In this guide we’ll cover the basics of taking astro-images with a DSLR, camera lens and tripod. We’ll also take a look at using a simple tracking mount to take longer exposures.

Skill Level: Beginner

Objectives:

Required Equipment:

Introduction

Whilst it is certainly true that astro-imaging can be an expensive hobby, you may already have all the equipment you need to get started. If not you can acquire it relatively cheaply either new or second hand. Indeed, some of the best astro-images in glossy magazines are taken with nothing more than a camera, lens and tripod.

What You’ll Need

Whilst it can be tempting to rush out and buy a load of new equipment, we’d really caution you against doing so as it is easy to make very expensive mistakes. Take stock of what you already have and give that a go first; most of us have a camera and lens in a cupboard somewhere, and maybe even a telescope gathering dust. You’ll be surprised at what you can achieve with the most basic of equipment, and members should take advantage of the advice on offer in the Imaging Wednesdays group before pressing the ‘buy’ button!

Camera: Whilst some of the newest high-end smartphones have night photography modes that can capture the stars, it’s a bit of a gimmick and a DSLR or mirrorless camera with interchangeable lenses is the best starting point for astro-imaging. They’re relatively inexpensive (especially second-hand) and you will be able to attach it directly to a telescope as you progress further with the hobby.

If you already have a camera, see what you can achieve with it before you spend any money! If you do need to buy a camera, most imagers start out with a Canon EOS or Nikon DSLR. Whilst you’ll be using the camera manually in this guide, most newer Canon and Nikon models can also be controlled by software on a laptop which will come in useful later in your journey.

You don’t need the top end latest model; the lower-end consumer models can be had new or second hand for a few hundred pounds and will be more than satisfactory to get started.

Lens: Consumer models of DSLR and mirrorless camera are often sold complete with a “kit lens”, typically an 18-55mm zoom lens. Again this is more than satisfactory to begin with. If you need to buy a lens, bear in mind that they tend to be specific to a camera manufacturer, e.g. Canon cameras require a lens with a specific Canon fitting (other manufacturers such as Sigma and Tamron also make lenses for Canon, Nikon, etc. but again a specific lens will only fit one manufacturer’s camera models).

Lenses have a focal length specified in millimetres, with lower focal lengths being less ‘zoomed in’ than higher ones. As a beginner you’ll want to start with a lower (“shorter”) focal length – less than 50mm. For example, when fully zoomed out, the 18mm focal length of the Canon kit lens is ideal. This will fit more of the sky in to the field of view and also allow you to take longer exposures, as we’ll see in a bit.

Lenses also have an f-number (also called the focal ratio, f-stop or simply “stop” for short). This relates to to the size of the lens itself (the “aperture”) and the focal length. Simply put, the lower the f-number, the quicker the lens will capture an image, so an f/2 lens will capture an image more quickly than an f/5 lens. Most lenses allow you to change the f-number (within limits), so don’t worry about this too much for now as we’ll explain the best settings to use in a bit.

Tripod: You’ll need a tripod to be able to aim the camera at the sky and keep it steady whilst taking your images. A good quality tripod will be much easier to adjust. It will also be more sturdy and less prone to shaky/blurry images, but good models can be quite expensive. Cheaper tripods can be improved slightly with a few tricks though:

  • Only extend the legs as far as you need to in order to see through the camera viewfinder. If you have a solid garden table or similar try standing the tripod on it rather than extending the legs fully as it may be more stable.
  • Most tripods have a central point where the legs or the spreader holding the legs apart meet. You can tie the top of a length of cord (ideally elasticated) here and then tie the bottom to a brick, block or bag of sand resting on the ground between the legs. Don’t make the cord so tight that it causes the tripod to buckle or tip over, but a bit of gentle downward pressure will stabilise the tripod and dampen any vibrations more quickly.
  • Miniature tabletop tripods are a similar price to and a lot more stable than cheap full-sized ones, but you’ll need to sit them on a solid table, wall or car bonnet/roof.

