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Astrophotography: A Guide

Some of what I have learnt from various Astrophotography attempts

By Blackaptur Photography

Astrophotography is actually far simpler than people might imagine with a relatively low barrier to entry for people to try out, providing they already have a basic understanding of how to use a camera - I will do a glossary of technical terms at the base of this article.

There are a few simple rules and gear recommendations to follow that will make your life easier (based of what I have found) although there are many ways to tackle this and achieve the same or better results - this is just what I have found works well.

Keep in mind throughout the next few tips that the basic principle of taking an effective milky way photo is to let as much light in to your camera as possible while still having sharp, in focus stars.

Location, Timing and Weather

Obviously you need a clear sky, however there are a few key things that all play a part in getting the best possible photos.

In the Southern Hemisphere, the Galactic Centre of the Milky Way is visible from February to October but the true heart of winter is when it is the easiest and best to get crispy clear shots on the cold and long winter nights - June and July is when I find I have the greatest success, but as the Milky Way starts going horizontal across the sky in September and October some interesting compositions can be had.

Apart from clouds in the sky which is the obvious one, the next greatest impact is the moon. You need to pay careful attention to the moon phases and the moonrise times - if it is a full moon the sky will be to bright. The best nights are the one where the moon is almost gone, the beginning of a new moon, or better still isn't there at all. Some nights the moon is either setting or yet to rise and brilliantly dark skies can be had.

The final hurdle is light pollution and picking a location that doesn't have to much but also retaining an interesting foreground of sorts. It's pretty easy to check out whats polluted badly and wants not using a Light Pollution Map - thats the one I use (see below) Although some areas are shown as in the red I have managed to take some milky way photos there but the difference is definitely noticeable - I have detailed some locations close to home I have shot in below - although the dark skies around Tekapo area certainly make your life easier.

Gear Recommendations

A must have list:

Mirrorless or DSLR Camera
Shoot in RAW image files NOT JPEG
Wide angle lens
Adobe Lightroom or Photoshop
Tripod

Most semi-modern DSLR cameras are capable of Astrophotography but you will yield far better results if you can use a Full Frame camera rather than a APS-C/Crop Sensor camera - this lets a lot more light in and these are far more capable of operating at higher ISOs. This applies to Mirrorless cameras also, most newer Mirrorless cameras are exceptionally good at Astrophotography. You must shoot in RAW images to render any decent results. JPEG images will not cut it.

I currently use a Nikon Z6ii Full Frame Mirrorless camera but some of the images in this article are from a Nikon D750 and a Nikon D610 - both Full Frame DSLRs.

The wider your lens is, the longer your shutter can be open - therefore letting in more light. Because stars move 0.25 of a degree every minute, you are limited in how long your exposure time can be before you start creating star trails. To calculate how long you can have your shutter open for, you use a simple formula called the '500 Rule'

500 Divided by Focal length = Shutter Speed - For Example with a 17mm Lens:
500/17 = 29.41 - 29 Seconds
However the longer the focal length, the less time there is before you start getting star trails, this is why having the widest lens you can will produce far brighter and higher quality images:
500/24 = 20 seconds
500/35 = 14 seconds
500/50 = 10 seconds

You can combat this by having a faster aperture lens - like a 24mm f/1.4 will let in 2 stops more light than a 24mm f/2.8 - there are lenses on the market that are 14mm f/1.4 which theoretically would be the best possible lens for wide angle Astrophotography, however these get very expensive.

Tip: If you can use a lens that is 24mm or wider with a aperture of f/2.8 or faster you will be fine.

I use a Nikon 17-35 f/2.8 lens for the majority of photos but have also used my Nikon 24-70 f/2.8 successfully - as you master the art of Astrophotography you can start playing around with longer focal lengths - like these images here I took on an 85mm f/1.4 lens - not usually used for Astro, and only just being possible with the f/1.4 and a lot of stacking (more on that later)

Camera Settings

Please bear in mind that what settings you use does depend entirely on the conditions in which you take the photo, however, these settings may provide a good baseline.

Your camera will obviously need to be in full manual mode.

Shutter Speed: This is directly in relation to focal length, for the purposes of the exercise I will use my 17mm lens - so 29 is the max. length but my camera won't do 29 as a preset number (you could use bulb mode and manually time it) so I use 25, in theory this should give me fractionally sharper stars.

Aperture: As fast/wide as possible - in my case f/2.8

ISO: This is going to be the variable - I start at 6400 and reduce it if its possible, however the majority of my Astro images are all at 6400. Some of you reading this who are familiar with using a camera in daylight situations will likely baulk at the idea of using your camera over 1600 ISO let alone over 3200 ISO - fret not, the normal guidelines of ISO in relation to how noisy your image gets are completely different when shooting at night - if you want to go in-depth on this topic to better understand - there is a complicated yet detailed and interesting article on this here but rule of thumb:

A higher ISO will increase the brightness of an image
A higher ISO will decrease the total dynamic range of the image
And, in many cases (like astrophotography), a higher ISO will actually decrease the visible noise

White Balance: You can use the cameras Auto WB settings, however I do prefer to manually set this to a K (Kelvins) number so I get consistent results - My go to is often 3900K which is relatively cool, you can go to 4700 or somewhere in between if if you want this to appear warmer but you will be able to adjust and play around with this in post.

Manual Focus: Autofocus systems unfortunately do not work at night and you will need to switch your lens to manual focus - finding the correct focus point is not as easy as it sounds - you cant just turn your focus ring to infinity and hope for the best - you will need to start around the infinity mark on your lens and take test photos, check focus by zooming up on the camera LCD and adjust from there to find focus. I find that by dialing in an extremely high ISO number such as 12800 and allows you to reduce your shutter speed and take fast test photos to obtain sharp focusing and then change back to the correct exposure settings once you have found focus.

