What are the best camera settings for astrophotography?
Such a simple question has not a simple answer.
The quality of the sky, the specific gear you are using and the type of target you want to photograph all play a role in determining the best camera settings.
In this article, you will find little in the way of numbers: as there is not a “one-fits-all” setting combination for astrophotography, I think it’s more important to give you an explanation of the important criteria to set your camera properly.
What Are The Most Important Camera Settings In Astrophotography?
As with any type of photography, as also in astrophotography, you are aiming at getting a properly exposed image.
Exposure is depended on how much light you collect, and in photography you have three ways to control how much light you can gather:
- Lens Aperture
- ISO
- Shutter Speed
Aperture
Here in a nutshell what you need to know about aperture:
- If you are using a telescope, the aperture is fixed and corresponds to the opening of the telescope and is measured in mm or inches.
- If you are using a photographic lens, you can control the size of the aperture by opening or closing the lens diaphragm. Here you use f-numbers instead of the mm of the opening, and the lower the f-number the wider the aperture.
- The wider the aperture, the more light you can collect in a given amount of time.
You may have already got that wider aperture is better, but keep in mind that rendering the stars in the proper way (round across the frame and with little to no chromatic aberration) is not a piece of cake.
Many fast lenses (i.e., with wide aperture) show optical aberrations on stars when used at full aperture, such as coma (stars like little comets) and chromatic aberration.
If you have a lens, you may need to close the diaphragm by one stop or so. If you have a telescope you may need a corrector to solve some of the issues.
ISO
When photography was done on film, the ISO value was related to the film sensitivity to light: a film ISO 400 was 4 times more sensitive to light than a film ISO 100, thus allowing it to use a faster shutter speed in low light conditions.
In the digital era, the concept of ISO remained but camera sensors have only one native sensitivity to ISO.
Today, increasing the ISO in your DSLR does not make your camera more sensitive to light. Instead, the digital signal from the sensor is amplified accordingly to your ISO settings.
Increasing digital ISO does brighten the image, at the cost of introducing more noise and further reducing the dynamic range the sensor can see, i.e., the maximum contrast between the darkest shadow and the brightest highlight in the scene the sensor can deal with.
Shutter speed
The shutter speed controls how long the sensor (or the film) is exposed to light. This can also be used in a creative way, such as freezing a fast action or introducing motion blur in the image.
In astrophotography, one of such creative effects is star trails: the shutter stays open long enough that the motion of the stars in the night sky is recorded in the image.
In astrophotography, though, the shutter speed may be limited by seeing conditions and by the stars movement in the sky.
If you are photographing from a fixed tripod, your focal length is what limits the shutter speed and you can use some empirical rules (500-rule and NPF rule) to get the slowest shutter speed for which stars are reasonably round in your image.
In the ideal world and under an exceptionally dark sky, if you are tracking the star movements with a motorized mount (with a star tracker or equatorial mount), the precision of the tracking is what limits your shutter speed.
In reality, when you track the sky, the sky brightness is another crucial factor that may limit your shutter speed, as we will see in more details later on in this article.
What Other Camera Settings Should You Adjust?
Shutter speed, Aperture, and ISO value are part of the so-called Exposure triangle and are the pillars of photography.
But in today’s digital cameras you can change other settings too, such as White Balance and the file type of your digital images.
Let’s see what to do with the most common camera settings.
White Balance And File Type
White balance does not affect your image exposure, nor should you care about it for your astrophotography images.
White balance is only applied in-camera to the jpg, and in the way you see the image on the screen: since you always want to shoot in RAW for deep sky astrophotography, you can tweak the white balance during the editing.
In-Camera Noise Reduction: ON or OFF?
Most modern cameras have noise filters that you can apply in-camera to your images to create cleaner shots. For the most part, they only affect images saved in JPEG format.
But there is one form of noise reduction that will affect RAW images as well: Long Exposure Noise Reduction, or LENR for short.
This is not a digital filter to remove images. What it does is automatically snapping a second image with the same settings of the one you shot but without opening the shutter curtains.
Essentially, with LENR ON the camera is taking a dark frame after every image and will subtract this dark frame to the original image.
