Finder parallax

[Ally8446]

Could someone do their best to explain if a Telrad or Rigel finders suffer from parallax, and if not then why not ?

[umadog]

There is basically no parallax because the rings are projected at infinity. In other words, the light rays from the rings are parallel (not converging or diverging). This is achieved by placing the target to be projected (reticle) at one focal length from a lens. That's why there's so much empty space in a Telrad. You can see the effect here: http://en.wikipedia.org/wiki/Reflector_sight

If you scroll down on the wikipedia page you will see some ray diagrams. The Telrad is design (1). I would guess most other finders you see are design (2), since there is no lens between the reticle and the glass screen. This would also explain why they coat the glass on those finders in a funny way. I've not looked at my own little RDF carefully enough to see how the glass works to project the reticle. I guess it must indeed be curved, as shown in the figure. Must take a look! Thanks for the question!