An intervalometer or remote shutter release (optional): The very act of pressing the shutter button on the camera will cause it to wobble and vibrate. Whilst you can get around this using the camera’s delay timer to take images, a cheap remote shutter release (wired or wirless for more modern cameras) can be obtained from Amazon or eBay for a few pounds. Better yet, a cheap “intervalometer” will allow you to program a series of exposures to be taken without needing to touch the camera.

A tracking mount (optional): In order to take longer exposures and capture fainter objects, you’ll need the camera to track the sky as it rotates. If you have a telescope and tracking mount you can attach the camera “piggy back” to the telescope to take longer exposures with the lens (rather than shooting through the telescope itself). If not, there are a number of simpler tracking mounts available that are designed to fit between the camera and camera tripod. Examples include:

  • Skywatcher Star Adventurer and Star Adventurer Mini
  • Vixen Polarie Star Tracker
  • iOptron SkyGuider Pro

Prices for these vary from £200 to about £500, and you will need to add a camera tripod if you don’t have one, and in most cases a “ball head mount’ to enable you to aim the camera. At the lower end of price range, these are a cheap way to progress in your journey, but at the top end it may make more sense to consider a full-sized telescope mount unless you need something very small and portable.

Taking Star Trails

The simplest technique in astro-imaging is to capture star trails. In order to do this, you need to aim the camera at the sky, focus it and open the shutter for a long period of time. You do need a remote shutter release or intervalometer for this technique to work, otherwise you’ll be limited to the camera’s maximum long-exposure length (typically 30 seconds). As the Earth rotates on its axis, the stars will move across the field of view creating streaks of light of different colours and brightness.

Aperture:f/4 or lower
Shutter speed:Bulb Mode*
ISO:800

Steps

  1. Firstly, you need to set your camera to Manual (“M”) mode. This will normally be done using the large dial on top of the camera. Manual mode gives you complete control over all of the camera settings which is essential for astro-imaging as the various (semi-)automatic modes won’t usually work well for us.
  2. Next, if you are using a zoom lens, set it to the lowest focal length to give the widest field of view and lowest possible f-stop.
  3. Now change the aperture to the lowest f-stop that the lens allows, ideally f/4 or lower. We may need to change this after experimenting, but this will give the brightest image to start with.
  4. Set the shutter speed to Bulb (“B”) mode. This will keep the shutter open for as long as the remote shutter release or intervalometer is pressed.
    If you don’t have one, set the shutter speed to the maximum the camera allows. This is typically 30 seconds which will only produce very short star trails, but you don’t want to stand there holding down the camera shutter button for a long time. Not only is it uncomfortable, it will make the camera wobble and shake ruining the image.
  5. Finally set the camera to ISO 800. This should give a reasonably bright image on the camera screen, but as with the f-stop we may need to adjust this later.

You’ll need to consult your camera manual for instructions on changing the f-stop, shutter speed and ISO when it is in Manual mode. Each step usually involves pressing one or more buttons and turning a wheel or dial that varies between camera manufacturers. Once you’ve figured out the right combinations, make a note of them in a small notebook as you’ll need to change these settings frequently as you progress.

Focusing

When taking an astro-image, the most important thing is to make sure the camera is in focus. You can do a lot to fix problems with an image in programs like Photoshop, but there is no software that can bring an image into focus. Double and triple-checking for good focus will save you a lot of wasted time and frustration later.

As with the other settings, you can’t rely on the camera’s auto-focus function when taking an astro-image. It may work for images of the Moon but that is by no means guaranteed, and definitely won’t work for stars, planets or anything else astronomical.

