Typical Calibration Measurements
Near field calibration images are taken using one of three targets, a NBS 1952 Resolution Test, 10 LP/mm Ronchi Ruling, or 1951 USAF Resolution Test Targets. The resolution test targets have three bars and the Ronchi Ruling has a 1D pattern of bars. The calibration is determined from the three bar targets by measuring the distance in pixels between all four sets of neighboring rising edges and neighboring falling edges. The standard deviation in the calibration is measured from the different values found from the four sets.
The intersects with the rising or falling edges are calculated with a threshold value. The threshold is typically scanned to ensure it does not significantly impact the calibration. Ideally, the calibration target is horizontal or vertical in the image. If not, the image is rotated before calculating the calibration. The image rotation is scanned to verify the bars are horizontal or vertical.
Figures show the region used for calibration, the rising and falling edge intercepts, and the variation in calibration with threshold and angle (dotted lines are standard deviation from the different edges).
| Camera | Last Calibration | Calibration Current? |
|---|---|---|
| S20 Regen Out | 1/22/2024 |  |
| S20 Pulse Picker | 1/22/2024 | |
| S20 Preamp Near | 1/22/2024 | |
| S20 Preamp Far | 1/22/2024 | |
| DM Near | 8/18/2023 | |
| DM Far |  | |
| Inj Near | 8/17/2023 | |
| Inj Far | | |
| Comp Near | | |
| Comp Far | | |
| PB Near | 9/20/2023 | |
| PB Far | |
Figure 1: NBS 1952 Resolution Test Target, the bars near the Thorlabs logo are 0.48 LP/mm.
Figure 2: Calibration test target with a row of uniformly spaced bars.
Figure 3: 1951 USAF resolution test target.