This is the essence of image calibration in astrophotography (minus bias and flats) and in theory this ensures the best possible calibration for non-cooled cameras like your DSLR.
Problem is, LENR will double the amount of time needed to complete your photographic session: it is not practical.
Better turning OFF LENR and take some darks at the end of the session while you put away your equipment.
If you want to know more about what image calibration in astrophotography is and why you should care, have a look at our guide on calibration files.
To summarise, turn OFF all types of noise reduction your camera may offer you.
Image Stabilisation: ON or OFF?
Image stabilization, whether done in-camera or in the lens, is a sensational achievement in photography and allows you to take sharp photos handheld when in low light conditions.
Of course, image stabilization can only deal with camera shaking: if your shutter speed is too slow to freeze the subject (think of a dancer on a dark scene of a theater), you still get a blurred subject.
But we are not shooting stars handheld are we?
Some cameras detect they are on a tripod and shut the stabilization OFF automatically, but many don’t do so and will try compensating for movement that is not there, thus blurring your image.
So turn image stabilization OFF when you do astrophotography.
Autofocus: ON or OFF?
Focusing on stars is a crucial step in astrophotography: fail to get your stars in focus and even the best sky will be ruined.
More often than not, though, autofocus is not the solution. Because stars are small and the sky is (hopefully) dark, autofocus will hunt forever without successfully bringing the stars in focus.
So turn autofocus OFF and rely on manual focus instead. It helps to turn your camera live view ON and magnify a bright star.
We have covered this in a detailed article the task of focusing on the Moon and the stars, but let me remind you of the three tale-telling signs your focus is good when using a DSLR or mirrorless camera:
- The more in-focus you are, the smaller the stars look in your live view
- The more in-focus you are, the more faint stars will become visible in your live view
- The more in-focus you are, the less chromatic aberration you will see around the brightest stars
Are DSLR, Mirrorless And Astro Cameras Settings The Same For Night Photography?
The main difference between mirrorless and DSLR cameras is the fact mirrorless are… well… mirrorless!
Without the mirror, there are fewer parts in motion that could create camera shake (mirror slap).
In astrophotography, though, particularly if you are tracking, mirror slap is not a big problem and nobody bothers with using mirror lockup.
In short, there is no difference in the camera settings and in the criteria to set exposure settings between different types of cameras.
Astrophotography Settings For Deep Sky Astrophotography
In astrophotography, particularly in deep-sky astrophotography, we cannot “get it right in camera”.
This is an old saying dear to hard-core photography purists, and it means that photographers should know how to use the basics of photography to create a “correct” photo in-camera, rather than relying on editing to fix their mistakes.
But in astrophotography, we cannot avoid editing and to shoot for editing.
Most Common Misunderstandings: Understanding Exposure In Astrophotography
With astrophotography becoming more and more accessible to the public, many daylight photographers are trying their luck with the night sky.
While photography knowledge is important, not all concepts can be applied to astrophotography, and this creates some misunderstandings.
One of the bigger misunderstandings of all is going after the correct exposure. In deep sky astrophotography, there is no such thing: you will never, ever, get a properly exposed image in-camera.
A common misunderstanding is about ISO: increasing the ISO does not make your sensor more sensitive to light. By increasing the ISO you simply digitally amplify whatever signal is coming from the sensor, which only has a single, native, ISO.
The downsides of high ISO are increased noise in the image, which we can deal with image stacking, as it is random noise, and a reduced dynamic range, which causes your stars to get clipped to pure white.
The key misunderstanding is that for every target, one must look for a proper set of settings, kind of like for the Full Moon with the Looney F11. This is (partially) wrong, as you must shoot for the sky brightness in your location and not for the specific deep space object you intend to photograph.
Shooting For The Sky Brightness
The sky is not pure black. Even in the middle of the ocean, far from any man-made light pollution, the Moon and the Milky Way light the sky.
A simple way to estimate the sky brightness for your location is using a visual scale called the Bortle scale. Maps such as the one shown above allows you to have a rough idea of how bright the sky is at a specific location.
With the exception of exceptionally dark locations with exceptional seeing, the sky brightness overpowers most, if not all, the deep sky objects you can photograph.
Try to get a single image “well exposed” for the target, and you will end up with a pure white image, as you clipped the whole sky.
