Ever since I’ve started astrophotography, I’ve been wanting to photograph nebulas. Probably the most well known nebula is the Eagle Nebula, beautifully represented in the iconic ‘Pillars of Creation’ taken by the Hubble Telescope in 1995.
Naturally, the pillars don’t have that green background and the pillars aren’t that rust-brown colour. This is a specially colour palette, called the Hubble Palette; it is a way of representing different elements that are found in the nebula. Hydrogen-Alpha is represented as green, Oxygen-III is blue, and sulphur-II is red. There are other palettes in the Astrophotography-world that put the elements with either red, green or blue channels, but the Hubble Palette is the most common.
Right, a bit of a science lesson!
These emission nebulas are the birthing place of new hot stars, that release insane amounts of UV energy. This energy ionises the elements in the dust clouds, especially Hydrogen atoms that are prevalent throughout the universe.
I’m going to take you back to your high school physics classes, and go through the Rutherford-Bohr model element energy states.
When stable, a hydrogen nuclei, with its single electron, orbit normally in the first energy state. However when the atom is ironised, the energy levels received allow the electron to jump energy states upto a higher level. When the electron drops back down to the original energy state, the process emits a photon of light. This photon has a specific wavelength that corresponds to the amount of energy difference between the higher state and the stable state. When the electron jumps down from the second to the first energy state, the wavelength of light released is 656.3nm and is firmly in the red part of the spectrum. That’s just a quick overview!
The elements that are associated with emission nebulas are:
- Hydrogen Alpha – Second State to First State – 656.3nm
- Hydrogen Beta – Third State to First State – 486nm
- Oxygen-III – 496nm and 501nm
- Sulphur-II – 672nm
The standard internal infrared cut-off filter is below the frequencies of Hydrogen Alpha and S-II, and therefore is completely invisible to my standard DSLR.
However, the infrared/UV filter can be removed, allowing the full spectrum of light to be photographed. The only problem is now the camera cannot be used for normal daylight photography, so I have been holding off from getting my camera modified.
While searching on the internet one evening, I managed to find an already-modified Canon 600D, along with an Astronomik CLS-CCD (City Light Pollution) filter, for an irresistible price on Facebook Marketplace. I just couldn’t refuse it! The CCD version of the Astronomik filter includes a UV and IR blocking filter, but still allows the Hydrogen and Sulphur. It is best to remove these frequencies, as it can cause star bloating when used with a refractor telescope, as the lenses cannot focus these wavelengths at the same focal point as the visible light.
This model is identical to my unmodified DLSR, so all my accessories will fit this new camera; including the T-Ring and intervalometer.
As can be seen in the images below, this has got the naked-sensor modification. This means that it’s got no glass in front of the sensor, which invertedly removes the ability to use autofocus on camera lenses. But for astrophotography, this function is redundant anyways. The Astronomik CLS CCD filter functions as the UV/IR block glass which will be permanently kept in to protect the sensor.
I can’t wait to test this camera out! So I’m sorry for everyone who is wishing for clear skies! You can blame me!
Till next time though, clear skies!