If you are new to astrophotography, you probably have many questions you want to ask and many doubts you would like to clarify.
I spend a good deal of time in astrophotography groups and forums and I see the same questions asked over and over.
Here I try to answer the 20 most asked astrophotography questions by beginners and to offer links to dig deeper into the different arguments.
How To Ask Your Questions And Have Useful Answers
Before jumping on the Q&A sections, let me remind you that there is nothing less helpful than asking a wide-open question.
Would you go on Facebook to ask “hey guys, I’m hungry! What should I eat?”
I guess no. So, why would you think it is ok to join an astrophotography group or forum and ask “What telescope should I buy?”
Sometimes, these questions are not well received by the more expert people, and they get quite annoyed (and will not try to hide it).
They get annoyed mainly for two reasons: 1) we may read the same exact question ten times a day and 2) formulated in this way, your question is hopeless.
But we should all be more tolerant: as a beginner, you may not know that planetary observation and photography require different setups than those for deep sky.
How should you know that?
But here is the thing: you surely know what you would like to do with a telescope and what your budget is.
When asking for something and you want to receive helpful answers, remember to say what it is that you want to do, with what you want to get, and how much your budget is.
Astrophotography Frequently Asked Questions (FAQ): Tech Topics
I Don’t Know What You Are Saying To Me: What Do All These Technical Terms Mean?
Astrophotography is perhaps the most technical kind of photography, much closer to science than arts. It should come with no surprise that the astrophotography vocabulary is rich in obscure acronyms and technical terms.
Even the most basic questions can have answers that are hard to understand.
- “What can I do to get better, round stars?”
- “You should start TRACKING using an EQ mount and possibly an OAG or other forms of GUIDING for better tracking in RA and DEC. Mind your PA and balance EAST-HEAVY. Or, STACK shorter SUBS.”
Sounds familiar, doesn’t it?
To help you get to know the astrophotography language, here is a glossary of the most common astrophotography terms and acronyms you should bookmark for further references.
What Is The Best Way To Focus On Stars?
Focusing on the stars is difficult, particularly if you keep relying on the camera autofocus. Stars are too dim for the AF to lock on them, but if you really want to use your camera AF (or you have to), it is best to focus on the Moon and then lock the focus.
Focusing in daylight on a distant object is not really a good method: you may alter the focus by accident, some lenses may reset themselves if the camera is turned off or it goes in stand by. With many zoom lenses, the focus is altered when zooming in or out.
Finally, the temperature may affect the focus, as the lens (or telescope) shrinks or expands in response to the change in temperature.
For all practical considerations, the Moon, the Stars, and the Planet are all at infinity.
The best way to accurately focus on stars is to use the live view to magnify a bright star, and manual focus while looking for three tale-telling signs.
- The better the focus, the smaller the stars on the camera LCD screen;
- The better the focus, the more faint stars are visible on the camera LCD screen;
- The better the focus, the smaller the purple fringing around bright stars.
If you want to know more, have a look at these tips and tricks for getting a perfect focus on stars.
What Is A Bahtinov Mask And Should I Use One?
A Bahtinov mask is a grid that works as a focusing device: when placed in front of a lens or a telescope, it creates three diffraction spikes around the stars.
These spikes move while focusing and when they all cross at the star, you are sure you are in perfect focus.
Bahtinov masks are affordable and very useful devices every astrophotographer should have. Just remember: the shorter the focal length, the finer the grid must be in order to create usable diffraction spikes.
Here you can learn more about the use of a Bahtinov mask and DIY alternatives.
What Are The Best Camera Settings For Astrophotography?
In everyday photography, you can rely on the exposure triangle to set your exposure right and have the desired creative effect, such as motion blur or a shallow depth of field.
But in astrophotography, your exposure depends on whether you are tracking or not the sky, and on the sky brightness.
With DSLR and mirrorless cameras, the process of determining the best settings is rather empirical, particularly if you are tracking the sky.
