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Forbear vs. Awesomely vs. Fat vs. Sonhood vs. Ricochet vs. Channel vs. Trending Comparisons. The iris of a lens is a means to the aperture, which ultimately is what affects the final image captured by a camera. A comparison between an iris and pupil and an iris and aperture can be seen in Figure 1. The smaller the aperture, the more focused the light will be, allowing for a larger depth of field DOF — covered in more detail later.
This is inversely proportional to the amount of light that reaches the sensor. So, when trying to achieve a bright and focused image, aperture plays an important role. However, sometimes its relationship with focus and brightness might not be desirable. This blog covers the different ways to adjust aperture, how to take advantage of its optical impact, and provides alternative options for getting bright and focused images in various conditions.
The aperture of a lens is the opening through which light passes to reach the camera. Adjusting the aperture means making that opening larger or smaller with a lens diaphragm usually made up of metal blades or leafs within the lens.
The number of blades within the diaphragm can vary significantly, as shown by the comparison of various lens diaphragms in Figure 2. A lens with the diaphragm wide open is referred to as having a large aperture. The somewhat less intuitive aspect of aperture is that the more open the iris, the smaller the number used to represent its size.
In this context, it becomes clear that the lower numerical value of an f-stop represents a bigger portion of the lens diaphragm opening up for more light to enter. This produces a well-illuminated image.
However, if the aperture is too open this can cause a significant reduction in the DOF. This is often referred to as a narrow DOF. The DOF is the distance between the nearest and furthest target within the image that remain in focus, represented by the diagram in Figure 4.
The DOF and the amount of light passing through the lens are inversely proportional. So, it can be challenging to get enough of an image in focus, such as Figure 5, while also having enough light to illuminate the target clearly.
However, the reduction in light reaching the sensor does not mean that a camera cannot take advantage of a larger DOF. The smaller aperture allows more of the image to remain in focus, providing useful information on the targets further away. Additionally, by using a camera that can capture RAW images, such as the Teledyne Lumenera LtR, images can be processed to reveal far more image data then would be shown by default.
An example of this is shown in Figure 7 where a seemingly dark target can be revealed by manipulating the image data. To adjust for having a greater DOF and having most of the image in focus, the camera may need to increase the gain value.
By increasing the gain the increased sensitivity will not only result in a brighter image, but it will also include more noise, as shown in Figure 8. Relying on gain too heavily to brighten an image can result in poor quality instead of allowing more light to enter the lens with a wider aperture.
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