Shooting the Milky Way with an 85mm Lens Sans Star Trails

When shooting the night sky, I am usually using a wide angle lens. However, a telephoto lens renders stars larger and provides a different look to a night sky photo.
 
To avoid star trails, a telephoto focal length requires a shorter exposure than a wide angle lens. A simple rule of thumb to use for determining the longest exposure time that can be used without star trails becoming problematic is 600/(focal length). By this formula, a 14mm lens requires a 43 second or shorter exposure. An 18mm lens requires 33 seconds or less and 24mm can use no more than 25 seconds.
 
I tend to like an at-least 1/3-stop shorter exposure than this rule calculates. If you are happy with relatively-sharp stars at 14mm at 30 seconds and at 24mm at 20 seconds, you probably do not want to exceed roughly 5 seconds at 85mm.
 
Obtaining an adequately bright image at these exposure limitations generally means using the widest aperture the lens has with an f/2.8 or wider lens being my preference. A lens that opens to f/1.4 as this one does is ideal for night sky photography. Even with ultra-wide apertures, a high ISO will still be required. In this case, ISO 5000.
 
Note that, unless you need shot-to-shot times to be short, enabling long exposure noise reduction will make a nice difference in the noise levels of your results when shooting the night sky.


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