  1. Set the camera to manual focus mode. You usually do this by sliding a little switch on the camera lens from “AF” (Auto Focus) to “MF” (Manual Focus). Don’t forget to set it back to AF when you’re done otherwise your holiday snaps will turn out rather blurry.
  2. Set the lens to infinity focus by turning the focus ring on the lens, which is usually in front of the focal length ring on a zoom lens. Some lenses have focus distances marked on the focus ring, with infinity focus marked with a “∞” symbol. Other lenses don’t have any markings so you’ll have to figure out roughly where this is by looking through the camera viewfinder at a really distant object during the day (e.g. a tv aerial a few hundred metres down the road).
    If the focus ring won’t turn, check that the lens is in MF mode, as the focus motor will lock it in place when in AF mode.
  3. Now take a short exposure of a few seconds at most so that the stars don’t trail in the image (see Rule of 500 below). Using the screen on the rear of the camera, zoom in on a bright star in the image. If it looks trailed (like a short dash or streak) then take a shorter exposure. Check whether the star is sharp and in focus, and if not slightly adjust the focus ring and try again until it is.
    If you can’t see any stars, increase the ISO setting and take another exposure, or try a slightly longer exposure whilst keeping it short enough to avoid trailing. Remember to set the ISO back to 800 once you have achieved good focus.
  4. You can now take your first star trail exposure – start with one minute and see what you get, increasing to two minutes, etc. Unless you have very dark skies, exposure length will be limited by the amount of light pollution nearby. The sky background will become increasingly bright with longer exposures. You can try reducing the aperture (using a higher f-number) and/or decreasing the ISO to see if you can take a longer exposure.

Try pointing your camera at different parts of the sky to see what effects you can get. The classic image is to point the camera directly at the North (or South) celestial pole so that the stars trail in a circle around the centre of the image.

Bear in mind that you will often see other streaks in your image caused by passing aircraft lights. You’ll also often capture brighter satellites and perhaps even the International Space Station. You may consider that these intruders add to or detract from your images depending on your personal outlook!

You can try enhancing the image in Photoshop or Affinity Photo by changing the brightness and contrast of the image to dim the sky and bring out the stars, or increase saturation of the highlights to bring out the star colours more. You can also take multiple star trail exposures one after another and “stack” them using layers in a photo-editing program or use Sequator to combine them.

Constellation Images

Next we’ll look at taking images without trailing the stars. This can be done with or without a tracking mount. When properly set up, a tracking mount will follow the stars as the move across the sky avoiding trailing. If you do not have a tracking mount you will need to keep your exposure length short enough to avoid star trails.

Aperture:f/4 or lower
Shutter speed:Use Rule of 500
ISO:800

Rule of 500

The Rule of 500 tells you how long you can keep the camera shutter open without creating noticeable star trails. Simply divide 500 by the focal length of your lens to calculate the maximum possible exposure time. If the figure you get is not a whole number remember to round it down.

For example:

24mm lens = 500 ÷ 24 = 20.8 seconds = 20 seconds rounded down.

Steps

In order to take a constellation image, we proceed exactly as we did for Star Trails, except we limit the exposure length to the Rule of 500.

  1. Set the camera to Manual (“M”) mode.
  2. Set the focal length if using a Zoom lens (lower values give wider fields of view)
  3. Set the shutter speed to the maximum time allowed by the Rule of 500 for the focal length of the lens.
    If you’re using a tracking mount, you can of course expose for longer without trailing so try increasing the exposure time in steps to see what works best for you.
  4. Set the ISO to 800.
  5. Focus the lens as described above.
  6. Take an exposure. Ideally do this using a remote shutter release or intervalometer to avoid camera shake.
    If you do not have one, you can use the camera’s “Self Timer” function. This will delay opening the shutter for a defined number of seconds after you press the shutter button, thus allowing any vibrations you caused to die down. Consult your camera’s manual to learn how to use the Self Timer.
  7. If the stars appear dim, try increasing the ISO. Conversely if the sky is too bright due to light pollution, try reducing the ISO and/or exposure time.

Now you are set up, why not try an image of the Milky Way? Bear in mind that your focusing will need to be spot on. Aiming the camera can be a bit of a challenge as you usually can’t see too much through the viewfinder. Just point the camera roughly in the direction you desire, take an exposure and adjust repeatedly until you have framed the subject correctly.

