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ADC v no ADC on Venus UV imaging

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About this observation
Observer
Martin Lewis
Time of observation
15/04/2020 - 18:44
Object
Venus
Observing location
St Albans
Equipment
444mm Dobsonian
ASI290MM
Baader Venus filter (type 2)
Tags

Illustration of the benefit of using an atmospheric dispersion corrector (ADC) on UV imaging of Venus. Identical processing for both. Even at 40° altitude it helps improve surface detail.

Even though the Baader Venus filter filter bandpass is only 60nm wide, the change in atmospheric refraction with wavelength is dispersion is high at these shorter wavelengths. As a result you get some vertical smearing as the atmosphere acts like a giant prism.

Note on the R image the sharp right hand side (vertical edge) but the blurred bottom edge (hztl). Also note the asymmetric horns that result too from not correcting for the dispersion.
Martin

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