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S2S, I really don't know. All I know is that my good barlows do not introduce false colour - actually they usually improve colour correction near the edge of field of widefield EPs.
I have a Televue 1.8x barlow and a Japanese 2" 2x barlow (equiv to UO 2" or Orion Deluxe 2"). They are both excellent. I also have a Meade #140 3-element apo barlow which is defective and I use it only as an extension tube with lenses removed - bad astigmatism on and off axis. And I also have a 5x powermate that is waiting for a webcam + laptop (not much use for visual but tried it with 25mm Antares plossl and it works well).
Some imagers swear by the Powermates and are getting excellent results as you can see from the Saturns and Jupiters they manage to capture. Bird uses a powermate to image planets. I reckon he would know if and why it's better than a normal barlow.
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