What kind of lens do you need for astrophotography?

Astrophotography has many different faces. You may choose to shoot the Milky Way against a suitable backdrop, you may choose to photograph nebulae or galaxies with a camera and a lens or you might shoot the planets or moon just using your camera. Any of these will require a good quality lens that will enable you to take the best possible astrophotos. On this page, we will look at what kinds of lenses are best for astrophotography.

The kind of lens you use for astrophotography is determined by factors like the type of target, the level of light pollution in your location, and the budget you have. Small and distant targets require a telephoto lens of at least 350mm and widefield astrophotography a lens between 17mm and 150mm.

As we look deeper into this question we will consider how your target, location, and budget affect the choice of lens for astrophotography. You will also begin to understand what features you will need in lenses that you use for astrophotography. What follows is based on my experience using different lenses with a DSLR camera to shoot both Milky Way and Deep Sky Objects.

Before we move on, here is my guide to the best DSLR cameras for astrophotography – check them out!

How to Choose a Lens for Astrophotography

When I wanted to use a lens specifically for taking astronomy pictures, I first decided what I wanted to photograph. My first choice was to try to photograph the Milky Way with the camera I already had, a Canon 600D. I knew that this would require a widefield lens and all I had was a lens that adjusted between 17-85mm that came with my camera. So I went with this lens.

At first, I didn’t know which setting to use exactly so I experimented but basically I used the low setting of 17mm for the Milky Way and the upper level of 85mm for deep sky objects. What kind of results did I get, check some of my photos below to find out.

Now looking at these two photographs, I think the processing and my imaging techniques were still in their early days and I know my photos would be better now if I reprocess them, but still, you can see a lack of real detail and clarity in both pictures. Why?

The lens I used has a low setting of F4.0 which means this lens is not absolutely suited to high-quality astrophotography as it lets in less light than other lenses. We’ll discuss more about this F number in the next section and why it matters so much for any lens you use whilst taking photos of the night sky. There are a number of other problems with this lens which I will also point out in this article and hopefully, this will help you to choose a good quality lens that will help you to take excellent astrophotos.

What makes a Good Lens For Astrophotography?

There are several features of a good quality lens for astrophotography. They include these:

• A low F-number preferably below 3
• The field of view of the lens in mm.
• Possibility to adjust the F-number
• Fine focus control
• Ability to photograph stars with no halo
• Reputable manufacturer

Let’s take a look more closely at each of these above features and try to understand what they are and why they are important for nighttime photography.

F-Stop or F-Number of a Lens

What you need to know about the F-number of a lens and how it affects your astrophotography, is that it indicates how much light will pass through the lens and reach the sensor of your camera. For low-light photography, we need as much light as we can get from the distant and dim objects in the dark night sky. Therefore, a lens with a low F-stop is important.

Any astrophotographer who is looking to buy a good lens would be considering a lens of 3 or lower as a good level for a lens. Anything higher will block out valuable light and require longer exposures. In general, very low f-numbers such as 1.2 or 1.8 are more expensive. Those in the range of 2-3 are cheaper but can still give great results. To learn more about F-stop click on this link.

Field of View

When we are trying to compose a shot and frame it we need to consider the field of view of the optics we are using. My telescope has a field of view of approximately 650mm when I use my Canon DSLR at prime focus (this means I do not attach a lens to the camera but the telescope acts as the lens).

The field of view allows you to understand what your image will look like of any target in the night sky. For example, comparing my telescope’s field of view to that of a 300mm lens means that my telescope will have twice the magnification of the 300mm lens. In other words, the lens will see about twice as much sky as the telescope in the same image taken with the camera. The lower the lens FOV in mm, the wider its field of view. This is why when photographing a panorama of the sky including the Milky Way we need to use a lens of 17-30mm or so to get the widest view possible.

A telephoto lens of 600mm or more can actually replace a telescope when attached to a camera, however, a high-quality telephoto lens capable of being used in astrophotography will probably be more expensive than a telescope. This is why rather than buying an expensive lens many including myself prefer to use a telescope for closer views of deep sky objects.

According to Schedler (in Ratledge (Ed.), 2005), a lens between 20 and 300mm should be sufficient to photograph nearly all of the deep sky objects in the sky.

Can you adjust the F-Stop?

It is very helpful to be able to adjust the F-stop and the reason is that sky conditions change and your target may be brighter or fainter. By adjusting the f-stop to a higher level we can cut out light coming from light pollution or a bright moon. By using a lower setting we can let more light in and shorten exposure time. For the moment, I see no reason to use lenses lower than about 2.8 which is the best I have because I can always increase exposure time in darker locations. It is not worth the cost of having a lower Fonumber lens just to save exposure time, but this is my choice.

Some lenses do not allow you to adjust the f-number and this is a factor to consider when choosing a lens.

Fine Focus Control

Focus is an extremely important thing in astrophotography. Once or twice I spent all night imaging only to find upon closer inspection that my stars were out of focus ever so slightly. I had to throw away all those photos and that experience has made me check and double-check my focus before starting.

When using a lens you want fine control, such as that on my Samyang 135mm. It allows me to finely tune the focus and it doesn’t drift in the night. Other lenses I have tried need to be taped into position so the focus doesn’t move during the night.

