I have a laser pointer with a diffraction grating lens that creates a cross-hair, like the one seen below. enter image description here

I'd like to be able to increase or decrease the size of the cross-hair so that it may remain the same size when the laser is pointing at objects at different distances. I'm thinking that the best way to do this would be with a zoom lens, like what you would use with a digital camera. Would that increase/decrease the size with the zoom, or is there an easier way to do this?

To better convey what I'm trying to do: enter image description here

I want the crosshair size to remain the same, despite the distance of where the laser terminates.


1 Answer 1


place a convex lens in a way that the focal point is on the mouth of the laser pointer. so that the width of the light beam and therefore the size of the cross will remain fixed.



the led resembles the opening of the laser through which light comes out.

  • $\begingroup$ What you describe is in fact a telecentric lens. Such lenses have a field of depth for usual 5 by 20 mm. So in practice maybe you get the same size of the pattern, but it will be not sharp in most the distances. $\endgroup$ Dec 10, 2015 at 21:33
  • $\begingroup$ The application doesn't currently require it to be a sharp output. Will this allow me to change the output size by changing the distance away from the lense? $\endgroup$
    – Sam W
    Dec 10, 2015 at 21:59
  • $\begingroup$ en.wikipedia.org/wiki/Telecentric_lens $\endgroup$ Dec 11, 2015 at 4:11

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