Yep that's the manual. Mine is the 90mm version, and it says that you need the diagonal, which makes sense, since there is no place to attach eyepieces. I have a 3x Barlow lens, a 25mm, a 12.5mm, and a 4mm. I measured the parts on the telescope, and it looks like all the fittings are for 1.25" pieces so I was thinking of buying this diagonal. Tell me what you think. And thanks for the tip on the cleaning :)