Category Archives: For beginners

Lunar imaging

Peering at the Moon through a telescope or a pair of binoculars is an incredible experience. I will never forget the first time I pointed my scope at our natural satellite: as I approached the eyepiece with my eye, I became speechless, and my jaws slowly dropped…it was love at first sight!

I soon became addicted as I went on for months observing the Moon, tracking its craters, valleys, maria, and all of its beautiful features. Until one day that wasn’t enough anymore: I wanted some cool pictures to show to my friends and family, and that’s when my astrophotography journey began.

Read my article about the Moon by following this link: The Moon.

For many like me, in fact, Lunar imaging was the first dive into astrophotography. This is because it is quite straightforward, it requires simple gear, and can be done literally from everywhere, including heavily light-polluted cities. There are a few things that you need to know about the Moon, however.

First, from Earth we only see one side of the Moon. This is due to the fact that the time the Moon takes to complete a spin on its axis equals the time to complete an orbit around Earth, which always leaves the same side of the Moon facing us. This phenomena is called “tidal locking“ and it’s more common than you’d think in the universe.

Another important aspect to consider is that our satellite is observed in phases: depending on where it is positioned compared to the Sun and Earth, we see a different portion of its surface lit.

While pictures of a Full Moon are quite suggestive, the best time to image the Moon is actually when around half or less of the disc is lit. This is because the contrast increases, and more details and features are revealed.

Now let’s see in detail the technique I use to image the Moon, using only free software. For clarity, I divided the process in three phases.

Phase 1 – Capturing

In astrophotography this is the most crucial step of the process, for obvious reasons: there’s little you can do in post-processing to fix a dull image, so focus is paramount and must be spot on.

Take all the time you need to reach perfect focus, or anywhere near that anyway, and your efforts will be rewarded. Using a Bahtinov mask (focus mask) on a bright star is usually the more efficient way to do that.

The second vital aspect is “seeing” – the effect of fast-changing, turbulent airflows in Earth’s atmosphere that can make an image look blurred or distorted. Sadly, there isn’t much you can do about this apart from sitting tight with you finger ready to hit the record button as soon as the live-view image on your screen gets clear.

Imaging the Moon in infrared (IR) using an IR-pass filter and a mono camera helps you reduce the effects of bad seeing. Also, recording more than one video obviously increases your chances to get a good image out of your session, after all it’s called “lucky imaging” for a reason.

For planetary and lunar/solar photography the most widely used software is SharpCap or FireCapture. Both are free, work great and have pretty much the same functionalities. Personally, I started with SharpCap and never changed thereafter.

I record my videos in *SER format, which is more complete and easier to work on than *AVI or other formats. I typically keep gain and exposure low (but not too low) to avoid “burning” the image. Remember: you can increase exposure and brightness in post-processing, but you can’t fix an overexposed image!

Depending on the atmospheric conditions and camera performance, I generally capture various videos of several minutes each, to get somewhere between 10,000 and 20,000 frames. This should guarantee good results.

Note: Whether or not you can fit the Moon in your field of view depends on your gear. Using a telescope with a long focal length or a camera with a small resolution (or both), you may get only a portion of the Moon in your field of view. Don’t worry though: luckily there’s a way to get around this, thanks to a free Microsoft software called ICE (Image Composite Editor). All you have to do is capture some more videos, one for each area of the Moon and continue as usual (more on this below).

Phase 2 – Stacking

Once done with the capturing phase, I load the videos one by one into AutoStakkert!3, a free stacking software that analyses the video’s individual frames, giving as a result a diagram with the overall quality of the video.

Based on this graph, I choose the percentage of total frames that I want to stack (usually somewhere between 5% and 20%). The software then chooses the single best frame (the reference frame) to which all other frames are aligned a stacked upon.

When the job of AutoStakkert!3 is over, the result is a single final image made of the video’s best frames. Generally, these images look a little blurred and certainly nowhere near the amazing picture you were expecting; nothing to worry about, this is where post-processing works its magic.

Note: If you weren’t able to fit the Moon in your field of view and you had to take several panels, all you need to do now is repeat this process for each video you took. You’ll be then left with several stacked images that you can load into ICE, which will stitch them together for you using its advanced AI and will give you a final image made of all the individual panels. Look at the photo gallery below to get a sense of the process.

Phase 3 – Post-processing

When it comes to Lunar imaging, I do most of the post-processing in GIMP, a free software that looks a lot like PhotoShop, but first I use Registax and its wavelets functionality to sharpen the freshly-stacked image and bring out as many details as possible. Watch out this step though, it is very easy to get carried away and oversharp an image!

