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Old 27-04-2018, 09:28 AM
Wavytone
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Wavytone is offline
 
Join Date: Jul 2008
Location: Killara, Sydney
Posts: 4,147
It’s typical artefact from a fast achromatic refractor - lateral chromatic aberration seen when the subject has a sharp edge with extreme contrast (ie white vs full shadow) and is somewhat off axis. If you moved the scope to put the image on the other side of the eyepiece you’d see the shadows tinged with blue.

Try looking at stars at the same power and see what happens.

Achromatic refractors really should be f/15 - like Unitron used to do - to achieve excellent correction; the modern trend of making them around f/8 or even f/5 is a stupid compromise as opticalybsome false colour is inevitable. The downside of course is the size of the OTA and mount required.

Ways to eliminate false colour:

1. In a budget achromatic refractor, use a filter so you’re observing in 1 colour, this will also significantly improve the sharpness of the moon, visually.

2. Use an apochromatic refractor. Costs $$$ but the colour correction is vastly better.

3. Use a reflecting telescope - i see you have a lightbridge ...
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