While astrophotography is by no means a new discipline, it’s certainly increasing in popularity. Over the last couple of years we’ve seen a huge spike in quality images of the night sky, especially focusing on the Milky Way. More and more photographers are shooting into the wee hours of the night to capture unique images of some of the world’s most iconic (and often photographed) spots.
The following is a quick guide to get you started shooting the night sky, and we’ll focus on techniques to ensure your stars are as sharp as possible. As with all photography, different styles exist, and this is especially true in the world of astrophotography. There is no “right” or “wrong.” Some prefer having an extremely dark sky with a silhouetted foreground while others like images that almost appear to be shot mid-day. It’s entirely up to you!
What You Need
Naturally you will need a dark sky. It’s the best to get far away from cities and light pollution, but sometimes that’s just not possible. A little bit of light pollution can even add some neat color to your night sky. Of course no moon will result in the brightest stars, but even having a half moon can be ideal for lighting your foreground.
A sturdy tripod. Any slow shutter-speed shot requires the use of a sturdy tripod and astrophotography is no exception, as typical shutter speeds range from 15-30 seconds.
A camera that shoots in Manual (M) Mode and ideally one that has solid low-light performance.
A fast, wide angle lens. A minimum aperture of 2.8 or lower is recommended.
A cable release or intervalometer. It’s always best practice to use a cable release to prevent vibration, but depending on your camera (full frame [35mm] vs. crop sensor) and focal length you may want to fire exposures longer than 30 seconds, requiring bulb-mode and a remote timer or intervalometer.
The Other Pieces of the Puzzle
Aperture. Since shutter speeds will not be very long we strongly recommend opening your aperature as wide as possible. We shoot at f1.2 to f4.
ISO. This is a huge factor in explaining why some cameras just plain out-perform others in astrophotography. ISO’s for the night sky typically range from around 1,000 to 6,400. Start with the longest possible shutter speed you can have in order to keep your stars sharp and then adjust your ISO accordingly, with the aperature wide open.
White Balance. Since you’ll be shooting in RAW you can always adjust your white balance in post, but it’s still best to use your Kelvin scale while shooting the night sky.
Focus. Focusing at the night sky can be a bit tricky as you won’t be able to rely on autofocus. For most instances simply setting your focus at infinity will do the job. However, more advanced shooters may opt for focusing user hyperfocal distance. This is certainly a preference call.
There is a small amount of math involved in order to obtain tack sharp stars. Unless you’re purposely shooting for star trails, slight movement in stars just leaves you with a “soft” night sky. What’s the longest shutter speed you can use before those round points become ovals or lines?
We use a rather simple formula that many refer to as the “500 Rule.” The basic formula divides 500 by your 35mm equivalent focal length. At 24mm you will come up with a shutter speed of roughly 21 seconds. That means at 24mm on a full frame sensor (or 16mm on APS-C) one can capture tack sharp stars at up to a 21 second shutter speed (we usually round down to 20 seconds).
Divide 500 by your 35mm equivalent focal length.
500 ÷ [focal length] = Max allowable Shutter Speed (in seconds) for sharp stars (round down).
This should now explain why we recommend the fastest, wide angle lenses to obtain tack sharp stars as the wider the lens you have, the longer your exposure can be, thus keeping your ISO lower. The shorter the exposure time, the higher the ISO must be.
These are the basics for getting the Milk Way and constellations tack sharp. Calculate the appropriate shutter speed for your focal length using the “500 rule” as a guide, set aperture as large as possible (f1.2-f4) and adjust your ISO. The rest is up to you! Get creative. Panoramas, light painting, focus stacking and exposure blending techniques can all be utilized to enhance your sharp night sky.
*For even more detail, including recommended gear, phone apps and a user-friendly “500 Rule” chart check out RRS customer, Dave Morrow’s Star Photography Tutorial