Introduction to Landscape Astrophotography in So Ill: Part 1, Section 3 of 6

 Camera Settings

We will start this off with several videos that will cover some camera settings.  We will then discuss each a little bit more after the videos.  Our guidance may differ slightly from what you see in the videos, but seeing it presented in several ways should help make it clear.

The first video is the 5-minute version by Lonely Speck, a site that focuses on astrophotography.  Everything we will tell you and more can be found on that site if you are ever looking for more information.  

The next two videos comprise a longer two-part series by photographer Nick Page.  After you click play on each, you can click the YouTube icon in the player to open it in Youtube and view it larger if you'd like.

This final video is an hour-and-a-half long.  Don't think you need to watch it.  But it will cover many basics and Royce Bair does a great job of explaining some compromises that you can make to ensure you get pleasing photos even with limited equipment.

Camera Modes

Manual mode.  We discussed in the gear section that you'd need a camera with manual mode.  Cameras use light meters and all sorts of sorcery to calculate exposure times, but they don't hold up to astrophotography. They can't factor for things like star trailing, low light, etc.  Plain and simple, you'll need to use Manual mode.  It's usually denoted with an "M" on the mode dial atop most DSLR and mirrorless cameras. 

On a phone, you'll likely need to enter a Pro or Advanced mode to access manual settings.  On an iPhone, you might need a 3rd party app to access these settings.  Also, some of the post-2020 phones have a dedicated Astro mode worth trying out.  It essentially stacks in-camera for you.

RAW.  Digital images are just files of data.  RAW files retain more data than JPEGs, allowing for more flexibility when editing the images later.  Notably, for our case, it helps us bring some detail out of the shadows.  Your camera likely stores RAW files using some name other than .raw (e.g. .arw, .nef, .cr2, .dng, etc) but that's all the same for the most part.  Most modern phones also provide the option to store RAW files when shooting in manual modes.  Check your phone or camera manual to activate RAW shooting.

Aperture

Image by Sinisa Maric from Pixabay  

Wide-open.  Aperture refers to how large the opening is within your lens to let light through.  It's usually measured in f-stops.  The numbers are actually inversed, which just means that smaller f-numbers correspond to a larger opening and more light (see this). A common theme in astrophotography is that we are "starved for light" meaning that it's dark and we rarely are able to capture as much light as we want to.  So, we want to use settings that maximize our ability to gather light.  In this case, we want the largest opening (smallest f-number).  Set your camera/lens to the smallest number; it will likely be something like f/3.5, f/2, etc.

Phone users are likely stuck with a fixed aperture.  Luckily, it is usually a rather open aperture.

Advanced topic: when using advanced equipment like cameras with great light-gathering capabilities, tracking mounts, or super open lenses (f/1.8 or smaller f-numbers), there are some advantages to "stopping down" or closing the aperture a stop or so.  This has to do with distortions in the lens at the extremes.  We won't focus on that now because most folks will still be starved for light and shouldn't sacrifice light to reduce distortion. 

Shutter Speed

Long, but not too long. There are a few common recommendations out there and we will briefly discuss each.

30 seconds

The easiest option is to shoot 30" exposures.  That's often the maximum that most cameras will shoot without using bulb mode and a separate timer.  It will help you gather a lot of light and is a good way to ensure that you see the Milky Way.  The problem with 30" is that it will likely result in "star trailing".  The earth is spinning and your camera is on Earth.  That spinning makes the stars appear to move relative to the camera.  Amazingly, even 30" is long enough for those stars change from dots to lines and for the Milky Way to get blurred in your image. 

500 rule

Another common recommendation is to use the 500 rule (or 400, or 300).  For the 500 rule, you divide 500/FL where FL is your lens' focal length (measured in mm and usually marked on the lens).  So, if you're shooting a "full-frame camera" with a 20mm lens, the 500-rule says you can shoot up to 25 seconds before trails form. 

Notice I said "full-frame camera".  Most modern DSLRs and mirrorless cameras are either "full-frame" or "crop-sensor," which refers to the size of the sensor (the thing that records the image).  Crop sensor cameras modify the focal length of a lens.  For example, my Sony a6300 has an APSC sensor with a 1.5x crop factor.  That means the 20mm lens is 30mm equivalent and my 500 rule time would be 16 seconds, not 25.  To complicate things, not all cameras' crop factors are 1.5x, so you will need to research your camera's specs in this regard.  When using the 500 (or 300 or 400) rule, you'll need to know if your camera utilizes a full-frame or crop sensor, and you will need to be able to apply the crop factor for your specific camera model.  

