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dac_experiments:geometry
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dac_experiments:geometry [2019/05/08 14:56] matthias |
dac_experiments:geometry [2019/06/07 15:01] (current) matthias [Example: How to find out my own O-matrix] |
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| {{ :processing:dacgeometry_experiment.jpg?nolink&400 |}} | {{ :processing:dacgeometry_experiment.jpg?nolink&400 |}} | ||
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| + | Fig. 1: Experimental setup | ||
| More precise and detailed calculations are available in this file, extracted from the fable project: {{ :processing:fable_geometry_version_1.0.8.pdf |}}. | More precise and detailed calculations are available in this file, extracted from the fable project: {{ :processing:fable_geometry_version_1.0.8.pdf |}}. | ||
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| Here is an example, taken from an old Fable manual (Note: one of the example is wrong, I did see that some times ago, seb) | Here is an example, taken from an old Fable manual (Note: one of the example is wrong, I did see that some times ago, seb) | ||
| - | {{ :processing:fableimageorientexample.jpg?nolink&400 |}} | + | {{ :processing:fableimageorientexample.jpg?nolink&400 |Fig. 2: Example for the 8 possible orientations of a 2D image}} |
| + | |||
| + | Fig. 2: Example for the 8 possible orientations of a 2D image. | ||
| Again, more precise definitions and calculations can be found in a former Fable manual: {{ :processing:fableimageorientdoc_0.5.pdf |}} | Again, more precise definitions and calculations can be found in a former Fable manual: {{ :processing:fableimageorientdoc_0.5.pdf |}} | ||
| - | ===== Example ===== | + | ===== Example: How to find out my own O-matrix ===== |
| Let's assume our sample is rotated from ω1 = -20° to ω2 = +20° during the acquisition. When you reach extreme ω values you can see a shadow on one side of the diffraction images. These shadows originate from the DAC which has a limited opening angle on the outside. The further you rotate, the less 2θ angles are visible. | Let's assume our sample is rotated from ω1 = -20° to ω2 = +20° during the acquisition. When you reach extreme ω values you can see a shadow on one side of the diffraction images. These shadows originate from the DAC which has a limited opening angle on the outside. The further you rotate, the less 2θ angles are visible. | ||
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| Let's do it for the image at ω1 = -20° | Let's do it for the image at ω1 = -20° | ||
| + | |||
| + | {{ :dac_experiments:orientations.png?600 |Fig. 3: Example for different orientations of the same image}} | ||
| + | |||
| + | Fig. 3: Example for different orientations of the same image. | ||
| === Step 1 === | === Step 1 === | ||
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| Ask the beamline scientist if the images are saved in a different orientation than the actual setup geometry. | Ask the beamline scientist if the images are saved in a different orientation than the actual setup geometry. | ||
| - | If this is not the case and the diffraction image on the screen is the same as the one you would see when we had a photofilm, everything is fine. If this is the case, you have to keep it in mind for the following steps. | + | If this is not the case and the diffraction image on the screen is the same as the one you would see when you had a photofilm, everything is fine. But if it is the case, it makes it more complicated. You have to keep it in mind for the following steps. |
| === Step 2 === | === Step 2 === | ||
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| Have a look at the sample stage. In which orientation is the rotation taking place? Where is the rotation axis pointing? | Have a look at the sample stage. In which orientation is the rotation taking place? Where is the rotation axis pointing? | ||
| - | I guess in most setups the rotation axis of ω is pointing to the top or to the bottom (see figure 1). Other directions just make no sense. From this you can conclude that the shadow in our diffraction image has to be either on the right or on the left side of the image. With this information you can already exclude 4 out of the 8 possible orientations. | + | I guess in most setups the rotation axis of ω is pointing to the top or to the bottom (like the Z-direction in figure 1). From this you can conclude that the shadow in our diffraction image has to be either on the right or on the left side of the image. With this information you can already exclude 4 out of the 8 possible orientations. |
| === Step 3 === | === Step 3 === | ||
| - | Watch the sample stage carefully while it is rotating. Is it rotating clockwise or counterclockwise during the image acquisition? | + | Look for the beamstop in the experimental setup. Where is it coming from? Where should it be in the image? |
| - | Let's assume we observe that it is rotated **counterclockwise** when we look at it from top. This means that the image at ω1 = -20° should see a shadow on the left side. Think about it carefully and try to follow and understand this conclusion. | + | For this example, let's assume it comes **from top**. Knowing where the beamstop is located, you can exclude two more possible orientations. |
| === Step 4 === | === Step 4 === | ||
| - | After excluding another two of the possible orientations, we are left with only two possibilities. To find out the right one, you can compare your image with a still image which you took before or afterwards. Are there any features which are remarkable, such as a broken pixel on the detector or any other feature which you can see in every image? You can also compare the image at ω = 0° to see if there are recognizable diamond spots. | + | Watch the sample stage carefully while it is rotating. Is it rotating clockwise or counterclockwise during the image acquisition? |
| + | |||
| + | Let's assume we observe that it is rotated **counterclockwise** when we look at it from top. This means that the image at ω1 = -20° should see a shadow on the left side. Think about it carefully and try to follow and understand this conclusion. | ||
| + | |||
| + | === Conclusion === | ||
| - | If you find something like this, you are lucky. In the example | + | If you have followed the example in the right way, you should have come up with the solution that Orientation #8 is the correct one (corresponds to O-matrix [0,-1,-1,0]). |
dac_experiments/geometry.1557327387.txt.gz · Last modified: 2019/05/08 14:56 by matthias
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