![]() The longer the focal length, the more the stars are magnified, the faster the camera's movement causes them to cross over pixel wells (the source of motion blur), and the shorter the tolerable exposure durations become.įor example, 14mm is half of 28mm, and the 2x longer exposure available at 14mm equates to a full stop of aperture or noise within the tolerable exposure duration.Īlso factoring into the exposure consideration is the pixel density of the imaging sensor. The amount of action in the night sky is also dependent on the focal length selected. Since wide-angle focal lengths take in a wide area of the sky, the stars appearing to move the fastest generally need to be accounted for. The amount of action in the night sky is dependent on the distance of the subject stars from the north star, which doesn't move. While the stars appear to be motionless, the required exposures are so long that the earth's rotation promotes night sky photography into a form of action photography. If it is dark, simply use a longer exposure, right? When stars and the Milky Way are visible, the night sky is extremely dark, and that darkness sets the stage for the next night sky lens selection criteria. Primarily, we are referring to light pollution filters as blocking any other light is detrimental to night sky photography. Some of the widest-angle lenses have bulbous front elements that preclude front filter use. Related to focal length is the availability of front filter threads. Keeping a foreground and the stars sharp (without focus bracketing) is easier with a wider-angle focal length. I'll talk more about this issue in the next section.Īnother factor is that longer focal lengths provide shallower depth of field. Other aspects must be factored into the focal length choice.įor example, the longer the focal length, the shorter the exposure required not to exceed the minimum acceptable star trails. ![]() However, 14mm, 20mm, and 24mm lenses are usually in my Milky Way pack, and long exposures provide time to operate two camera setups simultaneously. ![]() What is my favorite Milky Way lens focal length from an angle of view consideration? However, a longer focal length expands the width of the Milky Way in the frame, resulting in a higher percentage of the frame filled with Milky Way. We see that the longer the focal length, the less Milky Way length fits in the frame. Here is an illustration showing what the full-frame 14-35mm focal length range looks like with the Milky Way in the frame: The title image for this page is a 12mm capture. The widest focal lengths available are great for this pursuit. While nearly any wide angle of view can be used for nightscapes, I seldom use a focal length longer than 24mm and rarely go longer than 35mm (full-frame angle of view reference). Selecting the optimal focal length is usually the first step in choosing a lens for any purpose, and it is for this one. Let's take a closer look at these requirements. That is not an easy set of requirements to fill.
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