ok just looked it up.... its f/4.
*a 30mm for low power
*a 6 or 7mm for planets/highpower ( you could go lower but one has to take into acount eye relief). 7 mm gives you 114x magnification approx
*a 15 to 20mm for medium...
a barlow and a 7mm will give you 228x and you probably wont need to go higher
