I have a SIGMA 105 macro lens, and bought the manual focus gearing so that I could install it into my housing.To my surprise I found there was a problem, when I tried to shift focus using the housing controls, rather than rotating the gearing, it was pushed aside against the lens body and refused to move,
My solution is the red band on this lens.
What's needed is something that will support the lens gearing at the point where the lens and housing gear teeth meet ensuring they "mesh" together properly but still allowing the lens gear to rotate.
If you have already read my previous post "Build your own lens gear" this item, that I'm calling a "slip ring" has been produced with some of the same materials. A piece of drainpipe was found that would just fit over the rear of the lens body and a cross-section was cut approximatly 10mm wide, the outer face is first covered with heavy duty VELCRO adhesive backed tape (the furry part). The bright red material is a lighter duty VELCRO tape with the "hook" part on one side, and the "furry" part on the other, it's usually marketed as a wiring tidyer, when you roll some wiring up, wrap one of these around one side and it will stick to itself. I chose this because the furry side feels more like the cloth on a pool table, As opposed to the "really hairy" heavy duty stuff.
The red VELCRO has been peeled back for this picture.
Wrap the lighter VELCRO over the outer surface of the ring, the hook side sticks readily to the heavy duty VELCRO already there, leaving the cloth side exposed. This is the side that will allow the lens gear to slide during rotation.
look carefully at the inner wall on the close-up picture of the slide ring, there is a groove filed into the wall. This is because SIGMA has a small focus limiter switch at the base of the lens, the groove allowes the slip ring to be fitted without disturbing the switch.
