Optolong Filters L2 Dual-Combo Set 2" (87712)

Optolong Filters L2 Dual-Combo Set 2" (87712)

The L2 Dual-Combo Set includes two 7 nm narrowband filters designed for astrophotography. These filters are suitable for use with one-shot color cameras such as DSLRs, as well as monochrome CCD and color CMOS cameras. They are particularly well suited for fast optical systems and also support telescope systems with an f-ratio of f/3.3 or slower.

One of the filters in this set isolates the H-alpha and Oxygen III emission lines, maximizing contrast and improving the signal-to-noise ratio when imaging nebulae. By allowing only these key wavelengths to pass, it significantly enhances nebular detail while darkening the sky background. This makes it an excellent choice for astrophotographers working in heavily light-polluted areas or during bright moon phases.

A major advantage of this dual-band design is that there is no transmission between the H-beta and OIII lines, since no important nebular emissions occur in that range. As a result, unwanted light pollution is effectively blocked, allowing nebular signals to stand out more clearly. Unlike tri-band filters that transmit H-beta, H-alpha, and OIII simultaneously, this dual-band filter focuses specifically on H-alpha and OIII for improved isolation and contrast.

The second filter in the set is also a dual 7 nm narrowband design, optimized to reduce bright star halos while maintaining high transmission efficiency. After extensive technical refinement, it delivers strong performance in isolating key emission lines while suppressing unwanted wavelengths, ensuring detailed imaging of emission nebulae even under challenging sky conditions.

Key Specifications

• Number of filters: 2

• Central wavelengths: 500.7 nm, 656.3 nm, and 672.4 nm

• Bandwidth (half-value width): 7 nm

• Transmission: Greater than 85%

• Filter thickness: 1.85 mm

• Surface accuracy: 1/4 wavelength

• Frame size: 2 inch

• Mount material: Aluminium

• Optical coating: Multiple layers

• Filter type: Line filter

Application and Usage

• Suitable for astrophotography: Yes

• Suitable for visual observation: Yes

• Recommended for nebulae and galaxies: Yes

• Suitable for twin stars: No

• Suitable for Moon and planets: No