To photograph stars without star trails, start with a wide lens, a tripod, and a short test exposure. The right shutter speed is the longest one that still gives you round stars at the size you plan to share or print.
Set up your camera and focus on a star
Mount your camera on a stable tripod and switch to manual exposure. Shoot RAW if available. Open the aperture to f/2.8 if your lens supports it, or start with its widest usable aperture. Set ISO 1600 as a starting point. On the live view screen, magnify a bright star and turn the focus ring until the star is as small as possible. Check focus again if you change focal length.
Run a three-exposure shutter speed test
With a wide lens such as a 24 mm full-frame equivalent, take three frames at 5, 10, and 15 seconds. Keep the composition, aperture, and ISO fixed. These are illustrative starting points. Your camera, lens, and direction in the sky will affect the results.
Zoom in on the same star near the center of each frame. If the 15-second star looks like a short dash and the 10-second star still looks round, use 10 seconds. If even the 5-second frame looks soft, check focus and tripod stability before changing the exposure again.
Use the 500 rule as a starting estimate
Divide 500 by the full-frame-equivalent focal length. At 24 mm, that gives about 21 seconds. Treat it as an estimate and inspect your test shots. High-resolution photos and tight crops can show movement at shorter exposures. See Nikon’s examples of the 500 rule and star stacking.
What to do if the frame is too dark
Once the stars look round, try a wider aperture if you have room, or raise ISO if the image needs a brighter preview. Raising ISO does not capture more light. For a cleaner sky, shoot several short RAW exposures and align and stack them. When comparing your shots later, record the focal length, shutter speed, aperture, and ISO beside each crop so you can repeat the settings.