Thread: Barlows
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Old 21-05-2017, 08:02 AM
Tropo-Bob (Bob)
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Join Date: Sep 2013
Location: Cairns
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I tried a combination of eyepieces with a barlow with fast refractors that have loads of CA to answer some of my own questions .

I could see no less CA or improvement in the off-axis view I compared EPs 18mm ortho, 20mm plossl and a 12mm radian with a
2x barlow to a 9mm ortho, 10mm plossl and 6mm radian,.

I used 100mm F5 & F6.5 achromatic refractors during the bright daylight, yesterday. The CA was certainly less (actually much less) with the F6.5 scope than the F5. However, the F5 did not magically start to perform like a F10, or even outperform the F6.5 scope with the insertion of a barlow.

I also tried using a lowly performing 20mm Huygenian EP. Again, the barlow caused no magical improvement in the image; just more magnification.

This result is not what I would expect when I read the literature on these matters, but is inline with my observing experiences over many years.
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