If you are new to astrophotography, you might come across some unfamiliar terms and concepts that can be confusing. When I first got into this hobby, I found myself constantly searching on Google. Unfortunately, this only added to my frustration because there were so many search results to sift through, most of which were written in language that was too technical for beginners. If you are just starting astrophotography these definitions will help you understand the basic terminology used in astrophotography and astronomy.
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Aperture
Aperture refers to the amount of light that can pass through an optical or photographic instrument. Think of it like a pupil. When it is dark, your pupil expands, allowing more light to hit the retina. On a bright sunny day, your pupil shrinks to reduce the light entering your eyes.
Aperture of a camera lens
Pictures of nightscapes or the Milky Way are often captured using a camera and lens. In this scenario, the aperture refers to the opening in the lens that lets light into the camera. In most lenses, this is adjustable. The aperture of a lens is measured in f-stops. A higher f-number indicates a smaller aperture opening. For example, an aperture of f/1.4 allows a lot of light to pass through, while an aperture of f/32 allows very little light.
The aperture setting has a significant impact on your photographs in two main ways:
Exposure: The size of the aperture determines the amount of light that reaches the camera sensor, affecting the brightness of your image.
Depth of Field: The aperture can add dimension to your photos by controlling the depth of field. A wide aperture (small f-number) gives a shallow focus effect with a blurred background, which is popular for portrait photography. A small aperture (large f-number) gives sharp photos from the nearby foreground to the distant horizon, often used in landscape photography.
Aperture of a telescope
In a telescope, the aperture is determined by the size of the main light-collecting part. In a refracting telescope, this is the objective lens, and in a reflecting telescope, it’s the primary mirror. Just like a bigger bucket can collect more rain, a larger aperture can collect more starlight, making the image you see through the telescope brighter and clearer.
The aperture of a telescope is expressed in millimetres based on the size of the primary mirror or objective lens. For example, Skywatchers 150 (aperture in millimetres) | 750 (focal length in millimetres) Black Diamond Newtonian (reflecting telescope). The 'f-stop' number can be calculated by dividing the focal length by the diameter of the main light-collecting part. For example, a telescope with a focal length of 750 millimetres and a primary mirror that is 150 millimetres in diameter, has an f-stop number of F4. Learn more about refracting and reflecting telescopes.
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