Here, using the widest usable aperture means to set the lens to the widest aperture for which optical aberrations are negligible, and that gives a sharp enough image.
An ISO Invariant means that the noise you get from using high ISO is the same as that you would get by brightening in post-processing an underexposed image taken at lower ISO.
Using lower ISO without introducing more noise is a great way to get the widest possible dynamic range for your sensor.
With the aperture and ISO set, it is now time to get the proper exposure time: this is limited by your mount tracking accuracy for the imaging setup you are using (long focal length and heavy equipment require better mounts) and by the sky brightness.
Take some test shots at a different length to determine what is the longest exposure your mount allows you to take, which does not show trailing stars. You can start with a 120” exposure and move from there.
Once you get that upper limit for the exposure time, take a couple more test shots making sure the peak of the histogram (which represents the sky brightness) clears the left edge of the scale and moves ⅓ to ½ toward the right edge.
If you have an astro camera and you track the sky, you can use the declared values for quantum efficiency, readout noise, etc, to calculate what is the shortest exposure time that is long enough to capture all the details the brightness of the sky allows. But this is more advanced stuff than what we want to discuss here.
If you are not tracking the sky, then the starting point is using the NPF or 500-rule and calculating the maximum exposure time for which you have reasonably round stars. Then, use the widest possible aperture to let more light in and boost the sensor signal using high ISO.
What White Balance Should I Use? And Should I Shoot In Raw Or JPEG?
White balance (WB) is important when trying to render natural colors and/or create a moody image. When shooting in JPEG, you have to properly set the WB in camera, but this is quite a challenge in astrophotography.
Luckily, JPEG images have little use in astrophotography, and if you can, you should always shoot in RAW to get the best possible data to post-process and edit.
I use daylight white balance for all my astrophotography, but as I shoot in RAW this does not really matter, as I can properly tweak the WB in post.
Not many “cosmetic” settings are applied to the RAW images: in-camera White Balance and noise reduction do not affect your RAW image, but only the preview you see on the camera LCD screen.
Just remember to disable long exposure noise reduction, to prevent the camera from taking a dark frame after every image, and any image stabilization you may have.
How Do I Find And Frame My Target?
How can one frame a small and often invisible target? Luckily, you have several options.
If your budget allows it, you could get a GoTo mount. First, perform a two or three-stars alignment to let the mount know how it is oriented. You can then input the name of your intended target, and the mount will sway the payload to frame it.
A more budget safe alternative is to use a red dot star finder mounted on your camera hot shoe. This device projects a laser on a clear screen, so that when you look through the star finder you see a red dot superposing to the sky. Sway the camera so that the dot superpose to the intended star, planet, or the general area where your target is.
Or, you can learn how to star hop from a visible star to your intended target. With a bit of practice and the right equipment, you can frame your target in minutes.
Here you can know more about how to manually frame any target.
What Is Polar Alignment And How To Do It?
Polar alignment is the process of aligning an equatorial mount to the Northern or Southern Celestial Pole (CP).
If you want to do deep-sky astrophotography, this is one of the most crucial steps in setting up your equipment, and you need to master it.
Since the stars appear to revolve around the CP, once aligned to the NCP or SCP, an equatorial mount will rotate the payload in sync with your intended target, nullifying both the target drift and rotation in the field of view of the instrument.
In the Northern Hemisphere, the NCP is a bit more than a full Moon diameter from Polaris, which is used as a “landmark” for aligning the mount via a polar scope or other electronically assisted methods.
In the Southern Hemisphere, the SCP is more difficult to locate as the reference is the faint sigma-Octans constellation.
Here is a detailed guide on how to perform a polar alignment.
What Are Calibration Frames And How Do I Take Them?
Calibration frames are images used to improve the quality of your light frames (the actual images of your target).
They do so by removing specific kinds of noise from your light frames, as well as even up uneven field illumination due to vignetting and/or dust and dirt in your setup. There are four types of calibration files.
