Choosing a coupler that is suitable to connect a camera to a microscope is a critical step in the configuration of the instrument. A coupler is also known as a C-mount adapter, and these two terms are often used interchangeably.
To optimize the field of view of a camera without compromising its image quality, various factors have to be taken into consideration while choosing a coupler.
This article discusses tips and general guidelines for coupler selection, covering the basics that are essential to produce an evenly illuminated image.
Maximizing A Camera’s Field of View
There are three major factors that determine a camera’s field of view. These include the camera’s sensor format, the magnification of the coupler, and the field number (FN) of the microscope.
The FN depends on the microscope and usually varies between 20 and 26 mm. A camera’s sensor format refers to the size of the image sensor. The most commonly used sensor formats for microscopy cameras include 1/3", 1/2", 2/3", and 1".
The reference provided in Table 1 must be followed as a rule of thumb to obtain even illumination across the camera’s entire field of view. The reference assumes a relatively low FN to enable compatibility with a broad range of microscopes.
Table 1. Reference Points
If the magnification of the chosen coupler is too small, a phenomenon known as vignetting will occur. This phenomenon also occurs when there is a drop in illumination in the outer regions of an image, starting from the corners.
This is caused as the image sensor of the camera is rectangular in shape and the optics in the microscope creates a circular image. When the circular field of view projected by the magnification of the coupler is smaller than the whole area of the image sensor, then the corners of the image darkens, resulting in a vignetting effect.
Figure 1 shows a variation of coupler magnification with INFINITY3-3URC camera with 2/3" sensor and 40x objective.
Figure 1. Variation of coupler magnification with 40x objective and INFINITY3-3URC camera with 2/3" sensor.
Vignetting can be avoided in most microscopes by following the recommendation mentioned above.
This information has been sourced, reviewed and adapted from materials provided by Lumenera Corporation.
For more information on this source, please visit Lumenera Corporation.