In astrophotography, the field of view refers to the extent of the sky that is visible in the captured image. It is determined by several factors such as the focal length of the telescope, the size of the camera sensor, and the pixel size of the sensor.

The field of view is usually expressed in degrees, arcminutes or arcseconds. A wider field of view allows capturing a larger portion of the sky, which is useful for imaging large objects such as galaxies or nebulae. On the other hand, a narrower field of view can be used for imaging smaller objects such as planets and smaller planetary nebulae, with greater magnification and detail.

It is affected by several parameters, including:

1. Focal length: This is the distance between the lens and the focal point. The longer the focal length, the smaller the field of view.

2. Sensor size: The size of the camera sensor also affects the field of view. A larger sensor will capture more of the sky, resulting in a wider field of view.

3. Pixel size: The size of the pixels on the camera sensor also plays a role in determining the field of view. Smaller pixels allow for more detail, but can result in a narrower field of view.

4. Telescope or lens aperture: The size of the aperture determines how much light can be captured and affects the depth of field. Larger apertures allow for more light, but can also result in a narrower field of view.

5. Barlow lens or reducer: The use of a Barlow lens or reducer can affect the field of view by magnifying or decreasing the size of the image.

6. Mount type and tracking accuracy: The mount type and tracking accuracy affect the ability to capture a wide field of view over a longer exposure time. A stable mount with accurate tracking will allow for longer exposures and wider fields of view.