Before continuing, it is useful to recall what the histogram is and how you read it.
The pixel’s brightness ranges from 0 (black) to 255 (white) and is shown on the x-axis of the histogram, while the number of pixels of a given brightness is shown on the y-axis.
Accordingly to the pixel brightness, we can identify 5 tonal zones on the histogram:
- Darkest tones (Blacks)
- Dark tones (Shadows)
- Mid tones (sometimes called Exposure)
- Light tones (highlights)
- Brightest tones (Whites)
Now go outside and snap a few seconds-long exposures of the night sky (avoid framing the Moon for this exercise, though) and look at the histogram.
What you will see is that the histogram is showing a single peak dominating everything: that peak is the sky brightness and what we will use to select the best camera settings for our sky.
Look carefully at the right of the peak: you should see the histogram has a tail that stretches further out onto the right for a little while. This tail is the collective signal from the stars that are brighter than the sky (aka the sky background).
At the left of the peak there is the signal coming from the deep sky.
It is clear that if you want to “properly” expose in-camera deep-sky targets, you will have to push the exposure for the image, thus pushing the whole histogram to the right, clipping not only the stars but the entire sky. You will get a white frame, and this is why the well-known “Expose To The Right (ETTR)” technique is not useful for deep-sky astrophotography.
Now that we know what we are looking at, let’s see what we should be looking for: collect as much signal from our target as possible.
The sky brightness determines how much usable signal from your deep-sky target you can get. In how much you can collect all the available signals depends on your specific gear.
We could go very technical here, talking about SQM measurements for the sky brightness, sensor’s quantum efficiency, swamping the camera readout noise, and more.
If you are interested to know more about all this I suggest you have a look at the video below.
But for most of us shooting with a DSLR or mirrorless camera, knowing all the parameters to remove the guesswork when choosing the camera setting is virtually impossible; as for common, everyday cameras, those specs are often not disclosed.
Instead, we can rely on the following rule of thumb: set your ISO and Aperture and choose your shutter speed so that the peak of the histogram (the sky brightness) is at about ⅓ from the left edge and that there is a gap between the histogram and the left edge.
This ensures you are not clipping all the stars to pure white and that we are collecting as much as the faint signal, since the histogram is not crammed on pure black.
Remember that what we are determining here is the shortest exposure you need to collect all the available signal from the deep sky. Particularly in a dark location, this exposure can be several minutes long.
Targets such as Andromeda and the Great Orion Nebula have huge dynamic range, with very bright cores and very faint outskirts. Inevitably, to get the faintest parts of those targets, you will clip the brightest ones: you need then to shoot sequences with shorter exposures and combine all the data later on in post to create some sort of HDR.
Once you have determined the length of a single exposure, to clean up the signal what counts is the total integration time, i.e., how much total exposure time you reach by shooting for image stacking.
This can all seem like another academic exercise with no real-life use, but it does have some very practical applications.
Say you are imaging with a small tracker: taking good long exposures can be tricky. But if your sky brightness lets you collect all the usable signal from the deep sky in 30”, then that is all you need. No reason to shoot for 180” and throw away half of your images because of tracking errors.
Choosing The Proper Aperture
As per the aperture, if you are using a photographic lens with variable aperture, choose the widest setting that is usable.
Optical and chromatic aberration often improve when stepping down the diaphragm (i.e., reducing the aperture): very few photographic lenses are well corrected when used at full aperture.
Try stepping down your lens by one stop if you are not happy with its full aperture performances.
Set The ISO By Exploiting Your Camera ISO Invariance
As per the ISO, you should take advantage of ISO invariance. Most cameras are ISO invariant in a certain range. Within this range, there is no noise penalty in brightening in post underexposed images rather than increasing the ISO in camera.
You can find online where your camera is ISO invariant or determine this yourself.
Start by taking a properly exposed image at, say, ISO 3200.
Then shoot a series of images that are underexposed by 1-, 2- and 3- stops. Do this by halving the ISO after every photo (ISO 1600, ISO 800, ISO 400).
Finally, brighten the underexposed images in Photoshop by 1-, 2-, and 3-stops and compare the noise with the original image shot at ISO 3200.
