Barlow question

I'm not sure that this is the right forum, if not I apologize. Anyway, I just bought a Celestron 2x Shorty Ultima barlow. To my amazement when I put it in my C8 with my CCD the final F/R came out at F/25, or the barlow was acting like a 2.5x barlow. I bought the 2x barlow to be a 2x amplification, I already have a 2.5x Powermate and 3x Televue. I wanted the 2x for imaging on a smaller scale. I am wondering of anyone else has seen this and if there is some kind of a workaround.

Thanks a bunch!!
Paul Maxson

Yes, Chris is correct, although my recollection from testing years ago was a range of 2.1x to 2.4x, with an average probably around 2.2x, depending on spacing to the field stop of the eyepiece. The only half-way reasonable workaround I can think of is to find a way to move the Barlow lenses closer to the CCD chip, perhaps by unscrewing the silver barrel from the black eyepiece holder and instead of the black eyepiece holder using a section of 1.25" ID pipe with set screws at each end that will allow you to control the spacing between the chip and the Barlow lenses.
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Mike