Astrophotography - an Introduction
During 2020 (where we all discovered new hobbies, got fit, and had remarkable weather and clear skies) I found astrophotography a very rewarding way to improve general photography skills, understanding, and processing techniques. At the same time, I gained an appreciation for the vast array of subjects in the night sky to take photographs of; the moon, planets, constellations, shooting stars, comets, satellites, the milky way, and nebulae/ deep sky objects (DSO) e.g., Orion or Andromeda.
For some reason I decided to try and capture star trails in my back garden. Admittedly my garden doesn’t have the best foreground, but it was the technique I wanted to understand.
I was very happy with this image, and it is the one that encouraged me to see what else I could capture in the night sky. I thought I’d share what I’ve learnt so far based on my experience, covering some basic considerations, equipment and helpful tools to make the most of clear night skies.
For me astrophotography is a broad-brush term for anything in the night sky. I would break it down into three categories, each requiring different technique, processing, and possibly equipment:
Nightscapes – wider images of the stars and constellations including the landscape
Deep Sky Objects (DOS’s) – distant planets and nebula
Moon Shots – these can be close ups or including landscape subjects that make the moon look closer than it appears.
I’ll cover the specifics of these three categories in separate blogs.
Taking photos of any night sky subject requires planning, equipment, technique and a degree of photo processing, the amount of which will depend on the subject.
The earth rotates, stars and planets move, and we live in Britain, so cloud is a major spoiler. This makes planning the most important aspect of astrophotography to give the best chance of capturing a good image. I consider the following when planning:
Some night sky objects aren’t visible all year round e.g. the Orion constellation can only be seen in the Northern hemisphere from November to mid-March
Is it a new moon or a full moon? A full moon brightens the sky and may mean some of the stars or Nebulae won’t stand out as much. A new moon is best for astrophotography, but anything less than 40% full will increase your opportunity
What time will the subject be visible? Whilst the milky way is visible most of the time, the bright core is only visible between March and October and often for only 1 hour.
clear skies or at least with minimal cloud are essential
preferably not too windy.
Night sky subjects which are nearer to the ground will be impacted by light pollution so try and find an area looking away from city lights
constellations and the moon can easily be captured from your back garden or local park
the stars and planets aren’t in the same position all year round so if you want to shoot a particular foreground location it needs to be timed with the stars position
to get the best images finding a dark sky area or looking toward an area with a Bortle rating of 4 or less will give you usable results. Bortle is a scale that measures light.
Excellent dark-sky site
Typical dark site
Rural sky (mid Wales)
Suburban sky (Broadway, Chesterton, Rollright stones, Clee Hill)
Inner-city sky (Redditch)
Bright suburban sky
Holidays can provide a good opportunity to have a night shooting the stars. Coastal or mountainous areas mean you often have little light pollution.
To help plan the right time, weather and location there are several free phone apps or websites I have used:
Stellarium - a simple to use phone app (or on web) detailing a map of the night sky with date and time. If your phone has a compass, you can see the night sky positions live to identify your subject
Sky Walk 2 - like Stellarium, but with alerts and astro news. This is useful because if you’ve noticed, the BBC always tell you about a night sky event the day after its happened
Clear Outside - a weather app which also details phases of the moon, when the International Space Station (ISS) flies over and importantly cloud cover prediction (most weather apps have this, the Met Office one is also good). Clear Outside also includes the Bortle rating for the area.
Light Pollution Map - provides a map based on Bortle ratings and an idea of where least light pollution can be found/ avoided.
Google Earth can help with Milky Way location with specific foreground interest
PhotoPills - This is a paid for app (about £10 on Android) and provides precise location planning and augmented reality (your phone needs a compass) views mostly for the milky way. But also provides several aids to ensure you have the right camera settings for your camera and lens e.g., if you want star trails or sharp stars
For camera settings, if you don't have or want PhotoPills then you can use https://www.lonelyspeck.com/advanced-astrophotography-shutter-time-calculator/ which will calculate the longest you can expose for, without the stars trailing based on your lens
A great source of inspiration and education for astrophotography is the YouTube channel by Alyn Wallace https://www.youtube.com/@AlynWallace, each month he details WITN’s (What’s in the Night Sky) and often does location VLOGs and “how to’s”.
You don’t need specialist equipment, I’ve used a DLSR/ Mirrorless, a compact travel camera and my phone to capture night sky images.
A camera with
ability to select settings manually (shutter speed, aperture and ISO)
a lens with fast aperture (preferably anything in between F1.8 and F4)
or a Smart phone with Long Exposure Night or Star modes
Lenses, if you have a DSLR a prime lens will give the best results, however a zoom kit lens like my 16-80mm F4 means I can try most astro subjects and get nice results
A focal length of anything up to 50mm (full frame equivalent) will be fine for the Milky Way, Constellations and star trails. My wide lens is 13mm but is on a crop camera so is effectively 20mm
50mm and above will allow you to get closer constellations and even some nebulae photos
A tripod - stability is essential, you are either going to have a shutter speed of 10-25 seconds or be taking lots of 1-10 second images
An L Bracket – whilst not essential it allows you to mount your camera easily in portrait position on a ball head, especially if your lens is heavy. Generic L Brackets are reasonably priced but may cover your battery or remote shutter slot when on your camera (not really an issue)
A head torch is useful to help see whilst you set up.
Depending on the lens focal length you need to establish the maximum exposure you can take that will not cause star trailing (unless that’s the effect you want). Photopills or (https://www.lonelyspeck.com/advanced-astrophotography-shutter-time-calculator/) will help with this.
Here Photopills recommends 15.45 seconds for a 13mm focal length at f2.8 on a Fujifilm X-H2s, using the more precise *NPF rule (Lonely Spec also uses this rule).
*N = Aperture, P = Pitch, F = Focal Length
ISO is the variable here and is what you adjust to refine the brightness. I generally use between 1600 – 3200 and I adjust this until I’m happy that any lights aren’t blowing out especially if there is light pollution.
Here are a few tips for any night subject:
Brighten your LCD so you can see and review your image, but bear in mind when you review your image on your PC it will be significantly darker. This is fine as you will be able to brighten it in post processing
Shoot in Manual mode
Put a 2 second timer on to avoid camera shake, or use a remote shutter release
Switch off image stabilisation/ vibration control
Focus to infinity on the lens (or use in camera live view zoom to focus on a star and manually focus until it is sharp)
Take a test shot and review, zooming in to check if the stars and the subject are in focus. If it’s too dark slow the shutter speed first and retake. Review the shot and zoom in to see any star trails have formed, if they have, increase the shutter speed and then increase the ISO instead. Repeat until happy.
If your image has foreground you may want to take a separate shot to focus and expose for the foreground specifically and then merge the shot when you process the photo with the stars focussed one.
Some photo processing software will allow you to stack images, reduce noise, brighten your image and bring out the detail. For one shot images a simple raw converter will allow you to process an image (if you have shot in raw).
In the above example I’ve only applied a few adjustments in DXO Photolabs to brighten the image. Smart Lighting is like the Whites setting in Lightroom, Clearview Plus is like Dehaze/ Clarity. I have boosted the saturation a little and lifted the shadows on the foreground.
For more complex processing or where you have foreground and stars as separately focused and exposed images, any photo processing software with the ability to add layers will do the job such as Photoshop, Elements or Affinity Photo. Additionally for star trails and nebulae you’ll take lots of images that will need to be stacked before processing and I’ll cover this in more detail in a separate blog.
Whilst this isn’t a comprehensive guide to astro photography I hope you’ve found it useful, either to decide it’s not for you, or that you might have a dabble. If you do I wish you clear skies!