Here is an example of why accuracy is only meaningful if it's repeatable, and why the photos are 1000x more important and difficult to do than the measurements. The area that we're measuring is really, really small. This is what the area that I'm working with looks like when I'm working with it in image J. All of the measurements revolve around the edge of the blade, but the edge of the blade is not in the focal plane of the photo, so it kind of vanishes into a haze of pixels. I'm just guessing where it is. The better the focus, the better the measurement.
The problem is depth of focus. The edge of the razor and the edge of the razor blade are not on the same plane. The edge of the razor blade 2.00mm lower than the edge of the razor. The depth of focus of the Pluggable USB 2.0 is only 0.10mm. Put differently, there is a 2,000% disparity between the depth of focus of the camera is capable of and the 2 focal planes of interest (side of the razor, and side of the blade).
The only solution to this problem in 1 picture is to painstaking find the point where these two features are both simultaneously in the best focus together. Basically we're finding the focal point right in the middle, where we are 1.00mm distant from these two features. That's extremely hard to do.
The solution is to take 2 pictures, without moving the camera. The first picture focuses as clearly as possible on the side of the razor blade in the crispest detail possible. The side of the razor will be very blurry in this shot. The second picture is taken without moving the camera, and the focus is adjusted to get the crispest image of the side of the razor where the shave-plane is defined. In this picture, the blade will be a blurry.
The next step is focus stacking. We take both photos, and use software to combine them such that it borrows the best "in-focus" part of both photographs, at every point on both photographs, to create a new photograph where everything is in focus at the same time.
Here is a fantastic 5 minute video that explains it much better. It's actually pretty easy to do.
The problem is depth of focus. The edge of the razor and the edge of the razor blade are not on the same plane. The edge of the razor blade 2.00mm lower than the edge of the razor. The depth of focus of the Pluggable USB 2.0 is only 0.10mm. Put differently, there is a 2,000% disparity between the depth of focus of the camera is capable of and the 2 focal planes of interest (side of the razor, and side of the blade).
The only solution to this problem in 1 picture is to painstaking find the point where these two features are both simultaneously in the best focus together. Basically we're finding the focal point right in the middle, where we are 1.00mm distant from these two features. That's extremely hard to do.
The solution is to take 2 pictures, without moving the camera. The first picture focuses as clearly as possible on the side of the razor blade in the crispest detail possible. The side of the razor will be very blurry in this shot. The second picture is taken without moving the camera, and the focus is adjusted to get the crispest image of the side of the razor where the shave-plane is defined. In this picture, the blade will be a blurry.
The next step is focus stacking. We take both photos, and use software to combine them such that it borrows the best "in-focus" part of both photographs, at every point on both photographs, to create a new photograph where everything is in focus at the same time.
Here is a fantastic 5 minute video that explains it much better. It's actually pretty easy to do.