Once done, I load the sharpened image in GIMP and crop it to leave out any stacking artefacts and to position the Moon exactly at the centre of the image. Then I adjust the exposure and add some contrast before I play gently with shadows, mid-tones, and highlights to bring out some more subtle features.

If you used a colour camera, you may also want to balance and align the RGB. I usually adjust the colour curves to get a grey-metal surface.

Now your image of the Moon is finally ready to be shared on social media with friends and family!

I hope this guide will get you started into lunar imaging as a first step into astrophotography. Bear in mind that there are many other techniques out there, my advice is to try over and over, being creative and experimenting with settings and software until you find your own method.

To download the software mentioned in this guide, go to the “Downloads” section on this blog and follow the links.


Lunar Gallery


A deeper look into Solar Imaging

Since I began my journey into astronomy and astrophotography, I’ve always been fascinated by the idea of photographing the Sun. Yes, galaxies or nebulas are perhaps more intriguing objects with their incredible shapes and dramatic colours but think about the Sun for what it represents.

Our beautiful host star, that governs the Solar System and provides life to our planet, that seems so far away above our heads and yet is so close that we can feel its warmth. Besides, what better opportunity to learn about stars than studying one so close to us?

Below is a graphic from NASA displaying the Sun’s structure and layers:

The internal structure is not relevant for photographing purposes, but it is worth mentioning that this is where the thermonuclear fusion happens (in the core precisely) and hydrogen is turned into helium. The energy produced in the process is than released in the form of visible light (yes, lonely photons!).

The atmosphere, on the other hand, is where fun stuff happens; stuff that we can actually see, if we have the right equipment of course. As we will see, different layers emit light in different wavelengths, and each can be observed with a dedicated filter.

Choosing the right one that matches your needs (and your telescope) is therefore very important and requires some research. For instance, if you get one of those cheap yellow filters, similar to those for observing eclipses, all you’ll see is a red-yellowish disc with sunspots as black dots and virtually no details.

A high-quality filter, on the other hand, not only will ensure safety to you and your instruments but will also provide sharper images through the eyepiece or camera.

These are some of the most common filters in amateur solar imaging:

  • White light (WL): A white light filter shows the Sun’s photosphere, where sunspots are best observed, at a reasonable price. If you own a refractor telescope, the best option is a Herschel wedge or prism, which is placed at the bottom of the telescope, replacing the standard diagonal.
    For other types of optics there are white light filters, such as the Baader Astrozap or Thousand Oaks’ Solarlite film, which can be mounted in front of the telescope.
  • Calcium K line (CaK): With these filters we enter a pricier category, but the costs are fully justified by enchanting views of sunspots and granularity on the lower chromosphere, in the violet part of the spectrum.
    CaK filters work best through dedicated modules placed between the (refractor) telescope and the eyepiece or camera. For different telescope designs you can get a CaK filter that can be screwed directly into the eyepiece or camera and can be used in combination with a Herschel wedge (WL).
  • Hydrogen-alpha (H-a): These very expensive filters reveal stunning, sharp features of the Sun’s upper chromosphere with flares and filaments in spectacular detail (see the gallery at the bottom of this article).
    The best way to observe or photograph the Sun in H-alpha is through a dedicated H-a telescope, such as Lunt or Coronado, although these generally come with an extremely big price tag. A valid alternative is provided by H-a filters, such as the Daystar Quark, which are screwed in the diagonal just before the eyepiece or camera. This solution, however, works only with refractors and provides better images at long focal lengths (> F/10).

As an avid solar photographer, I own several tools to photograph the Sun in nearly all wavelengths though I find myself using mostly the H-a filter, which I believe delivers the most dramatic images.

Solar photography, particularly in H-a, works best with monochrome cameras as they are more sensitive to light compared to colour cameras. Generally speaking, for solar imaging you want a monochrome camera with a CMOS sensor (with high dynamic range) and a high frame rate capability.

This is because, like the Moon and planets, the Sun is photographed through a technique called “lucky imaging”. Some of the most popular cameras for solar photography are the ZWO ASI174MM and ASI290MM.

Now let’s see in detail the technique I use to image the Sun. For clarity, I divided the process in three phases.

Phase 1 – Capturing

In astrophotography this is the most crucial step of the process, for obvious reasons: there’s little you can do in post-processing to fix a dull image, so focus is paramount and must be spot on. Take all the time you need to reach perfect focus, or anywhere near that anyway, and your efforts will be rewarded.

The second vital aspect is “seeing” – the effect of fast-changing, turbulent airflows in Earth’s atmosphere that can make an image look blurred or distorted. Sadly, there isn’t much you can do about this apart from sitting tight with you finger ready to hit the record button as soon as the live-view image on your screen gets clear.

