Optica b/c 3X Barlow (1.25).

I picked up a Criterion Refractor and in the box was an Optica b/c 3X Barlow (1.25). I have seen the 2X Optica barlows before but never a 3x. I can find nothing about it online. There is a copy of Optica's 1978 line on the internet but nothing about a 3x Barlow. I did a side by side with my TV 2.5 (C8)and was pretty surprised. Anyone have any info on it or can point me in the right direction? I dont need another barlow but I have never had a 3x before thanks chuck

Like most such suppliers, Optica b/c was an importer, not a manufacturer. Typically this may have been mfg by Circle-Tee or other Japanese mfg; look for a possible stamping on the side to indicate mfg. Any given Barlows' magnification is determined by it's negative focal length & distance lens is placed in front of an eyepiece (vary that length & vary the magnification factor). Fixed-power Barlows typicaly require an eyepieces' focal plane be placed at or very near the top of the Barlow housing in order to achieve the stated magnification (other placement results in other magnification, a spacer tube will result in greater magnification same as placing a Barlow in front of a Star diagonal vs after).