Sensor Infrared Cut Filter (IR-Cut) Physical Light Transmission and Astronomy Deep-Sky Modification (Ha 656nm / Dual Narrowband Filter) Principle

1. The most magnificent color in the universe: Why is your camera "blind" to the red nebula?

An ordinary camera exposes the Orion Nebula and the Horsehead Nebula for 10 minutes, and the nebulae captured are dim and gray:

1. The spectral miracle of ionized hydrogen alpha line (H-Alpha 656.3nm):

• More than 90% of the magnificent deep space emission nebulae in the universe have excited ionized hydrogen atoms at their core;
• During the electronic transition of hydrogen atoms, deep red visible light with a wavelength of exactly 656.28 nanometers (nm) is released;

2. Original camera’s “IR-Cut Filter”:

• The silicon sensor itself can sense infrared light up to 1100nm;
• If not blocked, wearing chemical fiber clothes for daily shooting will cause the light to change color and the plants to turn white;
• Therefore, camera manufacturers install an extremely thick infrared cut filter (Hot Mirror) on the CMOS surface;
• This filter starts cutting off a cliff from 600nm, and when it reaches 656.3nm, the light transmittance has been brutally reduced to less than 20%~25%**!
• Three-quarters of the most precious and bright nebula photons in the deep space of the universe are directly intercepted and rebounded by the original glass!

2. Three major hardware modification schools for Tianwen modified machines

Deep space photographers must disassemble the main board of the fuselage and perform "minimally invasive surgery" on the glass on the sensor surface:

1. BCF/Baader Astronomy Modification (the most recommended solution for daily use):

• Remove the original factory's over-cut first-layer low-pass filter and replace it with a piece of precision-customized German Baader optical glass;
• This piece of glass perfectly transmits all visible light between 400nm and 680nm, causing the transmittance of the 656.3nm Ha line to instantly increase from 25% to more than 98%! **
• At the same time, it still cuts off useless thermal infrared above 700nm; for daily photography, you only need to customize the white balance to restore normal skin color.

2. Full Spectrum Modification:

• Remove all filters in front of the sensor and replace with a piece of pure quartz high-transmission white glass;
• Allows barrier-free passage of all wavelengths from 350nm ultraviolet to 1100nm infrared;
• There are many ways to play, but for daily photography, you must re-screw the UV/IR Cut filter in front of the lens.

3. Actual combat of fine-tuning the flange distance and dual-narrowband filter (Dual-Narrowband) after modification

1. Glass thickness optical compensation and infinity focusing:

• When the original piece is removed, a new piece of glass with exactly the same optical refractive thickness must be replaced. Otherwise, the refraction displacement of the optical path will change, and the ordinary lens will completely lose its ability to focus at infinity!

2. With dual narrowband light pollution filters (such as L-eNhance / L-eXtreme):

• On urban balconies with serious light pollution, the dual narrow-band filters only let in 656nm (Ha) and 500nm (OIII oxygen three), forcibly filtering out all urban sodium lamp LED stray light. You can also take stunning deep-sky Rosette Nebula from your own balcony!

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