Astro Conversion Types Guide

Posted by Daniel Amado on

MODIFICATIONS TYPES EXPLAINED

 

DSLR Modification for astrophotography

 

A DSLR or Mirrorless Camera modification for Astrophotography consist of the Hydrogen Alpha wavelength bandpass transmission increase at 656nm emission line and the Sulfur II wavelenght transmission increase at both 671.7nm and 673nm emission lines. The original UV/IR Blocking filter present on stock DSLR or Mirrorless Cameras only allows over 25% transmission of H-alpha emission line and over 15% of Sulfur II emission lines. An Astro-Converted DSLR or Mirrorless Camera is about 4 and 6 times (H-alpha and Sulfur II respectively) more sensitive to the deep reddish nebulae structure tones. H-alpha objects/sections are also present in all the other galaxies besides the Milky Way. The hydrogen element is present in the entire universe, and many emission nebulae visible on the night sky emanate hydrogen alpha emissions.

 

 

SENSOR FILTERS ASSEMBLY DIAGRAM

 

 

The internal sensor filter assembly is comprised by the following elements:

  • Retaining clip plate (support material)
  • Low pass filter (also known as LPF1, Anti-Aliasing or dust removal filter)
  • UV/IR Blocking filter* (LPF2, Hot UV/IR, Color limiting filter, Bluish filter)
  • Filter gasket seal
  • Sensor filter frame housing
  • CMOS Sensor

 

STOCK UV/IR BLOCKING SENSOR FILTER

 

 

Among all the sensor assembly elements listed above, for a substancial increase of Hydrogen Alpha and Sulfur II emissions, *the UV/IR blocking bluish sensor filter has to be removed. This is what the Astro-Conversion is all about. As can be seen in the graph below, light transmission on the red wavelegth spectrum is greatly reduced after 500nm towards the infrared spectrum. This is why the original UV/IR blocking sensor filter is also called color limiting filter, it is the culprit for suppressing most of the H-alpha and Sulfur II emissions. The purpose of this filter is redering a natural color balance on the camera images output imitating the colors' appearence to what the human eyes see.

 

  

 

 

LOW PASS FILTER

 

 

Also known as LPF1, Anti-Aliasing filter or Dust removal filter, it also blocks Ultraviolet and Infrared light and has the piezoelectric device that triggers vibrations to shake off dust particles. The main purpose of the Low Pass Filter is eliminate moire effect but at the cost of sacrificing sharpness slightly introducing a little blur effect and it also reduces color noise. Digital cameras without low pass filter have the piezoelectric sef-cleaning device attached directly to the UV/IR blocking filter. 

 

 

 

1A. UV/IR blocking bluish filter removal with LPF

(Enhanced Spectrum: Visible + H-Alpha + Sulfur II)

 

 This conversion preserves the Low Pass Anti-Aliasing filter with self-cleaning function on cameras with Low Pass Filter. The spectral sensitivity of the camera sensor will be Enhanced Spectrum (For a complete description of a ES conversion please read options 2A or 2B), allowing Hydrogen Alpha and Sulfur II wavelength emissions pass but still blocking UV/IR light. With the Low Pass Filter only preserved, in most cases the sensor distance to the lens bayonet can be adjusted accordinly to match the diffraction index differential to reach perfect focus to infinity with lenses. The sensor repositioning distance range can be confirmed once the camera is disassembled. Perfect focus of subjects closer than infinity will always be achieved in Live View Mode, but for focus to infinity with lenses capability including autofocus with Pentaprism/Pentamirror mode using DSLR cameras, option 2A is guaranteed for all models and options 2B and 3 are guaranteed for most models with very few exceptions (Like Full Frame Mirrorless Canon EOS R Series). Telescopes will always reach focus to infinity without any problem. 

 

1B. UV/IR blocking bluish filter removal without LPF

(Full Spectrum: Ultraviolet + Visible + H-Alpha + Sulfur II + Infrared)

 

This is the most unexpensive conversion, most recommended to save money. Cameras without the LPF or when it is removed having the sensor bare or "naked" will become Full Spectrum (For a complete description of a FS conversion please read option 3).

Without any glass above the sensor there are no internal reflections coming from a replacement filter. When the stock UV/IR blocking filter is removed, the surface of the sensor is not really naked. There is a layer of glass protecting the micro-lenses and bayer filters on top of the pixels. 

 

The "Clip-in Mod" explained 

With the bare sensor modification, the sensor distance to the lens bayonet will be adjusted to reach focus to infinity and autofocus calibration in Pentaprism/Pentamirror mode with DSLR cameras when a Clip-in body filter like the Astronomik L-2 UV/IR blocking is attached to the camera body (Subject to lens and camera model compatibility, all telescopes are compatible). Internal UV/IR blocking luminance filter and internal clear glass modifications (Options 2A,2B and 3) are compatible with all lenses, cameras and telescopes. When combined with a Clip-in filter like the Astronomik L-2 UV/IR blocking or the Clip-in MC Clear glass, the total price of this conversion is less than the internal filters modifications.

