Astrophotography 101 - Camera Settings

This article is aimed at beginner DSLR users but should apply to other setups.

A camera's basic function is to turn photons of light into an image. They do a fine job of this during the daytime when the sun is shining but once you start shooting the milky way or DSO's at night you'll be pushing your camera to the absolute limits which will require some specialized settings.

The quick and dirty rundown

· Camera mode

o Set your camera to Manual control mode, you will need it to change these settings

· Shutter Speed (aka exposure length)

o Use the longest you can without getting star trails

· ISO (aka Gain)

o Use ISO to achieve a properly exposed image in single shots

o Anywhere between ISO 800 and 6400 is generally a good place to start

o ISO is related to read noise and dynamic range, see "In Depth" for more

o Don’t overexpose, you can't recover blown out pixels

· Aperture

o Wide open (lowest f/number) unless you notice optical issues

· White Balance

o Use daylight for natural colors

· Focus

o Use live view to manually focus on a bright star and try to make it appear as small/sharp as possible (focus peaking will help!).

· Image Format

o Shoot RAW to preserve detail, other formats will compress your image, this is especially important when stacking

· DSLR specific

o Turn image stabilization off (some smartphones have this too)

o Turn Long Exposure Noise Reduction (LENR) off if you’re taking separate dark frames

In depth

Shutter Speed (aka exposure length)

This is the length of time measured in seconds that the camera sensor is exposed to the light source. In Astrophotography you will want a very slow shutter speed to let light essentially “build up” on the sensor.

When doing Astro on a standard tripod with no tracking ability your exposure length will be limited by the rotation of the earth causing stars to blur as they move across the sky, the length before stars begin to trail is determined by the focal length and crop factor of your camera. The best way to determine what shutter speed to shoot with is by experimentation, you’re aiming for the slowest shutter speed you can use without getting star trails, you can take a test image and zoom in to check if your stars are trailing and adjust from there.

For tripod use: A good starting point for a wide lens (18mm) is about 10 seconds, as your focal length increases your exposure time will have to decrease, this is where equatorial tracking mounts come into play allowing for long exposures at high focal lengths.

Stars in a 10s exposure at 18mm

Stars trailing in a 20s exposure at 18mm

ISO (aka Gain)

ISO is essentially how much what little light the sensor detects is amplified or brightened. Recommending a ISO to shoot at for the best possible results with your setup is rather difficult because it's very camera and even light pollution dependent, when you're starting out it's usually a good idea to shoot at a high ISO anywhere between 800 and 6400 so you can see your target in your previews.

Contrary to your experience in daylight photography, lower ISO does not mean less noise.

As a general rule:

As ISO increases read noise decreases (exceptions occur if your sensor becomes invariant).

As ISO decreases dynamic range increases (meaning better contrast).

Once you get more into Astro the unity ISO of your camera is what you would ideally shoot at to maximize sensor performance if you are shooting exposures longer than 1m, otherwise, you will likely want to shoot higher than the unity ISO of your camera. (e.g. my camera has a Unity ISO of 200 and I shoot 1m long exposures so I would shoot slightly higher at ISO 400 or 800. If I were shooting 2m exposures or longer I would drop it to the Unity ISO.)

For single images: ISO is what you will use to ensure your image is properly exposed. If your image looks too dark raise your ISO and vice versa if your image is overexposed.

For stacking: ISO becomes slightly less important since you will be stretching (brightening) your image anyways in post but it will still affect your noise levels and dynamic range.

If you would like to learn more about the reasoning behind what I've said this is a great article that goes very in depth on the subject: https://darkskies.space/iso-myth/

Aperture (f-stop)

Your aperture (f/number, aka focal ratio) is how large the opening in your lens is relative to your focal length.

Generally you want to keep your lens open wide (lowest f/number, e.g. f/1.8) to let in as much light as possible unless you notice issues with your lens such as coma, chromatic aberration and/or distortion. Stopping your lens down slightly can help with some aberrations. This doesn't apply to telescopes as they have a fixed aperture.

White Balance

White Balance defines how warm or cool you image is, in landscape astro WB is typically used to a more artistic flavor than in deep sky imaging where having accurate colors is generally favored.

For single images: Using daylight WB usually yields the most natural colors.

WB can be changed in post if you shoot RAW format.

For stacking: Stacking programs usually ignore WB and even offer options for color calibration (Such as RGB background calibration in DSS) so don't worry if you chose the wrong white balance, it likely won't matter anyways.

Focus

Focus is key to insuring your image is sharp and since AF doesn’t work well at night you will have to do this by hand using MF. Start by pointing your camera at a bright star, then using live view focus to infinity, once you can see stars use focus peaking (if your camera supports it) to fine tune your focus until your stars appear as small as possible.

Astrophotography Tool has a lens control feature that's useful for fine tuning your focus beyond hand precision.

Image Format

Shoot RAW! Other formats will compress your image and therefore preserve less detail.

This will require an editing program of some kind but will allow your camera to keep all the detail the sensor captured.

DSLR specific

Turn image stabilization off.

IS is great for handheld shots but when on a tripod it can make false corrections blurring your image.

Turn Long Exposure Noise Reduction (LENR) off if you’re taking separate dark frames. Generally speaking, LENR works by applying a dark frame to each image in camera right after it’s taken so if you’re shooting a 30 second exposure you’re going to have to wait another 30 seconds for the camera to take that frame which effectively halves the active time of your camera which becomes vital when shooting deep sky objects.

Closing note

These settings are meant as suggestions and can vary wildly from camera to camera, they are a good starting point but you should experiment on your own and find what works best for your setup!