Dark frames are used to remove thermal noise and hot pixels. With the lens cap on, shoot these frames with the same settings used for your light frames. Ideally, dark frames must be recorded at the same temperature as your light frames.
Bias frames deal with your sensor readout noise. With the lens cap on, record bias frames with the same ISO used for your light frames, but use the fastest possible shutter speed.
To compensate for uneven field illumination, you use flat frames. These are taken without changing anything in your setup (camera orientation, filters, focus, lens aperture, accessories). Frame a uniformly lit light source (the sky or a light panel) and shoot your flats taking care that the histograms for the R, G, and B channels peaks at ½ of the range.
If the exposure for your flat frames is longer than 1s, you need to take flat dark frames as well. These are taken in the same way as dark frames, only with the same settings used for collecting your flats rather than the light frames.
Our guide on calibration frames will tell you more about how to take and use these frames.
FAQs On Gear For Astrophotography
What Do I Need To Start With Astrophotography?
To start photographing the many wonders of the night sky, you do not need much: your DSLR camera and lenses are good enough to get started in astrophotography.
Don’t rush into buying specific and expensive gear.
If you do not like sleepless nights, waiting hours in subzero temperature, or being eaten alive by mosquitos in summer, astrophotography may not be your thing. Of course, nothing wrong with this, but it is better to know it before investing lots of money in specific gear.
A telephoto or zoom lens of about 200-300mm is ok for taking images of the Moon showing some details of the lunar surface. While the tripod is highly recommended, near the Full Moon you could even shoot handheld using the continuous shooting mode.
Deep sky astrophotography is, perhaps, the most demanding type of photography. You can still use your camera and lenses, but you really need at least a star tracker such as the Omegon Minitrack LX2.
A star tracker rotates the camera in sync with the stars, allowing you to take the needed long exposure without having the stars trailing in the images.
What Mount Should I Get?
The mount is the single most important piece in your astrophotography equipment: everything else should be chosen considering the type and size of the mount you have or plan to buy.
When it comes to considering the mount capabilities, astrophotography is much more demanding than visual observation, and deep-sky astrophotography is much more demanding than lunar, solar, and planetary astrophotography.
This is because with deep sky we are trying to photograph very dim targets. Thus we need reliable and accurate tracking to have pinpoint stars in our (very) long exposures.
Every mount is rated with a maximum payload, and for deep-sky astrophotography, the rule of thumb is not to load your mount with a payload of more than 50% – 60% of its maximum capacity.
This ensures the mount performs at its best, without strain or stress on the motors: you’ll get better stars on your long exposures and will improve the lifespan of your mount.
For visual observations, you should be fine as long as you do not exceed the maximum payload.
For planetary and lunar imaging, there is no need to be too conservative with the payload weight, as we usually record videos with a high frame rate: tracking does not need to be as accurate as for deep sky astrophotography.
Finally, you should decide what kind of mount you need: for visual observations and lunar and planetary imaging, you can use an alt/az mount. For deep-sky astrophotography, you need an equatorial mount.
What Is The Difference Between Alt/AZ And Equatorial Mounts And Which One Should I Get?
Both mounts will track your target, but they do so differently.
Alt/Az mounts follow the target by moving the camera left/right and up/down. This is good enough for observing with a telescope or for taking the short exposures typical of lunar and planetary imaging.
With the long exposure typical of deep-sky astrophotography, alt/az mounts fail to compensate for the field rotation, i.e., the rotation of your target in the field of view of the instrument.
For this, you need an equatorial mount.
An equatorial mount is aligned to the celestial pole through a process called polar alignment. The camera rotates in sync with your target, and both drifting and field rotation are naturally nulled.
What Is A Star Tracker? Do I Need One?
A star tracker is a lightweight, affordable equatorial mount that can be used on a normal photographic tripod.
With the exception of the SkyWatcher Az/GTi alt/az mount, which can also be adapted to work in equatorial mode, star trackers lack GoTo capabilities.
