Stopping down the aperture can be a useful strategy to reduce the worst effects of CA on very bright objects as you have found using the central hole. The worst of the CA is generated in the outer sections of the lens, particularly from a diameter of 120mm outwards. When you have your scope, experiment with different size aperture masks made out of cardboard with say, 100, 110 and 120 mm diameters to see which gives you the best balance between CA and the lower light and resolution that results from the smaller aperture. The simple central hole in your lens cap is likely to make Moon and planetary views too dim if you want to reduce the CA.
You might find that an aperture stop of around 120mm is only needed for the Moon and the very bright Jupiter around opposition. All the rest you enjoy the full 150mm aperture.
Quote:
Originally Posted by jimmyh1555
Another thing about the CA problem is so simple. The lens cap comes with another capped hole in the middle. The instructions said to see a bright star, just put the cap on and use the small hole to cut down the aperture. I tried it on Sirius and hey presto, no C.A.!!!
So out goes the Newt, and in comes the 150mm XLT! PS, I only want this one for visual - I have got the 100mm Esprit for AP 
My XLT 120 I shall use for Mr Moonie! |