Imaging the Sun in the early hours of the morning (9-12am), when the Sun is high enough, helps mitigating the effects of seeing whereas places surrounded by water tend to have less turbulence in the low layers of the atmosphere.

Also, recording more than one video obviously increases your chances to get a good image out of your session, after all it’s called “lucky imaging” for a reason.

For planetary and lunar/solar photography the most widely used software is SharpCap or FireCapture. Both are free, work great and have pretty much the same functionalities. Personally, I started with SharpCap and never changed thereafter.

I record my videos in *SER format, which is more complete and easier to work on compared to *AVI or other formats. I adjust gain and exposure to be anywhere between 70-90% of the histogram, depending on seeing conditions. Over this range, the image is overexposed and will appear as a bright patch with no details.

Bear in mind that the higher the exposure time is, the lower the frame per second (FPS) gets, meaning you’ll need longer videos during which the seeing could turn bad or clouds may roll in (a classic!). On the other hand, higher gain means more noise, so it’s important to find a good balance between exposure time and gain.

For solar photography, capturing around 2000-3000 frames is generally enough, as you only need between 300-500 good frames for a quality image. In bad seeing conditions I go as far as 5000 frames per video, hoping that at least 5-10% turn out to be good.

It is also recommended to take flat frames to remove signs of dust from the optics or camera sensor and to minimise any vignetting effect.

Phase 2 – Stacking

Once I have my set of videos, I load them one by one in the stacking software AutoStakkert!3 (also free), which analyses them by evaluating each single frame and giving as a result a diagram with the overall quality.

It’s based on this graph that I choose the percentage of total frames that I want to stack (usually between 10% and 20%). The software then chooses the single best frame, the reference frame, to which all other frames are aligned. If you took any flats, this is the right moment to use them.

When the job of AutoStakkert!3 is over, the result is a single final image made of the 10-20% best frames of the video. The stacked image generally looks a little blurred and certainly nowhere near the amazing picture you were expecting; nothing to worry about, this is where post-processing works its magic.

Phase 3 – Post-processing

The first thing a stacked image needs is some sharpening to bring out as many details as possible. This step can be done in any image-processing software although (free) astronomy tools such as ImPPG or Registax do an exceptional job, in my view.

While for planetary and lunar photography I usually work with Registax, for solar imaging I prefer the functionalities in ImPPG, which uses Lucy Richard deconvolution technique.

Here I adjust the Sigma and Amount parameters to sharpen the image and based on the histogram, I carefully move the Tone curve to bring out prominences while also trying to keep surface detail.

Once I’m done with ImPPG, I do the final adjustments in GIMP, a free software that looks a lot like PhotoShop. The first thing I do is crop the image to leave out any stacking artefacts, then I adjust exposure and contrast and play slightly with shadows, mid-tones, and highlights to bring out some more subtle details.

Now, this final step may come as a surprise to you, but I can assure it is common practice. As monochrome cameras represent the best option for solar imaging, the final image is of course black and white and as such it must be coloured artificially.

To do that I convert the image from grayscale to RGB, and with the use of curves in the red, green, and blue channels I give my solar image the colour I like. As we saw before, Calcium operates in the violet part of the spectrum so I would give the Sun taken with a CaK filter a bluish, violet tint.

Hydrogen-alpha, on the other hand, operates in the red-orange part of the spectrum so my H-a pictures generally have a reddish, gold or orange hue, depending on my mood.

To achieve that I push up the curve in the red channel and move down the curves in the blue and green channels. I know, I know…it sounds like cheating, but this is solar photography!

I hope this guide will get you started into solar imaging. Bear in mind that there are many other techniques out there, my advice is to try over and over, being creative and experimenting with settings and software until you find your own method.

The Sun is a dynamic, ever-changing target that never ceases to amaze; whether in a maximum or minimum solar cycle, there is always something going on with our star!

Remember: NEVER EVER point your telescope toward the Sun without using a proper, safe solar filter. Looking directly at the Sun can and will damage your eyes and your instruments irreversibly! Also, always ensure that the solar filter is well attached and stable before pointing your telescope toward the Sun.


Solar Gallery


A complete guide to buying the first telescope

Check out any online telescope store and the first thing you’ll notice is that there’s such a vast, bewildering choice that picking the right one may prove somewhat problematic.

Purchasing a telescope is an investment and as such it requires proper research. This beginner guide will help you analyse all the vital aspects to consider when buying the first telescope. I hope it will help you make the right choice!

A personal choice

“What is the best telescope to buy?” I’ve read this question many times on astronomy or astrophotography forums and the answer to that is very simple. As astronomers like to say: “The best scope is the one you’ll actually use!”

