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I think Colin means achro refractors, not ED ones.
Ben , if you have only used an ED 80, any CA you've come across will have been minimal. The 150 f/8 achro has severe CA, [ as Colin said, the f/5 is even worse]. It can be reduced by using various filters, but at a cost of
lost light grasp, and, depending upon the type of filter, a colour cast.
You can reduce the CA significantly by using a barlow, but you end up with
a 2400mm f/16 scope, very very slow for imaging, and a very large image scale, requiring very accurate tracking. Even without a barlow the field of view would be about half that of your ED80, so your image would be about twice the size, and would still need better tracking than your ED80 requires.
raymo
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