Spending hours in the dark last week photographing the Milky Way, I was reminded of a few questions I was recently asked about focusing at night. We teach a number of workshops that photograph stars and the northern lights. With the amazing ability of modern digital cameras to capture night skies, all photographers should be giving this a try…shooting in the dark is a blast!
But focusing at night is not a blast. But there are few tips that will solve this challenge, and you don’t have to perform them in the dark. First, with DSLRs, figuring out focus is pretty simple. Since the stars are at infinity, I put on my trusty 14-24mm F2.8 and focus on a distant subject that is at infinity. Any distant mountain, hilltop or water tower will do. I use autofocus to do this, and once I have focused, I check to see where the focus infinity mark is on my lens focus guide. Here is the interesting part. Even though you might be focused on infinity, the lens infinity mark may not line up perfectly at the focus point. Take a look at the image above. The infinity mark (the figure ‘8’ symbol) is off to the side of the focus point, but I know this is perfectly focused for infinity with this lens. I’ve had four of the same lenses on a workshop, and they all focused to different spots for infinity. But once you know what the infinity focus point is, you are ready to go. I know exactly where it is on my 14-24mm, so if I am shooting at night I just manually set this focus distance on the lens and I know I will have razor sharp stars. When we photograph northern lights in Alaska, we gaffer tape the lens to this point…one less thing to worry about at 20 below zero.
But what about mirrorless lenses? Mirrorless lenses focus by wire, meaning the focus is set electronically, not physically like turning the focus ring on a DSLR lens and the glass elements actually move. When you turn off your mirrorless camera, you lose your focus point…so much for gaffer taping a lens to a set focus point. If you have a high end mirrorless lens, it might have a focus scale on it. Take a look at the image above of Nikon’s two 24-70mm lenses. The smaller 24-70mm F4 does not have any focus guide on the outside of the lens, while the much more expensive 24-70mm F2.8 does. Here is the good news if you have a scale on the outside. Just turn on your mirrorless camera, and manually adjust the focus until it is set to infinity (should have the same ‘8’ symbol). Since mirrorless cameras focus right off the sensor, setting focus at the infinity mark should work.
If your lens doesn’t have a focus guide on the outside, you will have to use the viewfinder or live view to help. With a Nikon Z6/7, just set the lens to manual focus, and start to turn the focus ring on the lens (make sure it is set to ‘focus’ and not another feature like exposure comp). You will see both a focus peaking guide and a scale showing you focus distance. Turn the focus ring until the focus scale reaches infinity. Focus peaking will show in red what is in focus, which helps with focusing at night. But I look at the focus scale on the back of the camera to know when I am at infinity focus.
Nikon has a fantastic 14-30mm F4 super wide angle lens for the Z mirrorless system. Small, compact and sharp, it is perfect for landscape and travel. For star trails the F4 minimum aperture makes it not quite as nice as a faster lens like a F2.8 or F1.8. Using the 500 rule, 500 divided by 14 gives us 35 seconds. This rule states that exposures 35 seconds or shorter shouldn’t record star movement. I find I am more conservative with this rule, and would like to keep shutter speeds at 30 seconds or shorter to avoid movement. Last week in Capitol Reef my exposure for the image at the top of this post was ISO 3200, 15 seconds at F2. If my minimum aperture was F4, two stops less light, I would have to shoot at ISO 6400 at 30 seconds. You can still get nice images at this ISO with some noise reduction in post, but having a fast lens like F2.8 or faster is really helpful for night shooting. Nikon is soon to announce their 14-24mm F2.8 S lens for the Z system, and I can’t wait.
Another technique I was experimenting with in Capital Reef NP last week was stacking multiple star images versus just shooting one. Stacking images is known to produce a single shot with much less noise than shooting a single frame. But is there that big of difference? Stacking images takes some time, and more time in post. Stay tuned…this is one topic we will be covering in our upcoming online Advanced Landscape photography class.