# A question about different lens setups imaging a rotating stick

roineust
If i put a rotating stick behind lens of several types, so the stick center is behind the lens center, will the stick edges always appear to move at the same rate as areas closer to the stick center?

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If i put a rotating stick behind lens of several types,
Any possible lens?

so the stick center is behind the lens center, will always the stick edges appear to move at the same rate as areas closer to the stick center?
What is "rate"? Angular velocity? Instantaneous or average over a cycle?

roineust
roineust
Any possible lens?

What is "rate"? Angular velocity? Instantaneous or average over a cycle?

What is the case for all the options that you have mentioned for main common types of lenses?

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Mentor
I think he is trying to get you to make a better question, not volunteering to do it for you.

roineust
What is the case for all the options that you have mentioned and for all main different types of lenses?

By rate i mean, if there is always a straight line between the stick edge and the stick center.

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roineust
What is the case for all the options that you have mentioned and for all main different types of lenses?

I think i recall from visual memory, that for a certain lens type, if you look from the side of the lens at the stick, you will see the stick as a curved line and more curved as the stick gets closer to the lens edge, even if the stick is not rotating, is that correct?

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... even if the stick is not rotating...
So what's the point of the rotation?

roineust
roineust
So what's the point of the rotation?

Correct, my question is also about the rate: Does there exist a common lens type, in which the stick seems to be curved toward the edges when the stick is not rotating and/or seems to be more/same curved toward the edges as a result of rotation, be it when looking from the side or from the center axis?

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Correct, my question is also about the rate: Does there exist a lens type, in which not only the stick does not appear to be straight, but it even seems to be more curved at the edge, as a result of rotation, be it when looking from the side or from the center axis?
Do you mean more curved than when not rotating at the same orientation? Are you asking about signal delay of the light rays due to the optical density of glass?

roineust
roineust
Do you mean more curved than when not rotating at the same orientation? Are you asking about signal delay of the light rays due to the optical density of glass?

I am asking about such a phenomenon existence twice, once as a result of only the density of glass and again as a result of only the geometry of of the lens.

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I am asking about such a phenomenon existence twice, once as a result of only the density of glass and again as a result of only the geometry of the glass.
So no rotation then?

roineust
roineust
So no rotation then?

As a result of rotation and also when there is no rotation.

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As a result of rotation and also when there is no rotation.
You already know that lenses can distort things. The rotation can create distortion due to different light travel times from different parts of the stick. But these are tiny non-noticeable effects at non-relativistic speeds.

roineust
Gold Member
If i put a rotating stick behind lens of several types,
Here's another example of a question that's so open that it just can't be answered usefully. We all read it slightly differently and so we can all come up with different answers. Wouldn't a DIAGRAM or even a selection of ("several") diagrams help us all to be talking about the same thing that the OP had in mind?
For a start, what is the axis of rotation of the stick?

roineust
roineust
Here's another example of a question that's so open that it just can't be answered usefully. We all read it slightly differently and so we can all come up with different answers. Wouldn't a DIAGRAM or even a selection of ("several") diagrams help us all to be talking about the same thing that the OP had in mind?
For a start, what is the axis of rotation of the stick?

Here is a diagram and the question is if such a phenomenon happens in lens, first with no stick rotation and then with stick rotation. The apparent stick (in blue) is curved in one direction, but the question is about such a possible distortion, also in the opposite direction. The question is also about possible rate change, of the apparent stick curvature (a distortion that changes in time).

if such a phenomenon happens in lens, first with no stick rotation
Is the lens rotationally symmetrical around the view axis?

roineust
roineust
Is the lens rotationally symmetrical around the view axis?

Yes