Your problem could be from your choice of eyepieces. Zoom eyepieces are not a good choice for reasonably fast (f4.5-f5) systems. The 2.5 mm will also not be very useful as this is way to much magnification except under really perfect conditions. Try getting a good 25 mm Plossel (50X) and a good 2X Barlow (100X). The zoom will work much better with the Barlow as the light cone is narrower and the 2.5 mm may even be useable on occassion. Do make sure that the system is well collimated too as this can affect the performance.