If you've spent any time in astrophotography communities online, you'll have come across the advice to use a "modified" camera for deep-sky imaging. The modification in question is a full spectrum conversion — the removal of the camera's internal infrared cut filter. For astrophotography, this single change makes a profound difference to what your camera can capture. Here's why. For a broader introduction to full spectrum cameras, read: What is a Full Spectrum Camera?
The Problem with Standard Cameras for Astrophotography
Every digital camera sensor is naturally sensitive to a broad range of light, including near-infrared wavelengths and, crucially for astrophotography, the deep red end of the visible spectrum. To make cameras produce images that look natural to the human eye, manufacturers place an infrared cut filter — also called a hot mirror — directly in front of the sensor. This filter blocks wavelengths above approximately 650–700nm.
For everyday photography, this is exactly what you want. But for astrophotography, it creates a serious problem.
One of the most important wavelengths in deep-sky imaging is hydrogen-alpha — a specific wavelength of red light at 656.3nm emitted by ionised hydrogen gas. Hydrogen is the most abundant element in the universe, and vast clouds of it — emission nebulae — glow with hydrogen-alpha light across the night sky. The Orion Nebula, the Rosette Nebula, the Eagle Nebula, the Lagoon Nebula — all of these iconic deep-sky objects emit strongly in hydrogen-alpha.
The problem is that the IR cut filter in a standard camera blocks a significant portion of hydrogen-alpha light. Depending on the specific camera, a standard unmodified camera may transmit only 20–25% of the hydrogen-alpha signal that reaches the lens. The rest is absorbed by the filter and never reaches the sensor. The result is that emission nebulae appear faint, washed out, and lacking in detail compared to what a modified camera can capture.
What a Full Spectrum Conversion Changes
When the IR cut filter is removed during a full spectrum conversion, the sensor is free to detect the full range of light that reaches it — including the hydrogen-alpha wavelength at 656.3nm. A full spectrum converted camera typically transmits 90% or more of the hydrogen-alpha signal, compared to 20–25% for a standard camera.
In practical terms, this means:
- Emission nebulae appear dramatically brighter and more detailed — structures that are barely visible in images from a standard camera become vivid and well-defined
- Shorter exposure times are needed to capture the same amount of nebula detail — or alternatively, much more detail can be captured in the same exposure time
- The red and pink tones of emission nebulae are rendered accurately — rather than appearing pale or washed out as they do through a standard camera's filter
- Fainter nebulae become accessible that would require impractically long exposures with a standard camera
The difference is not subtle. Side-by-side comparisons of the same nebula imaged with a standard and a full spectrum camera are striking — the full spectrum image typically shows several times more nebula detail and far richer colour.
The Hydrogen-Alpha Wavelength Explained
Hydrogen-alpha (Hα) is the name given to a specific spectral emission line produced when hydrogen atoms transition from their third to second energy level. This transition releases a photon of light at precisely 656.28nm — a deep red wavelength at the very edge of what the human eye can perceive.
In space, vast clouds of hydrogen gas are ionised by the ultraviolet radiation from nearby hot, young stars. As the ionised hydrogen recombines, it emits light at characteristic wavelengths — most prominently at hydrogen-alpha. This is why emission nebulae — regions of ionised hydrogen gas — glow red in astrophotographs. They are literally glowing with hydrogen-alpha light.
Because 656.28nm sits right at the edge of the visible spectrum and into the near-infrared, it falls precisely in the range that standard camera IR cut filters are designed to block. This is why the modification matters so much for nebula photography specifically — the most scientifically and aesthetically important wavelength for deep-sky imaging is exactly the one that standard cameras suppress.
Full Spectrum vs Dedicated Astronomy Cameras
It's worth understanding where a full spectrum converted DSLR or mirrorless camera sits in the astrophotography ecosystem. At one end of the spectrum are standard unmodified cameras — capable but limited for nebula work. At the other end are dedicated cooled astronomy cameras — highly sensitive, low-noise instruments designed specifically for deep-sky imaging, but expensive and requiring specialist software and equipment to use.
A full spectrum converted mirrorless camera sits in an excellent middle ground. It offers dramatically improved hydrogen-alpha sensitivity compared to a standard camera, while remaining familiar and intuitive to use, compatible with standard camera lenses, and capable of producing excellent results for a wide range of astrophotography subjects. For many astrophotographers — particularly those starting out or working on a budget — a full spectrum converted camera is the ideal tool.
Beyond Hydrogen-Alpha — Other Astrophotography Benefits
Hydrogen-alpha sensitivity is the primary reason astrophotographers modify their cameras, but it's not the only benefit of a full spectrum conversion for deep-sky imaging:
Improved Overall Red Sensitivity
The IR cut filter suppresses not just hydrogen-alpha but the entire red end of the spectrum. A full spectrum camera has improved sensitivity across all red wavelengths, which benefits the rendering of any red or pink nebulosity — not just pure hydrogen-alpha emission.
Other Emission Lines
While hydrogen-alpha is the most important, other emission lines also fall in the red and near-infrared range. Sulphur-II (SII) at 672nm is another important emission line used in narrowband astrophotography — the famous Hubble Palette uses SII, Hα, and OIII to create the iconic false-colour images of nebulae. A full spectrum camera has improved sensitivity to SII as well as Hα. For more on narrowband imaging, read: Light Pollution and Astrophotography — How Narrowband Filters Can Help.
Near-Infrared Deep-Sky Imaging
Some deep-sky objects emit or reflect strongly in the near-infrared. A full spectrum camera with an appropriate infrared filter can be used for near-infrared deep-sky imaging, revealing detail that is invisible in visible light — particularly in dusty regions where infrared light penetrates dust clouds more effectively than visible light.
What About Colour Balance?
A common concern about using a full spectrum camera for astrophotography is colour balance. Without the IR cut filter, the camera's colour balance is affected — images of daylight scenes have a red or magenta cast. For astrophotography, this is largely irrelevant, as colour calibration is performed in post-processing using reference stars or dedicated calibration tools. The improved hydrogen-alpha sensitivity far outweighs any colour balance considerations.
For photographers who want to use the same camera for both astrophotography and standard daytime photography, an external IR cut filter attached to the lens restores normal colour balance for daytime use.
Ready to Get Started?
Once you have your full spectrum camera, the next steps are getting your settings right and choosing the right lenses. Read our guides: The Best Settings for Astrophotography with a Full Spectrum Camera and The Best Lenses for Astrophotography with a Full Spectrum Camera.
Explore our range of full spectrum converted cameras to find the right body for your astrophotography journey.