Night Sky April 27, 2026 3 min read

Night Sky Photography: How Far Away Are the Stars?

The nearest star beyond the Sun is Proxima Centauri, about 4.24 light years away, or roughly 40 trillion kilometres. The stars of the Milky Way's core are around 25,000 light years off. For a photographer, this has one consequence: stars are at infinity, and no aperture or lens changes that.

How far away things are

Object	Distance	For focusing
Moon	384,400 km	Infinity
Sun	150 million km	Infinity
Proxima Centauri	4.24 light years	Infinity (telescope only)
Sirius	8.6 light years	Infinity
Milky Way core	25,000 to 27,000 light years	Infinity
Andromeda Galaxy	2.5 million light years	Infinity

Never point a camera at the Sun without a proper solar filter, since it can damage the sensor, and the eye if you use a viewfinder.

What infinity means for focus

At infinity, the light from a point arrives as parallel rays, which the lens brings to a point on the sensor when focused there. But infinity focus has a catch that is often missed: it is not the same as everything being sharp. When you focus at infinity, only objects beyond the hyperfocal distance are sharp, so a foreground nearer than that is soft. For a 24 mm lens at f/2.8 on full frame, the hyperfocal distance is about 7 m, and for a 14 mm lens at f/2.8 about 2.4 m. The table on the astrophotography depth of field post lists more lenses and apertures.

If you focus at the hyperfocal distance instead to bring the foreground in, stars sit at the edge of the sharp zone, and they swell to discs about 5 pixels wide on a 24 MP sensor. For serious work, shoot the sky and the foreground as separate exposures and blend them.

Finding true infinity

The infinity mark on many lenses is unreliable, because lenses are built with some focus travel beyond true infinity. Use manual focus and live view, magnified, on a bright star or planet, and adjust until the point is as small as possible. Doing it at twilight on a distant light or a bright planet is easier than in full darkness. Once set, tape the ring. Another way is to focus in daylight on something more than a kilometre away, then switch to manual to hold it, though you should still check on a star.

The Moon is the exception

The Moon is the one night-sky object where the subject distance calculator really applies, since its size (3,474 km) and distance (384,400 km on average) are known. A full Moon covers about 0.52 degrees. A 500 mm lens puts it at about 4.5 mm on the sensor, which is 19 percent of the height of a full-frame image. A 1000 mm lens gives about 9 mm, or 38 percent. That is why lunar photographers use very long lenses.

The Moon's distance varies, from about 356,500 km at perigee to 406,700 km at apogee. At perigee it appears about 14 percent larger across, so the same lens fills 14 percent more of the frame. You can check this by entering the Moon's diameter and each distance in the calculator and comparing the image heights.

Star trails and exposure length

The sky turns by 15 arcseconds per second, so stars trail in a long exposure. The 500 rule, 500 divided by the focal length, is a quick estimate, but on a 24 MP full-frame sensor it still allows trails of about 6 pixels at 24 mm, and 8 pixels on 45 MP. A more conservative option is the NPF rule, which accounts for aperture and pixel size and gives about 12 seconds on 24 MP at 24 mm and f/2.8. The astrophotography post has the formula. A tracking mount removes the problem completely by turning the camera with the sky.