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I'm working with an optical sensor which uses a PSD to measure distance. The sensor itself has a lens on the emitter and receiver part which i assume it uses to make it measure within a certain range. I want to put another lens on top of the receiver lens so that i can make the range smaller thus making it more accurate within that new range.

The thing is the datasheet does not tell me what the focal length or any other optical parameter of the lens is but i was able to calculate the angle at which the light beam would hit both sides of the PSD (So the angle it would have when it measures minima and maxima). my question is can i find the focal length and/or other optical parameters using just the transmission angle (Not sure if that is the right word).

https://docs.rs-online.com/8b00/0900766b80d1bdcd.pdf datasheet on the sensor

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It appears from the datasheet that this device calculates the object distance by measuring the angle (off-axis) of the image. This depends on calibrating the PSD, based on the focal length of its lens and the spatical separation between the receiver and transmitter optics (and of course that the transmitter is properly boresighted).

So, to decrease the sensing range you want to get a greater distance (from zero, on axis) of the image spot for the same object distance. This requires you to add a lens which produces a net focal length, including the existing optics, greater than at present. I think a simple raytrace will show the power of a negative lens you want, but you also have to consider the change in back focal distance, or your image won't be on the PSD and your results will be wrong. Assuming you can get the image on the PSD, then a careful calibration with known distance targets should suffice.

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Since the device claims to use triangulation to determine distance, I would suggest that you use a thin prism in front of the pickup in order to shorten the range. Then you would need a re-calibration table, graph, or function.

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  • $\begingroup$ Won't this just deflect, rather than magnify, the system? I thought the OP was looking for smaller range but higher precision. $\endgroup$
    – Carl Witthoft
    Commented May 17, 2021 at 18:58
  • $\begingroup$ I was thinking that, when he said that he wanted to make the range smaller, he wanted to bring it closer to the sensor. $\endgroup$
    – R.W. Bird
    Commented May 18, 2021 at 13:09

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