Astrophotography settings tips and formulas guide

Astrophotography is unique. It’s the art of beholding the beauty of the stars beyond our reach. However, the key word here is “beauty” and not “blurry,” meaning your astrophotography settings are essential for capturing illuminating images of the Milky Way. Producing a mediocre shot after spending hours trying to capture the perfect night sky essence is no fun. So, today’s post will cover some critical, easy-to-remember tips regarding good camera settings for astrophotography.

Astrophotography doesn’t have to be complicated, but working in lowlight situations with long exposures can lead to undesirable results. That’s why it’s crucial to have a good grasp on appropriate camera settings for astrophotography. Some variables will change depending on your camera, but here’s everything we’ll cover to ensure you’re prepared to shoot the Milky Way the right way.

Star photography guide
Photo by Rishav Banerji

Table Of Contents

First, let’s cover the vital three pillars of exposure (also known as the exposure triangle), especially when it comes to long- exposure. This will include aperture, ISO, and shutter speed. You’ll need to manually adjust all these to get well-exposed and clear-cut images.

Aperture

Aperture refers to how wide or narrow your lens will open, affecting the amount of light being let in. The number is represented in “f/stops”. For example, the NIKKOR Z 28-75mm f/2.8 lens has an aperture of f/2.8. The higher the number, the less light is let in (or, the narrower the lens gets). The lower the number, the more light it lets in (or wider the aperture opens).

Regarding astrophotography settings, you’ll want a wider aperture (or lower f/stop) due to the dark nighttime conditions. This ensures you capture an efficient amount of light to see the image. A good number for this is f/2.8. However, if your lens doesn’t go that low, it’s not the end of the world, but it will be more difficult to see (f/4 is also an ideal aperture).

Camera settings for astrophotography
Photo by Ivan Torres

ISO

ISO (International Standards Organization) affects the sensitivity of your camera to light. But rather than doing this through opening and closing (like the aperture), it controls the sensor sensitivity (try saying that 5x fast). In this case, the number scale works opposite to the aperture; the higher the number, the brighter the image.

Once again, you’ll want to bump this number up because it’ll be dark out. A good starting point is around 1600 ISO for your camera’s astrophotography settings. Depending on your situation, between that and 800 or even up to 3200 can work. However, it’s important to remember that a high ISO will add “noise” to your photo and can ruin your image. You want to be able to see the night sky, but you also want a clean picture.

Astrophotography star trails
Photo by Samuele Errico

Shutter

The shutter speed refers to how long the camera’s shutter will stay open (like your eyelids when you blink). This is measured in seconds or fractions of a second. In the case of astrophotography settings, you’ll want your shutter open for much longer than usual. Rather than 1/100, 1/60, or 1/30 of a second, we’re talking 15, 20, or 25 seconds long. There are a few ways to approach this. If you want simple and aren’t obsessed with the perfect number, anywhere from 20-30 seconds should be good.

However, there are two other methods that you can use to find a more accurately calculated shutter speed called the – 500 Rule (sometimes also known as the 400/600 rule) and the NPF formula or NPF equation. I will elaborate more on these photography formulas further down in the post.

Lens & Focal Length

To capture the sharpest image of the Milky Way possible, you’ll want to go for a short focal length of ideally around 16mm -24mm. A wide or ultra-wide lens will allow you to capture a large chunk of the landscape and stars for an authentic nighttime shot. These lenses will help give you a greater depth of field, keeping your foreground and background of the landscape in focus.

That said, if you don’t have a wide-angle lens, you can still use a longer focal length. Sometimes this can be used to purposefully create star trails adding motion and creativity to your picture.  The wider the lens, the more information in your image, so be aware of shot composition. If you go lower than this focal length, you’ll also need to be mindful that distortion can start to take place.

Star photography settings
Photo by Mindaugas Vitkus

Auto-Focus – Turn Off

For astrophotography, you’ll want to turn off AF. Due to the lack of light, your camera will struggle to find a point of focus. To avoid this, you will want to manually focus on the brightest star, the moon, or the next distant object in view (like mountain tops or trees).

