Get ready! This past week, I finished up my first article for Outside Magazine. The article is aimed at helping you get started with taking photos of the Milky Way and the night sky. I cover everything from gear to finding the right spots, picking the perfect nights, and even an intro to camera settings. It’s basically a mini crash for nightscape photography, so you can get out there and start chasing stars right away.

I’m super stoked to be working with Outside! We have a few more articles in the works that will be coming out over the next few months, too. So keep an eye out for them here and in my Instagram stories

You can check out the article on the Outside Magazine website here. Give it a read and let me know what you think!

The NPF rule provides a quick method for determining the maximum shutter speed that can be used in your shot without causing star trails when shooting astrophotography and nightscape photography. If you’re familiar with the 500 rule (or 600, or 400 rule), it’s kind of similar but provides more accurate results, especially with today’s higher megapixel cameras. If you’re not familiar with the 500 rule, then don’t worry! We’re going to cover that too.

A key challenge in night sky photography is achieving correct exposure in conditions with little to no light. The exposure triangle—shutter speed, aperture, and ISO—becomes a delicate balancing act when shooting at night. We can increase the ISO, which can help, but it also introduces more noise the higher we go. The apertures of our lens are limited in how wide they can open. But shooting them wide open also increases coma and can distort the stars. This leaves us with shutter speed. Our first instinct might be to go with the slowest possible shutter to allow the most light to reach the sensor. But since this beautiful rock that we call Earth is flying through space and rotating, if we use a shutter speed that’s too slow, we’ll start to notice motion blur in the stars, or as we in the biz call it, star trails.  Star trails are great if that’s what you’re going for. But if you’re looking for a nice, pretty shot of a sky full of stars, using a shutter speed that’s too slow will turn those beautiful points of light into streaks or ovals instead of sharp dots. But don’t worry, there’s an easy way to figure this out! In this week’s quick tip, we’re going to look at how to calculate your maximum shutter speed for nightscape photography and how the NPF Rule helps you capture sharp, pinpoint stars. 

The NPF Rule

Now, before we dive into the NPF Rule, let me preface it by saying this might sound a bit complicated at first. But stick with me to the end because I have a very simple way to handle it. A few years ago, French photographer and amateur astronomer Frédéric Michaud sought a better solution that worked with the vast array of modern cameras and sensors available today. After lots of hard work, he developed what is now known as the NPF rule. The three letters in its name are actually the variables in his equation instead of an abbreviation. They stand for:

N = Aperture (the letter N is used to represent aperture in the optics world)

P = Pixel pitch (essentially the density of pixels on the sensor)

F = Focal length (from the lens you are using)

Frédéric’s formula considers much more than the old 500 rule, including the camera’s sensor size, the lens aperture, and how densely the pixels are packed on your sensor. However, it is more complex and not something you’d want to be scribbling out by hand in the dark like a mad scientist in the night. Luckily, apps like PhotoPills provide quick calculators where you just select your camera, focal length, and aperture, then the app does the rest. In PhotoPills, you can find it inside the Spot Stars pill. As a bonus, PhotoPills can also account for star declination. More on this in a future article, but it essentially indicates how far north or south a star is from the celestial equator, helping us estimate how fast it seems to move through the sky and form trails.

NowwNow, depending on what your output is going to be for that shot (social media post, digital, small prints, large print, etc), you may want to bend the rules a little bit. For example, if I know the shot is only going to be used for digital outputs like a post on instagram or a timelapse, then I might increase my shutter from 11 seconds up to 12 or 13. If I think I might print the photo in the future, I’ll stay as close as possible to the NPR Rule’s shutter speed. You’ll want to experiment a bit to see how much you can bend the rule and still achieve results youare okay with. And again, doing math while out on a beautiful night under the stars is probably not something you want to deal with while setting up your shot, so I’d highly recommend downloading PhotoPills. The NPF rule calculator is just one of the many reasons I love that app so much. It’s my go-to for planning shots, scouting locations, and a wide range of other tasks. 

Interested in capturing stunning nightscapes and night sky photos? Join my one-on-one online classes, personalized tutoring sessions, or immersive in-person photography workshops, and let me help you unlock your full potential. Whether you’re just starting out or looking to elevate your skills to new heights, I can guide you to create breathtaking images. Check out this link for more info!