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Using focus position as a Z location

afotion
Hey all,

I have a simple one for you which may have some complex answers. As a rule of thumb I have always avoided using any kind of focus points/positions to do any kind of Z location/height measurements.

Do any of you use focus points with high confidence? I have had decent experiences and sometimes I have had complete failures with it. Is it safe to assume it comes down to material and lighting and the application? I found that when trying to perform this on a very centralized locations within your FOV it then becomes very difficult to make repeatable.

I would love to hear your thoughts.

Thanks!
Parents
  • The focus postion depends on the size of the target.
    I think it calculates the position on an average of net pixels in the target area. If the defect is narrow, or with a V form, I think you can't measure accurately the depth.
    You can try to do it by comparison with the profilometer, and find the right parameters, but if your supplier change the color of the material, or the surface treatment, the result won't be valid !!!!!
    What i said about 0.01 mm was the repeatabilty range of focus on 10 measurements, compared to a contact measured plane.
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  • The focus postion depends on the size of the target.
    I think it calculates the position on an average of net pixels in the target area. If the defect is narrow, or with a V form, I think you can't measure accurately the depth.
    You can try to do it by comparison with the profilometer, and find the right parameters, but if your supplier change the color of the material, or the surface treatment, the result won't be valid !!!!!
    What i said about 0.01 mm was the repeatabilty range of focus on 10 measurements, compared to a contact measured plane.
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