it is back in stock.
ZWO 7nm narrowband filters enhance the contrast of emission and planetary nebulae. These peculiar nebulae emit light only in specific wavelengths (H𝛼; OIII; SII) and the narrowband filters have the property to reject all light outside these bands.
The passing band or "window" of these filters is 7nm wide. Considering that the visible light spectrum is between 380nm and 740nm, a 7nm filter would block 98% of the unwanted light. As a result, the signal to noise ratio between the light of the nebulae (signal) and the noise (moonlight, light pollution, airglow) is highly increased.
Nebulae have a strong emission on the band of the ionized hydrogen (H𝛼), doubly ionized oxygen (O III) and the ionized sulfur (S II). Having 3 wavelengths in 3 different areas of the visible spectrum, it is possible to recreate a false colour image of a nebula.
These filters cut off infrared and ultraviolet light so the IR-UV cut filter is not necessary.
The O III filter can also be used for visual observations as the human eye is sensitive at this wavelength.
Specifications
| Passing band |
7 ± 0.5nm (FWHM) |
|
Glass thickness |
2.0 ± 0.03 mm |
|
Optical flatness |
1/4 λ (wavefront) |
|
H𝛼 transmission |
About 90% at 656 nm |
|
O III transmission |
About 90% at 500 nm |
|
S II transmission |
About 90% at 672 nm |
|
Transmission off-band |
<0.1% OD3 (Optical Density) |