White Balance

White balance will adjust for the color temperature displayed in the camera image. There are warm colors like orange, yellow, and red or cool colors like purple or blue. To keep things short and simple, you’ll want to shoot in Auto-White Balance (AWB) in most scenarios. However, you may want to adjust due to other factors such as light pollution, in which case 3,200K or a neutral white is an excellent place to start.

White balance color temperature guide for star photography
Color Temperature Guide Courtesy of Exposure Guide

File Format

You will want to shoot in RAW for the best results in terms of file format. This will ensure you capture as much color detail as possible, in addition to reducing image compression and noise. You’ll also have more post-production capabilities with adjusting aspects like dynamic range.

Extra Tips & Important Gear

  • Long exposure noise reduction – Turn off (if applicable)
  • Flash – Turn off
  • Tripod – long exposure makes it easy to ruin your shot with the slightest movement. Using a tripod will play a crucial role in securely locking your camera in place.
  • Remote shutter release – once again, you don’t want to have to touch the camera when taking your shot. Using this or a timer for your shutter will be crucial.
Astrophotography tips and settings
Photo by Jeremy Thomas

Helpful Photography Formulas to Know

What Is the 500 Rule Of Photography?

The 500 rule (also known as the 400 rule or 600 rule) is an excellent template for photographers who are new to astrophotography or can’t figure out what shutter speed to put. It is designed to help you find a reasonable shutter speed range for your best shots.

However, it should be noted that this equation isn’t an end-all to astrophotography shutter speeds because it doesn’t account for all factors while shooting.

Alright, ready for some fun math class nostalgia?

To use the 500 rule, you simply take 500 and divide it by the focal length of your camera. For example, if your focal length is 24mm, you would do: 500 ÷ 24 = 20.83. This means you would set your shutter speed to about 20 seconds. Nice and easy.

500 ÷ (Focal Length) = Shutter Speed 

Photo of the stars and night sky
Photo by Jacob Dyer

What is the NPF Rule/Formula?

For those of you who’re looking for more of a mathematical challenge, you can use the NPF formula for even sharper images. The NPF formula is another equation created by Frédéric Michaud to find a more accurate shutter speed for your night shots. The only exception is that the formula is much more complicated because it factors in more elements such as pixel density, width, aperture, and focal length (shown below).

The equation requires you to know: F-stop or aperture, focal length (mm), pixel pitch (micrometers/μm).

  • N = Aperture.
  • P = Pixel density (pixel pitch), the distance between the pixels on the camera sensor.
  • F = Focal length.

First, you need to find the pixel pitch, which is the distance from the center of one pixel to the next nearest pixel. To find this, you need to divide the width of your camera’s sensor (mm) by the total number of pixels within that width. After, multiply that number by 1,000 to get your answer in micrometers/microns (μm).

Here’s an example for the Canon EOS R6: the senor is 36mm x 24mm, and the pixel dimensions are 5472 x 3648. So the equation would be:

36 ÷ 5472 x 1,000= 6.57 μm

Photo of the stars, photography tips
Photo by Andrew Gloor

Now, all you do is add your pixel pitch to the complete equation. To make things easier, we’ve used a simplified version of the equation, which uses averages for factors like declination and latitude (shown below):

(35 x aperture + 30 x pixel pitch) ÷ focal length = shutter speed in seconds

Using the Canon EOS R6Canon RF 15-35mm f/2.8L IS USM Lens:

(35 x 2.8 + 30 x 6.5) ÷ 15 = 19 seconds

Now, for anyone whose head hurts as much as mine from looking at too many numbers for too long, you can also just use an NPF calculator site. It helps to download these apps on your phone or computer when you’re out shooting and need quick assistance.

Conclusion

Your camera settings for astrophotography do matter, but not everything has to be perfect. After all, it is your work, and you have complete control of what you choose to do with it. Finding the settings you’re most fond of will take time, and as long as you’ve established the basics, the rest will come over time. Finally, have fun.

Tell us how your astrophotography is going. Have you discovered any neat tips and tricks along the way?

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