With a maximum payload capacity between 2kg (4.5lbs) and 5kg (11lbs), star trackers are the perfect choice for starting astrophotography with your current DSLR or mirrorless camera.
If you are interested in astrophotography, even if this means starry landscapes or Milky Way shots, a star tracker is the best piece of equipment you should invest in.
What Telescope Should I Get?
Ask this and you will get a billion different answers, particularly if you do not state what you want to do and how much your budget is.
More often than not, a rig for observation is not good for astrophotography, and a setup for solar system exploration and photography is not good for the deep-sky.
And this is not because we are getting picky and we want anything less than the best possible option. It is because observation and photography have different requirements, and the same is true for the different types of targets as well.
What you need for the Moon is nothing like what you need for a distant galaxy.
To help you get your first telescope, or, at least, to understand what buying a telescope means, we have put together this guide on things to look for when buying a telescope.
Can I do Astrophotography With My DSLR?
Good astrophotography with a DSLR or mirrorless camera is possible and surely is the simplest and most budget-friendly way to start.
A star tracker, a device that allows rotating the camera in sync with the stars, is the key to unlock the night sky.
With a star tracker, you will easily improve the details in the starry sky when photographing the Milky Way and night landscapes. It will also allow you to have some fun with star fields and deep-sky astrophotography, particularly with bright nebulae, the Andromeda Galaxy, and many other famous targets.
What Are The Best Cameras For Doing Astrophotography?
Without considering dedicated astro cameras, DSLR and Mirrorless cameras can be great imaging tools for astrophotography.
The camera sensor is what makes the difference: Full-frame cameras usually have sensors with pixels size larger than any cropped sensor. Larger pixels mean less noise and probably larger dynamic range.
In short, full-frame cameras give you the best signal-to-noise ratio.
But modern APS-C and micro four-thirds cameras are also perfectly capable of delivering great images. And because of the small pixels they use, they give higher optical resolution than full-frame cameras for any given lens or telescope.
When looking for a camera suitable for astrophotography, there are more things to consider other than the sensor size:
- a live view with focus assisting (focus peaking or magnification) is a must-have for precise focusing;
- the possibility to use an external intervalometer is also a must-have for deep sky astrophotography;
- High-speed HD or 4K video is extremely useful if you are into lunar and planetary astrophotography;
- Good battery life is a must for your long deep-sky astrophotography sessions;
- A weather-sealed body and lens can help when photographing in very humid or frosty conditions.
If you are really into deep space astrophotography and budget is not an issue, monochrome astro cameras with active cooling are the best things you could buy, together with a filter wheel and narrowband filters.
The absence of the Bayer matrix in monochrome cameras ensures extremely high sensitivity to light, while the sensor cooling minimizes thermal noise for cleaner images.
One-shot cameras (color) are also better than classic DSLR and mirrorless, as they do not have the IR/UV cut filter in front of their sensor and are more sensitive to the Ha signal from emission nebulae.
The main downsides of using astro cameras with respect to everyday cameras are that you need a computer to control them, and you must provide a 12V power source for the cooled ones.
What Are The Best Camera Lenses For Doing Astrophotography?
Photographic lenses are perfectly capable of delivering great images, with, perhaps, the exception of planetary astrophotography, as extremely long focal lengths are required.
A lens for astrophotography does not need autofocus, nor image stabilization: manual lenses such as the Samyang 135 f/2 are great buys.
What counts the most is aperture, and you should aim to get a lens with the widest usable aperture you can afford. With usable aperture, I mean the widest aperture that minimizes chromatic aberration, coma, and other optical aberrations, while producing a sharp image.
Usually, lenses perform best when not used wide open, particularly legacy lenses.
Before buying a lens for astrophotography, be sure you do a bit of research: this post on Lonely Speck lists many interesting lenses that are great for photographing the night sky.
Also, by searching a particular lens model on astrobin will return plenty of image samples to give you an idea of how that lens performs in real life.
What Filters Should I Use For Astrophotography?
Filters are essential to astrophotography, but you need to use the right one with the right gear and for the right target.
