ZF 41 scopes

[gj.atkins]

Would anybody have to hand or know where I could a diagram of the optical set up for these orrible scopes. I have stripped one down to clean the lens elements but on reassembly the image is not "flat." I am sure there is some lens round the wrong way or something. I am waking up in the night in a sweat about it!

Information

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[Calif-Steve]

Where are you located? Try Parsons Scope Service in Oregon. Good luck on this one, it will be tough.

[Patrick Chadwick]

John, I know sweet FA about Z41 scopes, but there is a general rule (well, OK, trend) for optical setups that may help you to eliminate a few possibilites. The designer will probably have laid out the surfaces so that the angle of the light on the surface is roughly equal on both sides. This is to reduce light losses through internal and external reflection and to reduce spherical aberration. To illustrate what I mean, consider a simple lens with parallel light coming in from the left, and being focussed to a point, i.e. converging, on the right. The (I or I) combination indicates a plano-convex lens, i.e. flat on one side, as that is easy to represent with keyboards symbols. In real life it will be more difficult, and you have to judge which side is the more strongly curved.

So for a simple telescope objective:
Parallel light ----(I ----converging is more plausible.
Parallel light-----I) ----converging is less plausible.
Why? because the angle of emergence in the second example will cause more light loss through internal reflection than is saved by the zero incidence angle on the "input" side. It will also be worse for spherical aberration (if my memory serves me right).

Likewise, if you look at a microsope objective, you will see:
object-----I)------internal optics
rather than
object-----(I-----internal optics.

So if, for instance, you have dismantled an eyepiece and are puzzled how to assemble the elements, then ----I)---(I---- is more likely than -----(I---I)---- But I stress that this is not a hard and fast rule. Doublet and triplet lenses can be very confusing. Nevertheless it may help you to get enough definitely right that you only have to try a couple of options to find the correct setup.

If you didn't clean the lenses too hard at the edges, marks left by the retaining rings may also be a clue to correct assembly.

Failing a drawing, this tip may help.

Patrick

P.S: applying the above to a telephoto lens, means that
(distant object) parallel --------(I--------I(------ is likely
but
(distant object) parallel --------(I--------)I------ is unlikely