While this may sound like an annoying answer at first, in reality it says it all. I’ve seen many people starting with a lot of enthusiasm only to end up locking their telescope in a basement to gather dust. So, before rushing into a store, it is good practice asking yourself these simple questions:

  • What will I use my telescope for? Visual astronomy and astrophotography are two distinct hobbies, each with their own requirements. For instance, in visual astronomy the mount is not a crucial aspect, but the telescope’s aperture makes all the difference in the world. For astrophotography instead, a good, steady mount is essential and it’s where most of the money should be invested. Thus, before buying a telescope, make up your mind about your goal.
  • What kind of astrophotography am I in? If you decide to take on the astrophotography journey, this is the next question you need to ask yourself. Planetary imaging and DSOs astrophotography have, again, different requirements: for planetary you would have to get the largest scope you can afford and a high frame rate camera whereas for deep sky astrophotography you would need a cooled camera and filters, and the best mount you can afford.
  • Where will I use my telescope? Another important aspect to take in consideration is the weight of your gear. If you need to load your car and drive in the middle of nowhere with your telescope, you’ll find that moving a small scope is way easier and much more sustainable in the long run. If you’re lucky enough to have your own backyard or a terrace, perhaps you may opt for a larger telescope on a beast mount.
  • What’s my budget? This is an obvious one but after you answered these first question you need to decide how much you want to invest before hitting the store. This can be an expensive hobby, and it’s very easy to get carried away so determining the budget in advance will help you get the best combination of mount, telescope and accessories, without breaking the bank!
  • Where to buy a telescope? Today’s telescopes are a mix of fine, delicate optics and high-tech electronics so where you buy your telescope is as important as the telescope itself. Buying from a professional store will provide you with the best service and invaluable advice from experts in the field whereas getting a telescope off Amazon, for instance, may be cheaper but offers no service at all.

What you need to know

To choose the right telescope for your needs, it’s best to familiarise with some of the technical terms you will encounter and that may sound complicated at first; here are the most important ones.

Aperture. Often considered the most important characteristic of a telescope, this is the first notion to assimilate. A telescope’s aperture is the diameter of its main optics (lenses or mirrors) expressed in millimetres or, for larger apertures, in inches.

The aperture determines the telescope’s light-gathering ability (how bright a target appears) and its resolving power (how sharp the target appears); in general terms, larger apertures show fainter objects and finer detail compared to smaller ones.

Take it easy though and try not to catch the “aperture fever”! The larger the aperture is, the bigger and heavier (and pricier) the telescope gets. Also, if you consider that the human eye has an average aperture of 7mm, even the smallest telescope represents a huge improvement. Apertures commonly recommended for beginner telescopes range anywhere from 60mm to 12” (300mm).

Focal Length. Another crucial feature in a telescope is the focal length, which measures the distance in millimetres from the main optic to the point where the image is formed (right into the eyepiece or camera).

It’s the focal length that determines the scope’s field of view: shorter focal lengths will give a wider field of view (FoV) whereas longer focal lengths provide narrower FoVs.

As a rule of thumb, longer focal lengths are better suited for planetary imaging and astrophotography of small, faint objects such as galaxies and star clusters while short focal lengths are useful to image large targets, such as nebulas or large galaxies.

It is also important to remark that the focal length doesn’t necessarily equal the length of the telescope: certain types of telescopes, such as the Schmidt-Cassegrain (see below) use clever optical layouts to squeeze long focal lengths into small optical tubes.

Focal ratio. A key aspect for astrophotography, this is a quantitative measure of the optics’ “speed”. Written as “f/” followed by a number, the focal ratio is calculated by dividing the scope’s focal length by its aperture. For example, a scope with a focal length of 2000mm and an aperture of 200mm will have a focal ratio F/10 (2000/200=10).

Therefore, all other factors being equal, a scope with a lower focal ratio will produce brighter images than a scope with a larger one but will have a narrower field of view. In astrophotography this is quite important as it means that slow optics (> F/7) need longer exposures to collect the same amount of light as faster optics.

Magnification. This notion is quite straightforward and, as the name suggests, a telescope’s magnification is its ability to enlarge the object observed. This information is mainly useful for visual astronomy, as it helps decide the best eyepiece to use, and it’s obtained by dividing the telescope’s focal length by the eyepiece’s focal length.

For example, a telescope with a focal length of 2000mm paired with an eyepiece of 8mm will deliver a magnification of 250x. (2000/8=250).

As a rule of thumb, a telescope’s maximum useful magnification is 50 times its aperture in inches or twice its aperture in millimetres,. Note that this is already an optimistic estimate, as external factors such as atmospheric conditions will likely reduce this number.

When magnification is too high, the view will be too blurred to resolve any detail so stay away from telescopes that advertise unlikely magnifications such as 500x or more.