For phones, you can usually find the focal length equivalent online.

The problem with the 500 rule is that it was developed for film and does not account for the incredible resolution that we can achieve in modern digital photography.  Following the 500 rule will result in star trailing.  Maybe that minimal star trailing is acceptable for you if it means that you can get slightly brighter images.  That's for you to decide.  A compromise is to use a more conservative calculation like 300 or 400 in place of 500, but any of these calculations are merely guidelines and don't take the sensor into account.

NPF rule

That brings us to the NPF rule.  This calculation accounts for each individual camera's sensor and its associated resolution and pixel properties.  Short version: it is the only way to calculate the maximum exposure time that will give you true spot stars (no trails) on a digital camera.  If you value crisp celestial bodies, this is the one to use.  Multiple photo apps have an NPF calculator built-in or you can use an online calculator like this one.  The declination in So. Ill. is about 2.5 degrees and you can leave the pixel tolerance set to 7 if you can't find it for your camera. 

Other considerations

If it's windy and/or you have an unstable tripod, you may want to reduce exposure time in order to limit camera shake and associated blur.  If clouds are moving through and you want to shoot during the short windows between clouds, use a shorter exposure.

Which to use?

That depends on your priority with your astrophotography and your equipment.  If you are just starting out or your camera/lens isn't great at capturing light and you want to make sure you can see the Milky Way, then start with 30-second exposures.  As you practice and look at images on your computer, you can decide if you want to shorten your exposure time.  If you want crisp details from the stars you do capture while avoiding blur/trailing, then use the NPF rule.  We, the instructors, usually use the 300 rule or the NPF rule. 

For comparison, here are two images of the same scene.  The top image was taken at 15" and the lower image at 30".  The left pane shows the full image and the right pane shows it zoomed to 300%.  These were shot on a 24mm equivalent lens.  Using the 500 rule called for 21 seconds, the NPF rule called for 14.5 seconds.  At first glance, they look similar (ignoring the clouds that moved in) but you can see the difference in how crisp the stars and other Milky Way details look when you zoom further.

15 seconds (c) John O'Connell

30 seconds, (c) John O'Connell

ISO

ISO is... well... it's hard to explain and almost every time I see it explained, I see someone else saying they are wrong.  I don't truly understand how it works, but I know which ISO setting works well for me on my camera after performing tests.  We could get really technical about it but let's just say that the really simplified explanation is that it is a way that the sensor/processor of your camera can amplify the brightness of the image.  Higher ISOs lead to brighter images.

So let's just crank the ISO all the way up, right?!  Well, not really.  Again, an oversimplified explanation, but we often get more noise (speckles or "grain") in images when we use high ISOs.  Increasing the ISO past a certain point, which is camera-dependent (see advanced topic below if curious), has no apparent effect on your light-gathering ability.  Higher ISOs also increase the likelihood that brighter parts of your image will be overexposed, especially if moderate light pollution is present, since it is so much brighter than the MW.  You can see an example here.  So, there are good reasons to moderate our use of higher ISOs.

To keep it simple for the workshop, let's all start with a moderate ISO setting of 3200 or 6400.  That's usually a good starting point that will help us see the Milky Way.  If you want to dive deeper into this, then...

Advanced topic: Start here.  Also, you can research ISO performance for your camera from DXO Mark or various other tests people have performed and posted online.  There's also a concept of ISO-invariance where the final product of images from some cameras have the same amount of noise regardless of ISO used.  Some cameras have two base ISO levels.  For example, my Sony a7iii essentially performs just as well at 640 as it does at 100 (and better than 500!).  Some search terms to research this further would include your camera model and "ISO invariance", "dual gain", "read noise", "noise floor", or "sigma noise".  One reason to research your camera is that higher ISOs can negatively impact color range and dynamic range of your images.  If you can find a lower ISO that performs just as well, you can improve color and dynamic range.  For this reason, I often shoot at 640.  The upsides: more dynamic range, better color, and protecting highlights.  the downside: my images in the field are dark and it's hard to tell what you're getting until you brighten them in post-processing on a computer.