The techniques we have described here can also be used to capture brighter objects such as comets when they occasionally grace our skies.

Your images will certainly benefit from tweaking in a photo-editing program like Photoshop or Affinity photo to darken the sky and brighten the Milky Way and stars.

You can take multiple exposures of the same subject and combine them in a process known as “Stacking” to create a better image. This can be done using the layers feature in Photoshop of Affinity Photo, but it works better in specialist astro-processing software (e.g. Deep Sky Stacker, PixInsight or Astro Pixel Processor). See our other guides for more details on stacking multiple images.

Mirror Lock-Up

When you press the shutter release you will cause the camera to shake, which can be cured by using the self-timer or a remote shutter release/intervalometer. If you are using a DSLR (rather than a mirrorless camera) part of the shutter’s action will also cause the camera’s internal mirror to flip up out of the way of the sensor, causing yet more camera shake.

To get around this, most DSLRs have a “Mirror Lock-Up” function which flips the mirror out of the way and leaves it there until turned off again. You can continue to use the camera as normal whilst the mirror is locked up, but it does prevent you looking through the camera viewfinder which isn’t a problem for astro-imaging. Check your camera manual for details of how to turn mirror lock-up on and off.

A Quick Word About ISO

The camera’s ISO setting determines how bright the image will appear on the screen, with higher ISO values making the image brighter. Thus it is tempting to imagine that higher ISO values make the camera more sensitive to light.

That was certainly the case in the days of film cameras. Loading film with a higher ISO number would make the camera more sensitive allowing the use of shorter exposures or photographing in darker conditions. In a modern digital camera, the sensor chip has the same sensitivity to light regardless of the ISO setting.

The ISO setting determines how much “Gain” (amplification) is applied to the image captured by the sensor before it is displayed on the screen, thus mimicking the behaviour of film ISO values.

Using a high ISO value can be useful as it will make the image appear brighter on the camera screen (e.g. when framing your subject or focusing), but there is a risk that you will overexpose really bright objects like the planets, Moon or a bright star. Conversely if you use a low ISO value you can always fix dim images later in a photo-editing program; you won’t “lose” any details by using a low ISO.

Taking Simple Moon Images

The Moon is a great subject for beginning astro-imagers as it’s really bright and thus easy to find with the camera. It is possible to take a good Moon image with a camera and lens, but in this case longer focal lengths are better so that we can zoom in and see more of the features. The Moon is very bright though, so you’ll want to use different settings.

Aperture:f/11 to f/16
Shutter speed:1/125th to 1/250th of a second
ISO:100 to 200

Steps

We proceed very much as before:

  1. Set the camera to Manual (“M”) mode.
  2. Set the focal length if using a zoom lens, but this time try a longer focal length to zoom in more and see the details. Bear in mind that at higher focal lengths the Moon will move out of the field of view more quickly as the Earth rotates.
  3. Focus the lens as described above. You’ll need to focus a zoom lens after you set the focal length (zoom) as the focus point changes at different focal lengths. You may find it easier to focus on a star first (using the ISO and shutter speeds as described in focusing above) and then point the camera at the Moon. Alternatively you may find it easier to focus directly on the Moon itself using the exposure and ISO settings described below.
  4. Set the shutter speed to approximately 1/125th to 1/250th of a second.
  5. Set the ISO to 100 or 200. You’ll need to take some test exposures to find the best values for ISO and shutter speed.
  6. Take an exposure. Ideally do this using a remote shutter release or intervalometer to avoid camera shake.
    If you do not have one, you can use the camera’s “Self Timer” function. This will delay opening the shutter for a defined number of seconds after you press the shutter button, thus allowing any vibrations you caused to die down. Consult your camera’s manual to learn how to use the Self Timer.
  7. Zoom in and check you can see the details and that they are in focus. Experiment with focusing and different shutter speed / ISO combinations. It’s worth trying multiple experiments as you’ll only be able to truly judge what combination is best when you view the images on your computer screen later.

Using a remote release/intervalometer and mirror lock-up is even more important when taking such short exposures, as there is no time for camera shake to die down.