The different types of telescopes

Now that you have made up your mind on what your goal is, and you are familiar with the main aspects of a telescope, let’s see what our options are. Amateur telescopes can be divided into three main classes (refractors, reflectors, and catadioptrics), each with their own pros and cons.

Refractors. Ask any kid to draw a telescope and they will draw a refractor: a long tube with a lens at the front and the eyepiece (or camera) at the back. Refractors were the first type of optical telescope ever designed and their popularity has remained intact for centuries.

Refracting telescopes deliver the finest, sharpest images per aperture (a consequence of the fact that they use lenses rather than mirrors) and are best suited for wide field astrophotography.

Generally featuring small apertures (up to 150mm) and short focal length, these telescopes can capture vast areas of the night sky to include large objects.

On the other hand, however, the typically short focal lengths means that refractors are not ideal to image galaxies, globular clusters, or planets. Photography of the Moon and the Sun is still possible, although with less details compared to larger-aperture telescopes.

Refractors usually represent a good choice for beginners as they require virtually no maintenance, and their wide field of view is somewhat more forgiving than larger telescopes when it comes to mounts’ tracking imperfections. Besides, these are the most compact, lightweight telescopes, which are perfect for astronomy on the go.

If this type of telescope suits your needs, make sure you opt for an apochromatic (APO) refractor. These are telescopes that use lenses made with extra-low dispersion (ED) glasses and other materials to reduce the false colour typical of achromatic refractors.

Although more expensive than achromatic refractors, the price of APOs has decreased over the years becoming way more affordable.

On the downside, the cost of refractors with apertures over 115mm is prohibitive and their weight and balance quite unmanageable, especially for beginners. Also, these telescopes often require a field flattener to counteract the field curvature of the optical system and improve edge sharpness.

Reflectors. As astronomers usually say, “aperture is king”. This is to say that telescopes with larger apertures gather more light and thus show more details, making aperture one of the most regarded feature when buying a telescope. Well, reflector telescopes offer the larger aperture for the money!

Compared to refractors, in fact, reflectors (or Newtonians) don’t have a lens at the front but use a specially curved primary mirror at the bottom end of the telescope to gather light.

From here, the light is reflected and pointed to a diagonal secondary mirror, which then directs it to the side of the tube, where they are met by an appropriately placed eyepiece or camera.

As mirrors are generally cheaper than lenses, this design allows for much larger apertures than are possible with refractors, at a fraction of the price.

Reflectors, however, require continuous adjustments to ensure that the internal mirrors be perfectly aligned; this practice is called “collimation” and is often regarded as the main disadvantage of such optics.

At mid-size aperture, reflectors usually work best with focal ratios between f/4 and f/8, useful for wide field astrophotography. With large apertures, instead, reflectors are generally optimized for visual observations of faint, deep-sky objects such as nebulae and galaxies, but require much sturdier mounts for astrophotography.

Catadioptrics. The third class of telescopes was invented out of the desire to mix the best characteristics of refractors and reflectors: as a result, these telescopes, called catadioptrics, use a combination of lenses and mirrors and have very specific designs.

There are several types of Catadioptric telescopes but the most common among amateur astronomers are undoubtedly Schmidt-Cassegrain and Maksutov-Cassegrain.

These telescopes have a lens at the front, called corrector plate, and a curved mirror at the back; similar to a refractor, the eyepiece is placed at the back.

The main characteristic of such telescopes, and the most evident, is their very short and compact design, which makes them more portable than reflectors or refractors when it comes to large apertures.

Catadioptric telescopes usually come with very long focal lengths and slow focal ratios (> F/10), thus working great on small targets such as planets or galaxies and star clusters.

Besides, most models also allow for the addition of focal reducers to shorten the focal length turning the telescope in a sort of all rounder.

Catadioptric telescopes provide sharp images but have a few drawbacks. First, like Newtonians, they need to be always perfectly collimated to ensure that the lenses and mirrors be properly aligned.

Also, due to their short, compact design, these telescopes are particularly subject to dew formation on the corrector plate, thus needing extension tubes and electric dew heaters, which add up to the cost.

Finally, catadioptric scopes take longer than other telescopes to cool down to the temperature of the night, which is vital for producing high-quality images. This means that these telescopes must be left outside for hours before you can actually start using them.

The different types of mounts

Once you know you have decided which telescope you want to get, it’s time to focus on the most critical aspect: the mount. If you are interested in DSOs astrophotography, here’s where you have to invest most of your money: any telescope, even the best one, is not worth much without a stable, precise mount.

Some telescopes, especially those for beginners, are sold with a mount and tripod as a package and could represent a quick, easy choice. This solution can be convenient for visual astronomy or for planetary astrophotography.

