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HI
I am currently playing with imaging device that would take pictures of the content of the bottom of the small plastic container. The container is just a tube of 7mm in diameter. When I image an empty tube I get a proper high contrast image of the dust on the bottom of it. However the problem is that I have to take pictures of targets in liquid.
The device has a camera, a lens with 1x magnification (sufficient for the resolution and the target I am trying to image. The problem is the illuminations. I have build a 4f Koehler illumination for the this purpose and it seems to be working fine. When I test the beam of light coming out of it I get mostly parallel beam of light, slightly diverging but not much. When I use that system to image the bottom of the plastic container I get a proper, decent high contrast image of the dust on the bottom of it. The problem starts when I add liquid into it. The content of the container is no longer evenly illuminated, even though the light outside of it seems to be ok. The effect is that the edges of the container (which is circle) are darker and seems to be slightly out of focus in comparison to the center. The effect is magnified if there is very little liquid added and gradually disappears the more liquid I add (however never getting even close to the picture of the empty container). Clearly the top surface of the water is acting as a lens due to it's meniscus. I tried all sorts of ways to try to mitigate that but with no success and sadly for a good pictures I need even illumination across the entire picture. Small variations I guess would be fine but not more than few percent.
Any ideas how to mitigate this issue in the optical design? How to even measure if this lens made by the water surface is going to be convex or concave?
Any help is very much appreciated.
Many thanks.
I am currently playing with imaging device that would take pictures of the content of the bottom of the small plastic container. The container is just a tube of 7mm in diameter. When I image an empty tube I get a proper high contrast image of the dust on the bottom of it. However the problem is that I have to take pictures of targets in liquid.
The device has a camera, a lens with 1x magnification (sufficient for the resolution and the target I am trying to image. The problem is the illuminations. I have build a 4f Koehler illumination for the this purpose and it seems to be working fine. When I test the beam of light coming out of it I get mostly parallel beam of light, slightly diverging but not much. When I use that system to image the bottom of the plastic container I get a proper, decent high contrast image of the dust on the bottom of it. The problem starts when I add liquid into it. The content of the container is no longer evenly illuminated, even though the light outside of it seems to be ok. The effect is that the edges of the container (which is circle) are darker and seems to be slightly out of focus in comparison to the center. The effect is magnified if there is very little liquid added and gradually disappears the more liquid I add (however never getting even close to the picture of the empty container). Clearly the top surface of the water is acting as a lens due to it's meniscus. I tried all sorts of ways to try to mitigate that but with no success and sadly for a good pictures I need even illumination across the entire picture. Small variations I guess would be fine but not more than few percent.
Any ideas how to mitigate this issue in the optical design? How to even measure if this lens made by the water surface is going to be convex or concave?
Any help is very much appreciated.
Many thanks.
