Microscopy 101
In an optical microscope, magnification is a combination
of objective and eyepiece. For a microscope set up for imag- ing, it is a combination of the objective, C-mount, and cam- era pixel and sensor size that defines the field of view (FOV), magnification, and resolution at
the camera. Importantly,
Figure 1: Lateral piezoresponse force micrographs for a potassium-sodium ferroelectric film measured at different temperatures (a)–(d). Upon heating above 110°C, the periodic MC
domain structure vanishes until it reappears when
cooling down again. Image reproduced from [1], used under a Creative Com- mons Attribution (CC BY 4.0) license.
the limit on the dynamic range of the sensor. When putting together a dynamic imaging system, an expert supplier can help work through important considerations such as camera and microscope resolution, chip and pixel size, dynamic range, sensitivity, and frame rates.
the view through the microscope is typically circular, and any available camera sensor FOV is typically rectangular or square. Te result is that the camera FOV will never exactly match the full area possible on the microscope. It is com- mon practice to match the circular diameter of the micro- scope with the rectangular diameter of the camera sensor, so an 18.66 mm diagonal sensor would be used with a 19 mm diameter microscope FOV. A larger sensor camera could be used, but then there would be vignetting at the corners of the image, which is best avoided. Te eye/brain combination is very forgiving of this, but digital sensors can be very sensi- tive to such uneven illumination. It is also possible to image with camera sensors that are smaller than the maximum FOV of the microscope. In this case, the image FOV will be smaller than the maximum available microscope FOV. Tis will result in a higher-magnification image, however, there reaches a point where high magnification does not improve the resolution or increase the information in the image. Typically, this is compensated for by using C-mounts with additional optics to demagnify the resulting image. Tis is demonstrated in Figure 4. To ensure the best quality image without vignetting, typically the best solution is to choose a sensor and C-mount combination where the rectangular area of the sensor just fills the circular FOV of the microscope, as shown in Figure 4iii–4iv. Tis maximizes the final image size without having to crop out the vignette. Camera resolution is certainly a key parameter to con- sider in an imaging system but should not be taken as a
Figure 2: Large single crystals can be formed by precise gradient-temperature scanning, from a higher hold temperature (approx. 37°C) to a low temperature stage (33–35°C). The size and color of the crystal are dependent on the cooling conditions—in this example, a liquid crystal is cooled from a blue phase (BPII) to form green crystals in its BPI phase. Image composed of Figures 2 and 3 from [2], used under a Creative Commons Attribution (CC BY 4.0) license.
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