However, if your goal is DSOs astrophotography, I’d recommend to ditch this option and choose a proper equatorial mount straight away, which will save you quite some money as you won’t outgrow it too soon. As a saying goes: buy cheap, buy twice!

Quick note: in this guide, I will only refer to computerised mounts (“GoTo” mounts) rather than manual ones, it is the 21st century after all! These mounts have a built-it computer with a database of celestial objects and their coordinates, so after a first star alignment, the mount can slew to virtually any object in the sky and track them as they appear to “move”.

There are two broad categories of mounts (with some variants), let’s explore them.

Alt-azimuth mount. As the name suggests, an “Alt-az” mount is a simple two-axis device that tracks objects in the sky by moving in two directions: up/down (altitude) and left/right parallel to the horizon (azimuth).

Sky-Watcher AZ GTi

These mounts are a popular choice for beginners as they are incredibly easy to set-up: you simply have to level the tripod to the ground (most mounts come with a handy level bubble), input some data (day/time and GPS coordinates) and perform a simple star-alignment.

Some Alt-az mounts come with a built-in GPS system, so that the initial data input is no longer required. Besides, in most cases these mounts are relatively light and portable and are normally cheaper than other designs.

Apart from their standard version, Alt-az mounts come in several variants, the most famous being Dobsonian mounts. In this version, rather than on a tripod, the Alt-azimuth mount is fitted on a simple wooden platform placed directly on the ground, which rotates 360°.

This type of mount is typically cheaper and is extremely convenient as it allows for very large Newtonians at an affordable price.

Skywatcher Skyliner 350P Flex Tube SynScan GOTO Dobsonian Telescope

Alt-Az mounts work quite well for planetary imaging and visual astronomy but have some limitations when it comes to deep sky astrophotography.

This is because they do not compensate for Earth rotation, limiting the exposure times to 20-30 seconds. At longer exposures, “field rotation” becomes visible and the stars appear elongated, forming what is referred to as “star trails”.

While DSOs astrophotography is still possible on an Alt-az mount (many astrophotos on this blog are done with an Alt-az), an equatorial mount will guarantee way better results.

Equatorial mount. As mentioned before, if your main goal is deep sky astrophotography then you definitely need to invest in a good, sturdy, and precise equatorial mount.

Similar to an Alt-az, an EQ mount moves on two axes, one called right ascension (east/west) and the other called declination (north/south); the difference is that one of the axes, the right ascension, is aligned (parallel) to Earth’s rotational axis through a process called “Polar alignment”.   

When polar aligned, an Eq mount will compensate for Earth’s rotation while tracking an object in the sky, effectively cancelling the field rotation effect, and thus allowing for long-exposure photography, which is essential to get deep sky objects’ faintest details.

iOptron GEM45 German Equatorial Mount

One of the most important feature in Eq mounts is their maximum payload, which is the maximum weight they can support while tracking objects in the sky. As a rule of thumb, for astrophotography it is advised to use no more than 60-70% of the maximum payload to minimise tracking errors.

For example, if a mount has a maximum payload of 30 kg (66 lbs), it is recommended to load not more than 14 kg (31 lbs) worth of gear. This includes the telescope’s weight as well as all the other components such as the camera, the guiding system, and any other accessory.

For this reason, equatorial mounts tend to be larger and way heavier than Alt-az, which drastically reduces their portability, something to consider in case you have to bring your scope out at night.Also, Eq mounts are usually more expensive than comparable Alt-az mount and require important investments.

Expectations vs. reality

If you decide to be a visual astronomer, there is one last thing to keep in mind. And this one is probably the most important: you need to lower your expectations!

Observing the Moon, the Sun (only with the appropriate solar filter!) or planets with a telescope is a breath-taking experience. Viewing Saturn’s rings or Jupiter and its four larger moons is something you will never forget!

However, when it comes to faint deep sky objects, you need to be aware that our eyes are not as sensitive to light as a camera is, and the views will NEVER match the images we can produce with long exposure photography.

Due to the long distance and the impact of light pollution, deep sky objects such as nebulas or galaxies will look like fuzzy, featureless blobs (pretty much as if somebody sneezed on the eyepiece), even with the most powerful telescopes. The human eye is just incapable of capturing faint details or colours.

That said, objects like double stars or star clusters will deliver enchanting views with the right telescope. Observing under dark skies, far from light pollution helps getting better views, and some filters can be used to increase contrast in objects like nebulas or galaxies.

So lower your expectations and remember that you are looking at objects that are thousands or even millions of light years away! Astronomy has a steep learning curve, it requires a lot of patience, but it’s one of the most rewarding hobbies.

DSOs Astrophotography

What is it?

