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The lens zooms and focuses something very far away, yet the reticle inside the lens assembly is in perfect focus just like the far objects. How?

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    $\begingroup$ For personal reasons, what scope is that? I like the BDC Markings. $\endgroup$ – UIDAlexD Jul 2 '18 at 19:48
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    $\begingroup$ @UIDAlexD That’s a Leupold Mark 8 with H-27D illuminated reticle. $\endgroup$ – canadianer Jul 2 '18 at 22:16
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The image of the distant object is formed in the plane of the graticule.
The eyepiece is then focused on the image of the distant object and the graticule which is in the same plane.

enter image description here.

The objective forms an inverted image of the distant object in its focal plane.
The next lens combination forms an erect image in the plane of the graticule (reticle in North America).
That image of the distant object and the graticule are focussed by the eyepiece so that the eye sees the distant object and the graticule both in focus.

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  • $\begingroup$ Great. Seems like the same approach can be used to cut a collimated beam into half or a custom shape with sharp edges by using a sharp stencil (reticle) and not get the feathered beam edge issue caused by diffraction? $\endgroup$ – Mark Legault Jul 2 '18 at 13:56
  • $\begingroup$ can this method be used to sharply cut a projection beam with a stencil? $\endgroup$ – Mark Legault Jul 2 '18 at 21:33
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    $\begingroup$ Perhaps you could also touch on first focal plane reticles. $\endgroup$ – canadianer Jul 2 '18 at 21:56
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    $\begingroup$ @canadianer a FFP scope puts the reticle on teh same plane as the target, which means with variable powers of magnification the subtension of the reticle over the target stays the same. Comes in handy with mildot scopes, since with a FFP scope the reticle stays the same relative size to the target when zoomed in, so if a dot covers 1mil when the scope is at 10x, it will still cover 1mil of the target when zoomed out to 2x or in to 20x. Check out primalrights.com/library/articles/… $\endgroup$ – ivanivan Jul 2 '18 at 23:10

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