 

 

 2A. Enhanced Spectrum conversion with Baader or AstroGear Luminance Filter and LPF 

(Visible + H-Alpha + Sulfur II)

 

For this conversion, the non-detachable Baader or AstroGear UV/IR Cut Anti-Reflective filter (Depending on filter availability) with enhanced H-alpha and Sulfur II sensitivity is permanently installed preserving the Low Pass Anti-Aliasing Filter with self-cleaning function. This is the most convenient modification for wide field astrophotography with lenses because autofocus and focus to infinity with lenses is guaranteed in all Canon models. The sensor filters configuration of this modification is the same of the Canon EOS 60Da and Canon EOS Ra. This conversion does not require an additional or external UV/IR Cut filter. The camera can be used for daylight photography setting the custom white balance with a gray card shot under the specific light source for "In-Camera" white balance correction or with Adobe Camera Raw white balance presets without the need of additional original white balance filters.

Out of focus NIR: With the Enhanced Spectrum modification, depending on the lens, telescope or optical corrector used, some imagers might experience a little bit bloated stars due to the near infrared light slightly out of focus when a refractive optical system does not have at least one ED (Extra-Low Dispersion glass) element. This chromatic aberration could be mitigated with post processing correction using computer software.

 

 

 

2B. Enhanced Spectrum Conversion with Baader or AstroGear Luminance Filter only

(Visible + H-Alpha + Sulfur II)

 

On this conversion both Low Pass Anti-Aliasing filter with self-cleaning function and the UV/IR blocking bluish filter are removed and replaced by the non-detachable Baader or AstroGear UV/IR Cut Anti-Reflective filter (depending on filter availability or camera model) with enhanced H-alpha and Sulfur II sensitivity. With the permanent installation of this filter, this conversion does not require an additional or external UV/IR Cut filter. Perfect focus to infinity with lenses capability including autofocus with Pentaprism/Pentamirror mode is guaranteed for most cameras models with very few exceptions (Like Full Frame Mirrorless Canon EOS R Series). Telescopes will always reach focus to infinity without any problem. The camera can be used for daylight photography setting the custom white balance with a gray card shot under the specific light source for "In-Camera" white balance correction or with Adobe Camera Raw white balance presets without the need of additional original white balance filters.  With the Low Pass Anti-Aliasing Filter removed, the Camera Sensor performs at native maximum sharpness, which is also great for solar and planetary astrophotography. Astrophotography dedicated cooled cameras have the same sensor filter configuration of this conversion having an UV/IR blocking filter with the same transmission range without any low pass filter. 

Out of focus NIR: With the Enhanced Spectrum modification, depending on the lens, telescope or optical corrector used, some imagers might experience a little bit bloated stars due to the near infrared light slightly out of focus when a refractive optical system does not have at least one ED (Extra-Low Dispersion glass) element. This chromatic aberration could be mitigated with post processing correction using computer software.

 

3. Full Spectrum conversion with Astronomik Anti-Reflective Clear Glass only

(Ultraviolet + Visible + H-Alpha + Sulfur II + Infrared)

 

 

 

The Full Spectrum modification is the best conversion for planetary astrophotography because the possibility of using infrared isolating filters like the Astronomik ProPlanet 742 IR-pass and 807 IR-pass . The infrared wavelength is significantly less susceptible to poor seeing (atmospheric turbulences) and consequently the resulting images are considerably sharper. Expert planetary imagers process planets photos with single line infrared filters as a luminance channel. 

 

 

 

 

This is the most versatile conversion, is suitable for UV/IR Photography, Regular Photography and Astrophotography. The camera will capture the entire visible spectrum including Hydrogen Alpha and Sulfur II emissions plus ultraviolet and infrared light. Perfect focus to infinity with lenses capability including autofocus with Pentaprism/Pentamirror mode is guaranteed for most cameras models with very few exceptions (Like Full Frame Mirrorless Canon EOS R Series). Telescopes will always reach focus to infinity without any problem. Both Low Pass Filter with self-cleaning feature and the original UV/IR blocking bluish filter are replaced by the non-detachable Astronomik Multicoated Anti-reflective Clear filter which is permanently installed. With the Low Pass Anti-Aliasing Filter removed, the Camera Sensor performs at native maximum sharpness.

 

 

Out of focus Infrared: An additional UV/IR cut filter is required to capture the pictures in visible light. This filter is a must when imaging with telescopes using refractive elements (refractors, catadioptrics, reducers/flatteners, coma correctors, etc.) If light frames are captured without an UV/IR blocking filter you will get bloated stars, because UV and IR light rays focus at different distance from the visible light focal plane.

A luminance filter, or any narrowband filter will cut off Ultraviolet and Infrared Wavelengths. With a Ritchey-Chretien Telescope and no flattener/reducer there is no need of an additional UV/IR Blocking filter.

For daylight or regular photography an additional Original White Balance filter is required. The Astronomik OWB Clip filter can be used to correct White Balance (Subject to lens and camera model compatibility).

 

To browse our Astro Conversions options click here


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