Focus

Manual focus, at least for the sky exposures.  Despite great improvements in autofocus in recent years, autofocus systems struggle to focus on the stars.  To ensure the best focus, we want to use manual focus.  Focusing in the dark can be intimidating at first, especially when you learn that the infinity focus point marked on the lens isn't necessarily the true infinity focus-point, but several great approaches make it very achievable. Here are 2 videos to walk you through one of the parts of astrophotography that give people the most trouble.



This video does a great job of explaining several approaches, but I would just focus on the first 2 on his list of 6 for now.

I have one variation on his first technique.  Instead of taping the lens in place, you can use a silver Sharpie to mark a line on the lens barrel and a line on the focusing ring that line up.  Then, just align the two tick marks and you'll be focused.  I (John) love this method because it allows me to shift focus for foreground shots and saves me from going into Live View every time I want to focus on stars.  Note that this won't work if your lens has fly-by-wire focusing (turning the barrel sends a signal to the lens to shift focus) instead of mechanical focusing (turning the barrel directly and physically shifts the focus).

But, on the topic of the focusing ring, be very careful to not twist that ring while you're shooting. It really stinks to get home and find out that you bumped the lens slightly out of focus.  This is a reason that taping the focusing ring can be wise, especially if you'll have any accessories on the lens, like a lens warmer.

Of course, you could break the rules and intentionally not focus on the stars.  The stars will form glowing "bokeh" balls and will often show more color.

I focused on the chairs instead of the stars (c) John O'Connell 2021

White Balance

White balance affects the "temperature" of your image.  Cooler white balance settings make the image more blue and warmer settings more yellow.  Auto white balance can help make the determination for you during the daytime but presents two issues at night: 1) it might struggle and 2) it might change throughout your shoot.  You want your images to be consistent so that you can compare them later. If you are shooting in RAW, then you can easily adjust the white balance later in editing software, so don't worry too much about getting it set perfectly. Just consistently. 

We would recommend a white balance in the 3500-5000K range for Southern Illinois depending on your personal taste.  Grant tends to shoot and edit at warmer (higher) white balance than I do and you can see that differences in our images.  The lower end will be bluer and the higher end warmer.  If your camera doesn't have the ability to set a number, try Tungsten or Incandescent. Remember, you can change it during editing as long as you are shooting RAW, so just pick something you like and run with it.

3500K, (c) John O'Connell

4000K, (c) John O'Connell

4500K, (c) John O'Connell

5000K, (c) John O'Connell

Advanced topic: You can see how the different temperatures impact night images when factoring for light pollution here.

Other Settings

Stabilization OFF - This may be called IBIS, VR, OSS, or several other names depending on the manufacturer.  The lens or camera makes tiny adjustments to help account for camera shake when you are shooting handheld. The problem is that if you leave it on while the camera is motionless on the tripod, then it still makes those tiny adjustments, causing blurry images.  You almost never want to use stabilization while shooting from a tripod, even in the daytime.

Long-exposure noise reduction OFF - This seems counterintuitive because we are taking long exposures and have concerns about noise.  The issues here are time and effectiveness.  To do LENR, the camera takes a second image of darkness and subtracts it from the first.  That means that every 30-second exposure takes 1 minute to execute.  Also, LENR doesn't always work well and may even make images worse on some cameras. 

Advanced topic: A better approach than LENR is to take a number of "dark" frames near the end of your session using all of the same settings as your sky shots, but with the lens cap on and no bright lights near it.  You can then use these to remove noise using software later.  We will discuss this briefly later in the "Execution" post.

Mirror-up mode - DSLRs only (mirrorless cameras are, well, mirrorless).  When a DSLR starts taking the image, a mirror moves.  That movement can impart a little bit of camera shake and thus blur in the image.

Screen brightness decreased - This will help with your night vision and also will help you get a more realistic view of what the image looks like.  Those screens are made for daylight viewing and images will appear way brighter than they actually are if you leave the screen turned all the way up.  Turning it down can also help preserve precious battery power.

Self-timer, timelapse mode, or a remote release - if you are not using a remote shutter release, then activate the 5-second timer or a timelapse mode so that the action of you pushing the shutter button does not impart camera shake while the camera is taking the image. 

Cover the viewfinder - another DSLR-only step.  The viewfinder on DSLR cameras has direct access to the area where the sensor is.  If light enters the viewfinder, it can bounce around and impact your image.  It's mostly only a concern for bright lights, but better safe than sorry.  To reduce the chance of a light leak, put a small piece of tape, cardboard, or purpose-built cover over the viewfinder while exposing your images.

Continue to Section 4 of 6