Photographing the Stars 3

Milky Way with Nikon Z6 and 24mm lens

In this post, I am carrying on from the previous post and cover the final steps needed to take your first constellation photos. The exposure table in the last post gives you a guide of what to do to avoid star trails. If you want star trails, then just take a longer exposure. Just be a ware that longer exposures may have problems with light pollution. You can mitigate that by reducing the aperture slightly to say f/4 or f/5.6 and reducing the ISO.

Taking the Exposure

There are a few other factors about taking our photos that we need to give some thought to. At the moment, we are just using a camera with a conventional lens. To take our pictures, we are going to be boosting the ISO and taking a long exposure of perhaps as much as 25 seconds. We’re going to have to take some extra precautions.

Our enemy here is camera shake and vibration. If we don’t do something to protect against these, our images will be blurred and the stars won’t be round, but will be elongated.

The simplest way to support our camera is to mount it on a tripod. For the kind of images we’re taking, being level isn’t too big an issue. The legs should be spread out to maximise stability. Avoid raising the central column as that will add leverage and increase the risk of vibration. Make sure everything is tightened up, including the bolt attaching the camera to the tripod’s quick release plate. If your lens has a mounting collar, then use that to attach to the tripod as it will provide a better balance. 

You can improve the stability of some tripods by hanging a weight from the bottom of the central pillar. Some tripods have a hook to do this. This is why very light tripods should be avoided for astrophotography. 

Your other cause of vibration is when you open and close the shutter. The act of touching the camera to open the shutter will introduce vibrations. Even if these vibrations damp out in less than a second, it’s enough to spoil your images.

There are several ways of avoiding this. Some cameras have an option to delay shutter release, which can usually be set to a range of values between about 0.1 to 5 seconds. A value of 2 seconds is probably enough. When you press the shutter release, nothing happens for two seconds, allowing time for vibrations to fade away.

You can attach some sort of remote release to your camera. There are numerous options here, depending on your camera. There is probably a bespoke remote release cable that can be attached to your camera. Some cameras have an infrared remote control, which has no wires, and it will trigger the shutter. Depending on your camera, you may be able to attach a wireless trigger. This usually attaches to the hot shoe, but it may require a cable from the receiving unit to the remote socket on the camera to actually work. There will be a separate trigger unit which you use to fire the camera.

There may be a phone app for controlling your camera, either through wi-fi or via Bluetooth. 

All of the above methods are ways of remotely triggering your shutter. Just be aware that if you are using the bulb (B) setting, you fire once to open the shutter and again to close it. If you’ve set the exposure to say 20s, which is a valid value for your camera, you only need to trigger it the once. 

If you use a DSLR, which has a mirror, you may wish to consider locking the mirror up since mirror bounce is a major source of vibration. This is not an issue for users of mirrorless cameras. Be aware that you need enough battery charge to use mirror lock. 

Just be aware that some remote operations, particularly Bluetooth, can be heavy users of the camera’s battery. This is worse in cold weather which adversely impacts battery performance. 

For completeness, I’m going to mention the ‘top hat’ method. If you do not have a remote release, you can do what used to be done before they existed. You need something to cover the lens, but it mustn’t be touching the camera or lens, so a top hat is ideal… but anything that covers the lens will work.

You place your ‘hat’ over the lens, trigger the exposure, then a second or so later you uncover the lens by removing the hat, being careful not to hit the camera. At the end of the exposure, you cover the lens with the hat and then release the shutter if on B – it will do it itself if it’s using a valid exposure time. The top hat is ideal since it is deep which prevents stray light entering. Of course, you don’t need a top hat, but whatever you use needs to have similar properties.

You should now have a constellation photo, or star trails if you took a longer exposure. I will talk more in later posts about what you can do to process your images. 

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