Tip: Take a photo with your phone of the focus point on your lens, this will allow you to obtain focus far faster in the future if you have a reference point.

Self Timer: Unless you have a remote shutter release - please use a self timer of at least 2 seconds or longer to eliminate camera shake when you press the shutter button. The other handy feature of this (on most cameras - some may take a bit of digging to find) You can use the self-timer function to take up to 9 photos consecutively - this is extremely useful for 'Stacking' which is a post-processing method I will cover shortly.

Typical Image Settings Summary:

SS: 25 Seconds
ISO: 6400
Aperture f/2.8
WB: 3900K
Manual Focus
Self Timer on 2 Second Delay - x9 Images

Post-Processing

This is arguably one of the most important aspects of Astrophotography. You need to spend quite some time processing these images and the possibilities here are seemingly endless, I have barely scratched the surface in terms of what is possible and will show you some basic methods I have found that work for me.

Stacking

This is a processing technique that is unique to Astrophotography and is something that once used you simply cannot go back. Instead of taking a single exposure and editing that, you take multiple images at the same time (as many as you want, more is better - although you will reach a point where the file size is impractical) and blend them together in post using programs that are designed to do it automatically, there are many to choose from - this is called 'Stacking'.

What this does, in laymans terms, is dramatically reduces noise, increases overall image quality and smoothness and ultimately gives you far more data to work with. This allows you to make aggressive adjustments to really enhance the milky way and make it stand out while still retaining image quality and detail.

The program I use is called Sequator156 and is free to download, there are multiple other options out there and you can also use Photoshop although I find this more complicated than Sequator.

The below images are an excellent example. On the far left is a completely untouched image straight from the camera - this is what you will be seeing on camera at the time of shooting.

In the middle is a single exposure image I have edited to the best of my ability. This is still a great image, and is definitely the result of some exceptionally clear skies, no moon and very little light pollution.

On the far right - you see an image that I have applied 'Stacking' to. The difference is immediately obvious.

In this case it was 18 versions that I took at the time, of the image on the far left and then edited in a similar manner to the single exposure in the middle but it has allowed me to retain far more depth in the shadows, colour rendition, detail and the overall 'pop' of the Milky Way is drastically better. On top of this, when viewed blown up or zoomed up, the quality of the stacked image is far higher.

So once you have put all of your raw images through the stacking software and it has produced a TIFF file, import this into Lightroom or Photoshop/Adobe Camera Raw - for this example I am going to use Lightroom - it will look something like this:

Then, using the Masking (Shift+W) tool in Lightroom you can begin to edit parts of the image - show L-R I firstly like to edit only the sky, using the 'Select Sky' function you can automatically select just the sky and make adjustments to bring out the milky way. I have shown the slider adjustments I made on this particular mask - you may need to open this up larger to see the sliders. Once I have done that I then apply a radial mask to just the actual Milky Way itself, typically upping the exposure, dehaze, saturation and clarity a bit, just to make it pop a little. Once the sky is looking great you can then mask the foreground and play around with that.

After the masking I then make some adjustments to the image as a whole - largely adjusting the colouring of the image which is something purely personal and you will find your own style and what you like. the HSL panel shown in the middle is really helpful as well as experimenting with the Red Primary and Blue Primary Calibration panel, this can really help the finishing touches of the image. Lastly, some basic adjustments to balance the exposure and help it pop with the main exposure sliders finish it off.

You then should have a finished image that looks like these below, these have all been edited in this exact same manner.

These are all taken at Birdlings Flat (Just outside of the main Christchurch City light pollution) around 9pm in July 2022 - all are x18 Image Stacks - shot on a Nikon Z6ii with a combination of a 17-35 2.8 and 24-70 2.8 lenses.

The 17mm wide angle shot (Image 4) was shot at 25 sec, 6400 ISO and f/2.8

The 24mm shots (Image 1 and 3) were 20 sec, 6400 ISO and f/2.8

While the 50mm shot (image 2) was 10 sec, 6400 ISO and f/2.8 except this utilized a 27 image stack to retain quality and detail over such a short exposure time.

Some bonus Astrophotography from the last 2 years

Glossary

Astrophotography: The practice of taking photos of the night skies, commonly of the Milky Way
Light Pollution: A side effect of industrial civilization - the result of excessive artificial light that effects out ability to the night sky clearly
RAW: An uncompressed image format that carries a lot more data than a traditional JPEG file allowing flexibility in post processing
Focal length: Effective lens length
Exposure time: How long light is allowed to hit your sensor for, dictated by how fast your shutter speed is
Shutter Speed: How fast your shutter opens and closes - your exposure time
Aperture: the adjustable opening in your lens dictating how much light hits the sensor and your depth of field
Bulb mode - a shutter speed setting in your camera allowing it to be open for any length of time
ISO: Your cameras sensitivity to light. Carried over from the film world, in the digital age this is now adjustable rather than fixated on the film you were using
Noise: Grainy, loss of quality, can often be the result of high ISOs if used in the wrong setting
Kelvins: (K) Colour Temperature - Changes your White Balance
Stacking: Post-processing method of combining multiple images
TIFF File: Large format uncompressed image file that retains all edits and data, exported by Photoshop, Lightroom and similar programs
HSL: Hue, Saturation and Luminance

Footnotes

There are many ways to do things and this guide is simply the way that works for me, not necessarily the best way to do things. I suggest experimenting and finding workflows that suit you best.

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FootNotes

There are many ways to do things and this guide is simply the way that works for me, not necessarily the best way to do things. I suggest experimenting and finding workflows that suit you best.