Starkler
29-09-2006, 06:38 PM
I see in various threads people worrying about heavy eyepieces etc upsetting the balance of their dobsonian. Some suggest mods like adding felt to bear against the altitude hubs to increase the friction.
After having my gso dob for three years I have finally come to a point where I can say that I'm happy with the way that the scope moves. Movements should be light and with friction closely matching "sticktion".
This makes tracking objects at high powers a breeze, instead of the jerky frustrating experience you get with the scope as it comes from the shop.
I firmly believe that the tension spring arrangement on gso dobs doesn't help the altitude movement one bit! They rely on excess friction as a band-aid solution to the real problem, which is poor balance.
The scope moves much more nicely if the altitude springs are not used, but then there can be balance issues to contend with, especially if you done mods to make the altitude hubs more slippery, as I have by wrapping ebony star strips around them.
I solved the balance problem with 2x 1kg rectangular lead divers weights strapped to the rear of the scope. This overweights the rear end and I counterbalance this with a large speaker magnet that I stick on the tube at the viewing end. Adjusting balance at the viewing end makes life much easier :)
The result is that I have the magnet on near the top when using lightweight eyepieces such as plossls, and I lift it off and sit it near the alt hubs when I pop in the 31mm nagler.
No other counterweight scheme could be quicker or simpler to adjust, and I always get nicely balanced low friction/stiction movement regardless of the eyepiece I chose to pop into the focuser :D
Photos:
Black felt covered magnet on top of tube, lead weights strapped to rear.
Rear view showing weights strapped at 4 and 8 o'clock to miss rocker box
Ebony star on alt hubs . Alt springs only attached during transport
After having my gso dob for three years I have finally come to a point where I can say that I'm happy with the way that the scope moves. Movements should be light and with friction closely matching "sticktion".
This makes tracking objects at high powers a breeze, instead of the jerky frustrating experience you get with the scope as it comes from the shop.
I firmly believe that the tension spring arrangement on gso dobs doesn't help the altitude movement one bit! They rely on excess friction as a band-aid solution to the real problem, which is poor balance.
The scope moves much more nicely if the altitude springs are not used, but then there can be balance issues to contend with, especially if you done mods to make the altitude hubs more slippery, as I have by wrapping ebony star strips around them.
I solved the balance problem with 2x 1kg rectangular lead divers weights strapped to the rear of the scope. This overweights the rear end and I counterbalance this with a large speaker magnet that I stick on the tube at the viewing end. Adjusting balance at the viewing end makes life much easier :)
The result is that I have the magnet on near the top when using lightweight eyepieces such as plossls, and I lift it off and sit it near the alt hubs when I pop in the 31mm nagler.
No other counterweight scheme could be quicker or simpler to adjust, and I always get nicely balanced low friction/stiction movement regardless of the eyepiece I chose to pop into the focuser :D
Photos:
Black felt covered magnet on top of tube, lead weights strapped to rear.
Rear view showing weights strapped at 4 and 8 o'clock to miss rocker box
Ebony star on alt hubs . Alt springs only attached during transport