Mind that most filters are available only in size 1.25” and 2” (M48), while others may be available as clip-in filters for specific camera brands and models.
The most common filters can be grouped as:
- Didymium filters for light pollution reduction (LPR);
- Broad-band filters for better light pollution suppression;
- Ultra-High-Contrast, dual-band and triband filters to enhance emission nebulae with color cameras;
- Narrow Band filters for monochrome cameras;
- IR/UV cut and pass filters for planetary and lunar astrophotography;
- White light filters for solar photography;
Didymium filters, such as the Hoya Red Intensifier/Star Scape and other affordable LPR filters use rare earth elements to absorb yellow and orange light, like that emitted by High-Pressure sodium and mercury lights used in old street lights. Didymium filters do not work in light pollution from L.E.D lights.
Broad-band interference filters such as the Astronomik CLS and Optolong-LPRO are more efficient in suppressing light pollution and often give better, more balanced colors. They are suitable for general astrophotography.
UHC, Dual-Band, and Tri-Band filters such as the Baader UHC Nebula Filter or the Optolong L-enhance and L-extreme, are very aggressive and filter out most of the light in the visible spectrum. They mostly pass only HA, HB, and OII wavelengths, strongly enhancing emission nebulae and are more useful with astro cameras and modded DSLR having their IR cut filter in front of the sensor removed.
Narrow Band filters let pass only one type of light wavelength: Ha, OIII or SII. The filters must be used with monochrome cameras and allow to image emission nebulae even from the city and, to some extent, with the full Moon in the sky. The main drawbacks are they are costly and time-consuming, as each band has to be acquired separately.
IR cut filters are great for capturing lunar and planetary details, as IR light is less affected by the seeing, but you will have a black and white image and you need a modded DSLR or planetary camera. Astrophotographers usually combine IR images with RGB ones to improve the quality of the final image.
White Light filters are solar filters for safely photographing the Sun. This filter is safe to photograph and observe sunspots, surface granulation, solar eclipses, and planet transits.
WARNING: The improper use of a solar filter can have you blind or burn your equipment. Do not let children unattended when observing the Sun.
FAQs On Astrophotography Post-Processing And Editing
What Image Stacking Is And What Software Should I Use?
In astrophotography, a good noise-to-signal ratio is necessary for having images of good quality, and image stacking is the only noise reduction method that will boost the image details rather than smear them out.
When you shoot for astrophotography you should take a sequence of images, rather than a single exposure.
Since you will not change settings, focus, or framing during the sequence, the only variable between the different images is the random noise.
When stacking the images together, the random noise is faded out, while the real signal is strengthened.
There is different software for doing image stacking, depending on if you are after DSO, starry landscapes, or planetary and lunar astrophotography.
Our guide on image stacking will tell you more about image stacking and which software you should use.
What Does Stretching The Image Means And What Software Can I Use For This?
In deep sky astrophotography, image stretching, also known as histogram stretching, is the process of iteratively using levels and curves to slowly extract details from the seemingly dark background.
The histogram stretching works best on images resulting from the image stacking process.
Our guide on astrophotography stacking software will tell you more about how to perform the histogram stretching.
What Software Should I Use For Astrophotography? Can I still use Lightroom or Photoshop?
Editing in astrophotography is a big deal and involves very technical steps, leaving little space for your artistic vision.
Image stacking and image calibration are two crucial steps in the editing workflow and neither Lightroom or Photoshop are suitable for this. Instead, look at specific software such as Autostakkert!, DSS, Siril, and many more.
What is particularly nice with Photoshop is that there are many interesting and useful action packs and plugins specifically made to help post-processing astrophotography images.
Also, keep in mind that different kinds of astrophotography may require different software. Here is a comprehensive roundup of post-processing software for editing your images.
Here you have it: the answers to the 20 most commonly asked questions by beginners in astrophotography.
But many more questions await to be answered… maybe in a second article with 20 more commonly asked questions in astrophotography 🙂