How much collimation flex is there

One purpose of a telescope tube is to eliminate all flex so that when a telescope is collimated, it is collimated no matter where it points. However, I know that this can be a difficult job.

We just set up a newly reconstructed Truss tube dob. It is a 22 inch F 5.

When collimated in a down position (a few degrees above horizon), the laser spot is dead on. When you crank it up to zenith, the spot is maybe 1/8 inch from center.

I've inspected for the obvious things, mainly loose parts I suppose.

Is this within spec? Is there any margin for error? Is it a problem with big truss tube dobs?

What is your advice. And where should I look to make it better?

Alex

I get a little movement of the dot if I move the scope from horizontal to vertical. I might add up to 1/16" with my 15" Truss. I have checked several others and have seen some flexing in every one, with 1/16" to 1/8" being about the average. I have not personally checked one that had 0 movement. I have also checked several solid tubes and found they also had similar movement. Discovery solid Dobs can be flexed by just laying your hand on the end of the tube or pressing slightly with your hand.
I would say that it would be possible to eliminate this with larger truss tubes, but I don't find the amount of movement to be a problem.
As Rick stated, I always collimate my scope at a 45 degree angle. This divides the movement in half and seems to make it negligible as far as collimation is concerned.
Floyd