Camera Field Of View

Introduction

The area across which your camera can image is known as the field of view or FOV, the larger the FOV the more of your sample you can see. Having a large FOV allows you to take more efficient images containing more data, and take fewer images in order to capture the entire sample. But as with all camera specifications, changes to FOV will affect other vital factors such as resolution and imaging speed.

Similarly to resolution, FOV is dependent on both the microscope and the camera, both of which have upper limits on their max FOV. By pairing a large FOV camera with a large FOV microscope much of your sample can be captured at once, while using a smaller FOV camera with a large FOV microscope will limit the amount of data you can receive even if the microscope can deliver much more.

Camera Field Of View

The camera FOV depends on two factors: the size of the camera sensor and the total magnification. Sensor size can be measured in a number of ways but a commonly used measure is the size of the diagonal across a sensor, as some sensors are square and others rectangular. This is typically displayed in millimeters, and a range of camera sensor sizes can be seen in Figure 1.

CCDs and EMCCDs typically had smaller sensors measuring around 11 mm, this limits what you can image and is well below the maximum of most microscopes.

CMOS cameras offer much larger sensors, typically around 18.8 mm diagonal which matches up well to certain microscope models. Some microscopes can go above 20 mm diagonal, so CMOS cameras are also available with sensor sizes of 22 mm, 25 mm, and even 29 mm.

These larger sensors typically have more pixels, so while an EMCCD would have 0.25 megapixels (MP), CMOS cameras contain anywhere from 1-15 MP depending on the pixel size.

Figure 1: Different camera FOVs displayed on the same sample. While CCD/EMCCDs have small FOVs, CMOS cameras range from 18.8-29 mm in FOV, and can be square or rectangular.

Magnification

A camera with 25 mm diagonal FOV can only image an area this large if the magnification is 1x. With a typical life science magnification of 40x, the camera FOV decreases by a factor of 40, resulting in a 625 µm diagonal FOV.

The greater the magnification, the smaller the FOV, as shown in Figure 2. However, high resolutions depend on high magnifications (see our resolution article for more), and high camera speeds can also be obtained with smaller FOVs. So in order to image at a large FOV, it will affect other factors in your imaging. Luckily, most biological samples are small (from cells to molecules) and often don’t need the entire FOV the camera can offer.

Figure 2: Field of view decreases as magnification increases, limiting the area you can image at higher magnifications.

Matching Camera and Microscope FOV

One thing to keep in mind is that a microscope FOV is circular, and a camera FOV is square/rectangular, as seen in Fig.3 Top. Pairing an 18 mm FOV camera with a 18 mm FOV microscope does result in some areas that are not imaged, but this is largely a common factor with all imaging systems unless circular camera sensors emerge in the future. So for now, the camera FOV should aim to fit within the microscope FOV, meaning that it is best to match the FOV between camera and microscope.

Some rectangular camera sensors can often occupy the microscope FOV more effectively depending on the size, but if the camera FOV is larger than the microscope FOV there will be vignetting, an effect seen at the corners of the image due to the lack of light, as seen in Fig.3 Bot. While this may capture more of the microscope FOV, the substantial image artifacts at the corners of each image can lead to decreased image quality.

Figure 3: Matching camera FOV to microscope FOV. Top) An 18 mm FOV microscope is matched by an 18 mm FOV camera, which fits within the microscope circular FOV. Bot) Having a camera with a larger FOV than the microscope leads to more image capture but introduces vignetting artifacts.

Summary

The field of view of the camera determines how much of your sample you can see. With larger FOVs, cameras can image more effectively and capture a sample in fewer images. However, FOV is decreased at higher magnifications and in order to improve speed, and it should be matched to the model of microscope. By keeping this in mind, you can maximize your FOV and perform more efficient imaging.