There are several types of OSC deepsky filters in the Altair range, but there is no perfect filter for any conditions. This guide helps you choose the correct filter for your sky conditions:
- Dual-Band – the allowing only the thinnest peaks of Ha 656.3nm and 500.7nm Oiii light from emission nebulae through with the highest OD blocking of unwanted visual and UV/IR wavelengths. Dual-Band is recommended for extreme light pollution in the worst possible conditions such as a city centre with severe LED light pollution, but also can be used under any skies for maximum contrast.
- Tri-Band – combines Ha into a “red zone”, and H-beta + Oiii into a “green/blue zone”. Combats urban and suburban light pollution at a reasonable price.
- Quad Band – combines Sii AND Ha into a red zone, and H-beta + Oiii into a green/blue zone. For suburban / moderate light pollution.
- LPROMAX – allows all nebulae emission bands through, but suppresses the worst light pollution emission lines such as mercury and sodium vapour streetlights. Also supresses airglows and generally improves contrast, whilst still allowing some natural star colours, although as usual, colour balance adjustments are required to bring them out.
- TRI-RGB – allows all nebulae emission bands through, and increases general deepsky contrast, but importantly allows accurate star colours for maximum aesthetic effect on broadband targets such as galaxies, reflection nebulae and star clusters. Reduces light pollution and moonglow to some extent and improves signal to noise ratios in any conditions.
| Filter type: | Dual Band Ha Oii | Dual Band Sii Oii | TriBand V2 | QuadBand V2 | LPROMAX | Tri-RGB |
| Fastest Focal Ratio compatibility*:
*Under constant review. Read further article here: The effects of telescope focal ratio on light pollution filter performance. |
4nm F4.0+
6nm F3.5+ |
4nm F4.0+
6nm F3.5+ |
F1.8 (slower is better) | F1.8 (slower is better) | F1.8 (slower is better) | F1.8 (slower is better) |
| H-alpha 656.3nm : | Y | Y | Y | Y | Y | |
| Oiii 500.7nm : | Y | Y | Y | Y | Y | Y |
| Oiii 495.9nm : | Y | Y | Y | Y | ||
| Sii 672nm : | Y | Y | Y | Y | ||
| Star colours: | N/A | N/A | N/A | N/A | Yes | Strong |
| Max Bortle rating (subjective estimate!): | 9-0 | 9-0 | 7-0 | 5-0 | 7-0 | 6-0 |
