Quote:
Originally Posted by multiweb
Just one more question(s) Stefan, then I'll leave you alone 
Is the rotational aspect important when stacking small lenses like it is for bigger surfaces like mirrors in a folded light path and what is achieved by rotating optical components on their axis? I read it can add up or cancel errors. Is that all it is and does it make a big difference in your opinion or it doesn't really matter? Is that something you test when you do the final assembly with your mirrors? |
In an optical train every element has a tilt error (and other errors too), simply because nothing can be made absolutely perfect, and tilt errors cause astigmatism, therefore by rotating various elements relative to each other, it is possible, sometimes, to minimise astigmatism. But that only works if the effects of individual errors have similar values. For example, tilt errors in a field corrector may be able to compensate to some extent the residual astigmatism of a primary or secondary mirror in a cassegrain system.
To answer your question: It all depends on how accurate the optical components have been manufactured and mounted. It is possible to keep the errors small enough so that rotating elements won't make any difference. That is what I aim for. After I assembled my field corrector, I screwed it into a jig on the lathe and looked at the reflections of a laser beam while it was spinning. The reflected spots, projected onto a surface some distance away, showed little wobble, so I'm confident that it will be ok.