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Personally, and I know others have the exact opposite view, I have never had any joy using Barlows. The ones I have used have been good quality Televue ones, but never liked the view through them compared to a stand alone eyepiece.
Sorry to hear that you have an issue with the 15mm Superview. I have one and I think it is a little ripper for the price, it is my main ep in my 8" f4 dob. Little bit of barely noticeable field curvature but coma that one would expect in an f4 is not noticeable and the stars are pinpoints in the middle.
If buying eyepieces in person, I always (even with inexpensive ones) ask to see the eyepiece and check it for dust or particles before handing over my hard earned. Never had a problem yet, but always worth doing.
So your existing eyepieces will give
25mm - 26x with exit pupil of 5mm
10mm - 65x with exit pupil of 2mm
6.7mm - 97x with exit pupil of 1.34mm
If you barlow them you get
52x
130x
194x
To be honest, 97x is pushing this little scope to its limits, so the only useable power you will gain is 52x and you already have 65x, so I don't think it will be worth while IMHO.
I was not aware that either Televue or GSO made a 1.5x barlow?
Malcolm
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