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<blockquote data-quote="a33" data-source="post: 970243" data-attributes="member: 332642">So the relevant question here is, if I understand [USER=319227]@davemurgtroyd[/USER] right (which is not easy!): Does a flat mirror on the rim of a 'parabolic cut' reflect rays from the direction of the focal point in a different direction than the parabolic mirror itself?That is what dave doubts, he thinks the rays from the parabolic mirror would be aiming higher, if I read correctly.Turning it around for explanation reasons:Rays from the satellite on the flat mirror would reflect in the direction of the focal point, dave agrees on that.For rays from the satellite on the parabolic mirror, the question is: from what point of the dish can we determine in what main direction they reflect?- From the center of the dish, point E (or E2) on the drawing of message #11? No.- From the point where the rays through the center E reach the dish, point E1? (E1 being at the bottom side of the dish, then, opposite to the drawing.) No.- From the deepest point of the dish? YES. The parabolic form dictates what ray determines the main direction of reflection; in an offset dish that is not the central ray, but the ray to the deepest point.Where is the deepest point? It is not pointed out in the drawing at #11, but it lies even further away from center (E2) than E1, if I recall correctly; and I would have to lookup its position relative to the G-spot.What would be the reflecting angle at the deepest point? At the deepest point the 'tangent line' is by definition parallel tot the rim. So the reflecting surface would be parallel to the flat mirror on the rim.As the reflecting point is nearer to the main axis of the mother prime focus dish, however, the reflecting angle will be smaller at that point! And the parabola will be thus reflecting the ray exactly in the focal point again.&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;&nbsp; <img src="data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7" class="smilie smilie--sprite smilie--sprite18" alt=":-biglaugh" title="bounce laugh&nbsp; &nbsp; :-biglaugh" loading="lazy" data-shortname=":-biglaugh" />So: reflecting angle for a flat mirror on the rim of a parabolic dish is the same as for the parabolic mirror itself. And this applies for rays in both directions. QED.&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; <img src="data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7" class="smilie smilie--sprite smilie--sprite42" alt="M:W" title="xMexican Wave&nbsp; &nbsp; M:W" loading="lazy" data-shortname="M:W" />Greetz,A33</blockquote>

[QUOTE="a33, post: 970243, member: 332642"] So the relevant question here is, if I understand [USER=319227]@davemurgtroyd[/USER] right (which is not easy!): Does a flat mirror on the rim of a 'parabolic cut' reflect rays from the direction of the focal point in a different direction than the parabolic mirror itself? That is what dave doubts, he thinks the rays from the parabolic mirror would be aiming higher, if I read correctly. Turning it around for explanation reasons: Rays from the satellite on the flat mirror would reflect in the direction of the focal point, dave agrees on that. For rays from the satellite on the parabolic mirror, the question is: from what point of the dish can we determine in what main direction they reflect? - From the center of the dish, point E (or E2) on the drawing of message #11? No. - From the point where the rays through the center E reach the dish, point E1? (E1 being at the bottom side of the dish, then, opposite to the drawing.) No. - From the deepest point of the dish? YES. The parabolic form dictates what ray determines the main direction of reflection; in an offset dish that is [U]not[/U] the central ray, but the ray to the deepest point. Where is the deepest point? It is not pointed out in the drawing at #11, but it lies even further away from center (E2) than E1, if I recall correctly; and I would have to lookup its position relative to the G-spot. What would be the reflecting angle at the deepest point? At the deepest point the 'tangent line' is by definition parallel tot the rim. So the reflecting surface would be parallel to the flat mirror on the rim. As the reflecting point is nearer to the main axis of the mother prime focus dish, however, the reflecting angle will be smaller at that point! And the parabola will be thus reflecting the ray exactly in the focal point again. :-biglaugh So: reflecting angle for a flat mirror on the rim of a parabolic dish [B]is the same[/B] as for the parabolic mirror itself. And this applies for rays in both directions. QED. M:W Greetz, A33 [/QUOTE]

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