The Sun in Hydrogen-alpha. Close up to show detail of filament and a plage area.

A Barlow lens was used to double the magnification of the telescope. An unwanted result of this is the ripple pattern in the lower central part of the image. The Barlow lens introduces additional glass surfaces which can result in a double reflection and an extra path to the image. How the reflected and direct images combine depends on the different path lengths measured in wavelengths. If the two glass surfaces are not exactly parallel an interference pattern can result. This will only happen with light of a single wavelength as in this case of a hydrogen alpha filter being used.

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