The term “Deep Sky Obects” (in short DSOs) refers to all the celestial bodies that are outside our Solar System, such as stars and star clusters, galaxies, and nebulas. DSOs astrophotography is the art of collecting these Lonely Photons and turn them into beautiful, colourful images.

Contrary to planetary imaging, DSOs astrophotography is severely affected by light pollution. Even though light pollution filters are getting more and more effective, nothing can replace a good dark sky!

The Bortle scale is a numeric measurement (1 to 9) of the night sky’s brightness due to the effects of light pollution; using a Bortle map is a useful tool to find the darkest sky in your area.

Most DSOs are seasonal and the best moment to observe or image them is when they are at their highest in the sky, as far as possible from the interference of atmosphere and light pollution.

Planning an observation in advance using a tool like “Stellarium” can help get the best results and avoid a lot of frustration!

What do you need?

You’d be surprised to know that the most important thing in DSO astrophotography is not the telescope! In fact, the main difference between planetary imaging and DSO astrophotography is that the latter heavily depends on an advanced EQ mount, beefy enough to support all your gear while maintaining a high level of precision. Here’s what’s needed for DSO AP:

The mount. DSO astrophotography works best with long exposure photography; these are single frames of long duration (1 to 5 min on average). In this range of time, even the slightest vibration or tracking inaccuracy will result in elongated stars, or even star trails, and blurred images.

A good quality EQ mount, such as one of the Sky-Watcher EQ or NEQ series, then becomes vital to load all the gear while also tracking the objects in the sky with accuracy. It must be remembered, when choosing an EQ mount, that is suggested to use only 60-70% of the mount’s maximum payload capacity.

The Sky-Watcher EQ6-R-Pro

Autoguiding. Even the best mounts, however, have some flaws and if you aim at perfection autoguiding is then essential. This works with a guide scope mounted on top of the main telescope and a camera, such as the ZWO ASI120MM, attached to it and connected to the mount with a cable.

Using a software called PHD2, the camera locks onto a star in proximity of the main target and communicates with the mount to keep that star, and therefore the main target, precisely in the field of view.

The telescope. Finally, it’s time to choose the telescope. Unfortunately, when it comes to DSOs there is not a one-size-fits-all solution: with the exception of Andromeda, galaxies are quite far away and need telescope with longer focal lengths, such as SCT or large-aperture reflectors. Large refractors work too but are generally quite long, heavy, and expensive.

Want to buy a telescope? Check out this guide: A complete guide to buying your first telescope

Nebulas, on the other hand, are closer to Earth and appear larger, thus requiring a telescope with a wide field of view, which is normally obtained with fast, short focal lengths.

In this case apochromatic refractors dominate the field! There are plenty of options on the market, but as a rule of thumb, refractors with 3 (triplets) or more glass elements provide the sharpest results. William Optics, Sky-Watcher and Explore Scientific are some of the most widely used brands.

The camera. When collecting hours and hours of data on a target using long exposures, the camera can get quite hot and the accumulated heat can affect the frames’ quality, or even damage the camera.

For this reason, many DSOs astrocameras come with a cooling system behind the sensor, which allows to keep a constant temperature throughout the night. Some models have an active cooling, and the temperature can be chosen via the capturing software. Altair Astro, ZWO and QHY produce the most common cooled astrocameras.

DSLR cameras are also widely used for DSO astrophotography, with some advantages such as portability (no need to bring a laptop around!), and their very wide field of view, which is great for capturing very large nebulas. Canon seems to rule the scene here but Nikon is always there fighting.

Computer. Stacking hundreds of DSO frames takes way more effort and time than stacking planetary videos. Software such PixInsight or Astro Pixel Processor can run for several hours before providing you with the stacked image. Therefore, in my opinion, a powerful desktop computer with no less than 16GB RAM, good graphic components, and A LOT of disk space, is a must have.

More gear. For refractors, especially those with two glass elements, a field flattener is necessary to counteract the field curvature of the optical system and improve edge sharpness. Some flatteners are also focal reducers, which make the scope faster and increase the field of view by reducing the scope’s focal length.

Filters can be real game changers in DSOs AP, particularly when shooting from light polluted areas such as cities. Light pollution filters are getting better every day and Optolong, IDAS and Baader, to name some, offer very good and reliable products. When shooting with mono cameras RGB and some narrowband filters lie HA, Sii and Oiii are needed to achieve the best results.

Those who have to take their telescope on a ride to their favourite locations will also need a power tank to power up all the gear. Some also use smart devices such as the ZWO ASIAIR Pro to control remotely with a phone or tablet all the gear, including the mount, the camera and the guide camera, the dew heater and many other electronic devices.