If ISO 800 is in your camera ISO invariant regime, the image shot at ISO 800 and brightened in post will not show more noise than the one shot at ISO 3200.
Astrophotography Settings for Lunar And Planetary Astrophotography
Every kind of astrophotography has to deal with the seeing, i.e., the quality of the sky (haze, fog, air turbulence, humidity, …), but because you will be shooting at high magnification, seeing is much more of a problem in Lunar and planetary astrophotography.
Luckily, the Moon and the Planets are fairly bright and most of the time it is not difficult to keep a shutter speed fast enough to freeze the detrimental effects of the seeing.
For the Full Moon, a starting point is using the Looney f11 rule: set your camera to ISO 100, shutter speed 1/100, and f/11 to have a good exposure.
The Looney f11 rule is only valid for the Full Moon, when Moon brightness is at its maximum. For the other phases, you must increase the ISO or step up your lenses (wider aperture) to make up for the reduced brightness.
Ideally, you don’t want your shutter speed to drop below 1/40s to get sharp images.
If you can shoot in full HD or 4K, consider shooting videos of the Moon rather than shoot for image stacking using RAW images: you will collect data much faster.
For video, you want to set the camera for:
- the highest bitrate (i.e., the video compression, the less, the better)
- the highest resolution compatible with that bitrate
- the higher frame rate compatible with the previous settings
On my Olympus OM-D that is using the all-intra bitrate, full HD resolution, and 30 fps.
Make sure you use manual shutter when shooting video, so you can use shutter speeds faster than the frame rate.
Astrophotography Settings for Star Trails And Starry Landscapes
The easiest type of astrophotography probably is creating star trails. Don’t get me wrong: it is not trivial to create nice star trails, but the main difficulty is an artistic one rather than a technical one.
Star trails share with starry landscapes the quest of finding the proper location, an interesting foreground and getting the composition right.
In these types of photography, a great sky cannot hold the entire photo alone: it needs a great foreground.
In both types of photography, it may be best to expose the foreground and the sky separately and then merge the two together in the final image.
Expose the ground so that you can see some details: if there is no moon and you are not doing light painting, this can require a long exposure.
As a starting point to expose for the foreground, try using ISO 400 and something like f/4 or f/5.6 to use the lens at its sweet spot and compensate with longer exposures. Snap a sequence of images to stack them in post to reduce the noise and improve on the details.
For the sky we need to consider the following:
Settings for Star Trails
- ISO: try staying about 200 to 400 to avoid clipping the stars to pure white (as we saw when discussing how to choose the settings for deep sky astrophotography)
- Aperture: something like f/4 or f/5.6 is good
- Shutter Speed: set the shutter speed to 20s/30s
- Note: Shoot for as long as you can (minimum 2hr)
Settings for Starry Landscapes
- Shutter Speed (not Tracking): use the NPF or 500 rule to select the slowest shutter speed for which stars are round.
- Shutter Speed (Tracking): start with 60s and increase if you can.
- Aperture: use the widest usable aperture for your lens.
- ISO: A good starting point for ISO is 1600 or 3200, depending on your camera High ISO performances. If you are tracking, you can lower your ISO to retain a larger dynamic range.
Note: Shoot for Image Stacking and try to have a total integration time of at least 10 minutes. If the foreground is very imposing, shooting for longer may get difficult to properly align the sky with the foreground due to Earth rotation.
Shoot For Image Stacking
Image stacking is a technique that consists of shooting a bunch of images of the same target with the same settings.
You can comfortably do that using an external intervalometer. For the Moon and the planets, you can shoot video clips and stack the video frames.
The technique is central to astrophotography because it improves the signal-to-noise ratio.
While the stacking will not reveal data that is not there in the individual frames, by combining all the images, you will greatly reduce whatever random noise there is.
In doing so, even the faintest signals can now have a chance to stand well above the background noise, thus becoming more visible once you will perform the histogram stretching on the stacked image.
Conclusion
This was quite a long and at times technical article. There is much more to say, particularly if you want to be rigorous and precise, but this goes beyond the scope of this article.
Here we wanted to give you some go to settings to start with and, more importantly, the key concepts you should consider when choosing your camera settings for your astrophotography.