It is just about possible to capture the Moon and the background stars in a single exposure, but usually the stars will be under-exposed and dim or the Moon over-exposed and washed out. The images you see in glossy magazines containing the stars, Moon, Milky Way and a fabulous landcape all perfectly exposed are “Composites”. The imager will take multiple images with different exposures appropriate for each element, and combine them later in Photoshop or Affinity Photo using Layers and Masks.

As you proceed, make notes of what you have done; both what works and what doesn’t. Your notes will be a good place to start from next time which may be in a few weeks due to the typical British weather.

Using a Tracking Mount

If you have a tracking mount, you can go after more challenging targets as your exposure length will tend to be limited by local light pollution rather than the need to avoid star trails. When using a tracking mount there are a few important considerations:

  1. If you have a simple Alt-Az tracking mount, you can expose for somewhat longer than suggested by the Rule of 500 without star trailing. That said, the camera will remain in a fixed orientation with respect to the horizon, whereas the stars appear rotate with respect to the horizon as they move from East to West. E.g. Orion rises lying on one side, stands upright when due South and sets lying on the other side.
    This means that stars in your image will begin to suffer from “Field Rotation” after a certain exposure time. In other words they will begin to form little curved arcs rather than remaining as round points of light. Field rotation becomes visible sooner near the celestial equator than near the celestial poles, and also becomes visible sooner the longer the focal length of the lens.
    Whilst it is possible to calculate the maximum exposure time in this scenario, it is probably easier to experiment a bit.
  2. An equatorial tracking mount is a much better option for astrophotography. The mount’s main axis of rotation is “Polar Aligned” to the Earth’s axis of rotation, and thus the camera’s field of view rotates in the same way as the sky and so eliminates field rotation.
    Ensure the mount is level, as this makes polar aligning it much easier. Polar aligning the mount is described in the mount manual and in our other guides. You don’t need perfect polar alignment, but the better you do, the longer you can expose for without visible field rotation.
    If you have a GOTO telescope mount you will also need to perform a star alignment as described your telescope manual. With a simple tracking mount (star tracker or telescope mount), you just need to aim the camera lens at your target, without changing the polar alignment.

Steps

It is difficult to give definitive advice about the right settings for the wide variety of objects in the sky, but here are some suggestions for objects you can capture with a camera lens to get started with:

Star ClustersE.g. Beehive Cluster, Double Cluster in Perseus, Pleiadies
Aperture:f/4 or lower, short/medium focal length
Shutter speed:BULB, experiment from 1 to 5 minutes
ISO:800 and up
GalaxiesE.g. M31 (Andromeda Galaxy)
Aperture:f/4 or lower, longer focal lengths
Shutter speed:BULB, experiment from 3 to 10 minutes
ISO:800 and up
NebulaeE.g. Orion Nebula
Aperture:f/4 or lower, short to long focal length
Shutter speed:BULB, experiment from 3 to 10 minutes
ISO:1600 and up

None of these settings will be exact and you will need to experiment with exposure and ISO and remember to make a notes as you go along. The rest of the capture process is exactly as described in the Constellation Images section. All of these objects will benefit from further processing in Photoshop or Affinity Photo, and they will also benefit from stacking as described in our other tutorials.

That’s it for now, clear skies and we hope your neighbours do not install mini searchlights in their gardens!

Next Steps

Once you have mastered the basics, you should look at other tutorials on our web site and elsewhere on topics such as:

  • Processing astro-images (Photoshop, Affinity Photo)
  • Stacking star trails (Photoshop, Affinity Photo, Sequator)
  • Stacking constellation, star cluster, galaxy and nebula images (Deep Sky Stacker, PixInsight, Astro Pixel Processor)
  • Controlling your camera with a Laptop (BackYard EOS, BackYard Nikon, APT, etc.)
  • Focusing with a Bahtinov Mask

Contributors (Words): Andy Styles, Ian Lauwerys
Contributors (Photos):