A flat piece of heat-absorbing glass is often placed in the light path between the condensing lens and the slide, to avoid damaging the latter.
2.
The reticle collimation optics are situated at 90?to the optical path making lighting difficult, usually needing additional electric illumination, condensing lenses, etc . A more compact type replaces the lens / beam splitter configuration with a half silvered or red dot type used on small arms.
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