Never trust the infinity setting on your lens, always check on something far away or better, on a bright star. Never get a lens if you are not sure the focus is reliable.

How Good are the Stars?

Some lenses add a halo around the stars. Sometimes I have seen a red halo around stars and one of my lenses even was unable to shoot crisp stars. This makes focusing very difficult and also can ruin your images.

It’s a good idea where possible to ask others about a certain lens, perhaps visit and ask in a forum or try the lens before buying it.

Who is the Manufacturer?

Most lenses are manufactured by Canon or Nikon and these are recommended brands for obvious reasons. Check out this post I’ve written – which is better Canon or Nikon? Don’t forget, if service is necessary at some point, it is best to have a well-known manufacturer’s lens. Chances are that you will be committed to buying a lens from a certain manufacturer because of the camera you are using. Different manufacturers’ lenses are rarely compatible.

The Lenses I Have Used and My Results

I have three lenses I use for astrophotography. They are as follows:

• Canon Zoom Lens EF 16-35mm Ultrasonic F2.8
• Canon EFS 24mm F2.8 STM
• Samyang 135mm F2.0

I use the two Canon Lenses for widefield shots and Milky Way. I use the Samyang for mainly Deep Sky Objects. I have had success with all of these lenses and as you can see they all have F-stop lower than 3. The advantage of such lenses is that they are not only suitable for astrophotography but can be used for general photography also.

So what kind of results have I had with these lenses?

I took the Canon Zoom Lens EF 16-35mm Ultrasonic F2.8 to Bali and took a series of images of the Orion nebula and the Horsehead Nebula. As I didn’t have a tracker or telescope mount, I used a normal camera tripod and took 5-second sub-exposures. Over two nights I got a total of 450 photos and stacked them together to get a wonderful widefield shot of these famous nebulae. The result was very pleasing!

You can see in this image that even when taken at an exposure of just 5 seconds the stars are elongated. I was quite surprised at this.

Nevertheless, I was quite happy with this image. What do you think?

I have also taken a number of shots with my Samyang 135mm. These shots include a great image of the Pleides which I include here. The dust associated with this star cluster showed up really well but Pleides was quite small in the field of view.

One thing I think you can see here if you look closely is the red halo around the stars. With a perfect focus, this might have been less but this is what I see with this lens. I don’t think it is a problem, do you?

Also, it is possible to remove such a halo from stars in your post-processing so that this should not be a problem in your final image.

Overall, I think this is a great image and I really like this lens. It is extremely popular in the astrophotography community.

I would recommend this 135mm lens if you’re looking for something to photograph deep sky objects at this scale. It also gave me incredible close-up shots of the Milky Way which was interesting.

What Lenses do the Experts Recommend?

The first expert in astrophotography is Alyn Wallace, who mainly shoots Milky Way shots with landscapes. He recommends the use of Sony Lenses, especially the following:

• Samyang 14mm F2.8 – affordable, good performance
• Sony G Master F1.8 same price has half the weight and better performance. Also fantastic for photographing star trails.
• Sony 24mm F1.4 G Master – lets lots of light in, and takes great pictures. This is one of Alyn’s favorite lenses (according to his youtube channel).

Delta astronomy, via their youtube channel, recommend these lenses:

• Rokinon Samyang 14mm F2.8 – (many lenses from Rokinon are also available with the Samyang brand but they are identical).
• Rokinon 24mm F1.4 – at this f-stop this lens will let lots of light in!
• Tamron 150-650mm – not the best but reasonably priced, sharp stars, and good colours. At the top end, this is similar to a telescope with a field of view of 650mm.

Trevor Jones, from AstroBackyard.com, is one of my favourite YouTubers in this field. I really respect his views and opinions. He recommends and has used the following lens for astrophotography:

• Samyang Rokinon 135mm F2.0 – so good and affordable. I can also vouch for this lens as I have it and love it too!

CameraGurus, popular on youtube for their professional photographic reviews, recommend the following lenses:

• Canon EF/M 22mm F2.0 STM – no chromatic aberration.
• Canon EF 50mm F1.8 STM – clear and sharper images and stars.
• Canon EF 16-35mm F4 – amazing images of space!

Conclusion

Depending on what kind of astrophotography targets you plan to photograph, the three lenses I have are reasonably good and I do recommend them. However, there are many choices that also depend on how much money you want to spend on a lens. I wouldn’t advise any beginner or inexperienced photographer to waste lots of money on a camera lens that is too advanced, this will not help you to improve. So, how can you start doing astrophotography cheaply? – Click to find out.

I prefer to use a telescope rather than buy an expensive telephoto lens, however, one advantage of using a lens is that it is so much more portable. I can’t really transport my telescope equipment with me on my travels but a camera, lens, and tripod can go anywhere with no risk of damage.

It is so handy to just be able to pick up a camera and tripod and use a good lens to shoot on the go. As we have seen you need to give some thought to your choice of lens before buying. You don’t want to be disappointed by the results after spending a big chunk of change!

References

Covington, M.A. (2018). Digital SLR Astrophotgraphy. Cambridge University Press. Link to Book Description.

Ratledge, D. (Ed.). (2005). Digital Astrophotography. Patrick Moore’s Practical Astronomy Series. Springer. Link