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I am trying to take pictures of a fluid interface touching a thin plate. This plate is 0.01 inch thick and 3 inches wide. I've included a sample image below.

Is there a good way to align my camera so that it looks at the thin edge of the plate dead on? I have managed to get close through trial and error but I don't really have a systematic way of doing it.

enter image description here

  • Are you measuring the meniscus of various fluids? – Stan Apr 10 '18 at 19:16
  • @stan yes, I'm trying to measure the contact angle – Ragnar Apr 10 '18 at 21:24
  • Don't forget that the plate must be vertical and perpendicular to the surface of the liquid. You did not specify perpendicularity which will affect your analysis – Stan Apr 10 '18 at 22:58
  • Anyone have suggestions for tags for this question? image-alignment is about aligning multiple images for stacking or panoramic photographs... – Please Read Profile Apr 10 '18 at 23:17
  • @Stan The plate is suspended on a hinge so that gravity should ensure that it is perpendicular to the surface of the liquid – Ragnar Apr 11 '18 at 14:08
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There are a couple of things you can try.

  1. Shine green light on one side of the plate and red on the other. When viewed from the edge-on, there will be none of the red or green visible from either of the sides. As a benefit, the predominating colour will indicate which direction to move the camera.
  2. Using an interference pattern such as a moiré or speckle from a laser source. As you view the edge, the speckle pattern will become more coarse as you resolve the edge.
  • Thanks, I will try shining the two colored lights on either side – Ragnar Apr 11 '18 at 14:09
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A set of inexpensive macro focus rails will let you make fine left/right and forward/backward adjustments to the camera position. You'll still need to get the optical axis parallel with the plate, probably by loosing the mounting screw a bit and adjusting the camera. Once you've got it once, though, you can lock it down and use the rail adjustments to line the camera up laterally.

Also, using a longer lens will let you put the camera farther away. More distance means that you'll need to move the camera a greater linear distance for a given angular change, so adjustments don't have to be so precise. If you're using a 60mm macro lens, switching up to 100mm or 180mm will give you two or three times the distance, which should help make alignment easier. (And at 180mm and 1:1 magnification, you'll still only be ~18" from the subject.)

  • Thanks, I'll take a look. Although as you mentioned, hardest part is getting the axis parallel to the plate. I will probably try and use a macro stage and the techniques described by Stan – Ragnar Apr 11 '18 at 14:29
  • @MrZ. Using a longer lens may help -- I've added that above. – Caleb Apr 11 '18 at 14:45
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I would try putting a flshlight behind the plate (if thats possible) and aligning the shadow on the center of your lense. This might work.

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