There's a good description of the maths of the balancing process here:
http://www.lcas-astronomy.org/articl...ry=accessories
On a German equatorial mount, how large a counterweight (c/w) will you need for a given telescope weight and where should it be placed? The formula is:
(Scope weight) x (scope-to-mount distance) / (c/w weight) = c/w-to-mount distance
A heavier counterweight will need to be further up the shaft than a lighter counterweight to achieve the same balance. There is also the advantage that the higher up the shaft the counterweight is, the less vibration you will tend to get from the "pendulum effect" of the hanging mass of the counterweight on the shaft. But you need to remember that there is a limit to how close to the pivot axis you can get the counterweight, so if the counterweight is too heavy for the OTA, it may not be possible to get it close enough to the pivot axis to get the telescope balanced at all.
You could start by weighing your OTA in its minimum and maximum configurations (i.e. eyepiece only, and with your heaviest camera / filter wheel etc in place), and also measure the minimum and maximum radius of the counterweight from the pivot axis. This should then give you an idea of the optimum counterweight mass for your scope - 5 kg may be better than 4 kg, but 4 kg plus 5 kg may be too much.
Remember that on a Newt, heavy accessories such as cameras and filter wheels are positioned further from the pivot axis than the OTA itself, so the calculation should be something like:
(Weight of OTA x Distance of OTA from pivot axis) + (Weight of camera x distance of camera from pivot axis) + ...
Even if you added cameras, finderscope, upgraded focuser, additional wiring, guidescope etc it would still be fine.
