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How Does the Pierro Astro ADC Work?

When light from the planets or stars passes through the Earth's atmosphere (fig 1), it is "refracted," (deflected at an angle which is dependent on its wavelength). This effect, similar to a prism, causes a significant colour shift  known as Chromatic Aberration. This is very detrimental to both viewing and imaging these objects.


The ADC, or atmospheric dispersion corrector (fig 2), is an opto-mechanical accessory which corrects this by using the chromatic superposition of two counter rotating prisms. It’s simplified operation is described by the small diagram below .

The levers on the ADC move the counter rotating prisms and adjust the compensation from nothing to a maximum effect when the levers are 180 degrees apart.


Different wavelengths are affected more by the dispersion effect than others.  Our ADC makes it easy to compensate for the effect simply by adjusting the levers.

When colour imaging a planet without an ADC, you will end up with colour fringing and distortion. Even if the appearance of this fringing and distortion is removed in processing, it has led  to a loss of resolution  in the image which cannot be recovered. When Mono imaging the taking of individual Red, Green and Blue Images and overlaying them helps to compensate somewhat for the  image shift. However to maximise resolution of the image a Luminance image should be taken. This will suffer from the same issues as a normal full colour image. The improvement to this can be seen in (fig 4).


By using an ADC, the distortions and image shift problems are eliminated resulting in a massively more detailed image. When processed further, this results in a final image which is dramatically improved.


In (fig 3) below, you can see how the use of an ADC affects even the individual colours because the light path is dispersed by the atmosphere.

Imaging

Fig 1 - Chromatic Aberration caused by atmosphere

Fig 2 - ADC  works in the opposite way

Camera

Sensor

Fig 3 - ADC  benefits even individual colours

Fig 4 - ADC  makes a large improvement to the Luminance channel

Images for fig 1, fig 3, fig 4 and Fig 5 are reproduced with the permission of Martin Lewis. More information about  his experiences of using an ADC can be found on his website http://www.skyinspector.co.uk/index.htm

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Fig 5 - ADC  improves one shot colour imaging