Finally, a Bahtinov mask is necessary to reach spot on focus whereas an electronic auto-focuser will keep the scope in focus as the temperature changes through the night.

An electronic filter wheel is useful when shooting in mono with different filters. Both the electronic focuser and filter wheel can be controlled remotely with the ZWO ASIAIR Pro.

ZWO ASIAIR Pro connected with ZWO guide cam and guide scope

How does it work?

As said, DSOs astrophotography works better with long exposures, which allow to capture even the faintest details of these distant objects. Acquisition software like SharpCap, N.I.N.A. or APT (there are plenty more!) go even further and present some interesting tools that help with polar alignment, calibration frames and more.

It is generally advised to collect several hours of data on each target to reduce the noise generated by the camera and enhance the level of details. Also, sometimes combining different set of data (ie Narrowband with broadband) can lead to interesting results.

Once acquired enough hours of data is time for stacking; there are several programs to do that but, personally, I find that PixInsight and APP do a great job. Although not mandatory, it is recommended to always use calibration frames, such as darks and flats, to subtract camera noise and lens’ imperfections from the final image.

Once stacked, the final frame is a dark, linear image that needs post-processing before it can be turned into a beautiful astrophoto. Here PixInsight has an advantage as it allows to do everything in one software with terrific results, although Photoshop or GIMP are valid alternatives.

The magic of post-processing: the Andromeda Galaxy (work in progress)

Regardless of the software, some of the basic techniques behind the magic include stretching the histogram to bring out colours and details, playing with curves to increase contrast, sharpening and colour balancing.  StarNet++ (now included in PixInsight) removes all the stars from a picture, allowing for more aggressive histogram stretching, whereas Topaz DenoiZe does a great job in removing noise and increase sharpness.

When it comes to DSO post-processing, there are so many ways and different techniques to obtain those Hubble-style pictures you see on the web or on dedicated forums.

YouTube in this context is the best school for all the tutorials available. Time, on the other hand, helps everyone find their own style and flow, bearing in mind that astrophotography is an endless learning curve.


Deep Sky Gallery


Planetary imaging

Planetary imaging is the branch of astrophotography that aims at capturing the Lonely Photons that travel from objects within our Solar System. It represents for many the entry point in astrophotography…we have all started with the Moon after all, haven’t we?

What is it?

Planetary imaging aims at capturing objects in our Solar System such as planets, the Moon or the Sun. This can be done from virtually anywhere for these objects are so close and bright that light pollution doesn’t have any impact on this kind of photography.

However, a crucial role in planetary imaging is played by what astronomers refer to as “seeing”. This is basically the effect of fast-changing, turbulent airflows in Earth’s atmosphere that can make an image look blurred or distorted.

When seeing is unstable it can vary rapidly, even within the same minute, inevitably affecting the final image. Fortunately, this is where a technique known as “Lucky imaging” comes in (more on this later).

Another critical aspect in planetary imaging is planning. Planets can get closer or farther away from Earth as they follow their orbits around the Sun thus the best time to image them is when they are at opposition (the closest approach to Earth).

Also, just like Earth the other planets also spin on their axis meaning that some features, such as Jupiter’s Great Red Spot, are not always visible from our position. Planning an observation in advance using a tool like “Stellarium” can help get the best results and avoid a lot of frustration!

Jupiter with the Great Red Spot in evidence

What do you need?

Generally speaking, planetary imaging requires less (and less expensive) gear compared to DSOs AP. A standard Alt-AZ mount will do the job just fine and planetary cameras don’t need cooling so they’re generally less expensive and easy to use. Here’s what you need for planetary imaging.

The telescope. While it’s possible to do AP without a telescope, I am a proud amateur astronomer so I can’t imagine doing it without one. First thing for me then is obviously the telescope.

As the planets are quite small, two things become fundamental when choosing a telescope for planetary imaging: focal length and aperture. Longer focal lengths (>2000mm) help capture more details on the planets’ surface whereas larger apertures (>200mm) resolve higher resolutions.

The telescopes that are more suited for planetary imaging are the SCT (Schmidt-Cassegrain Telescopes) although great results can be achieved also with Maksutov Cassegrains and Newtonian or Dobsonians with large apertures. Celestron, Meade, Sky-Watcher are some of the most common brands.

Want to buy a telescope? Check out this guide: A complete guide to buying your first telescope

The camera. The second thing to consider is the camera that will have to capture those pretty Lonely Photons. Different types of cameras can be used, with different results. Smartphone cameras are the simplest solution but produce lower-quality images compared to dedicated astrocameras, such as ZWO or QHY, or Digital single-lens reflex (DSLR) cameras, such as Canon or Nikon.

Laptop or computer. Another necessary piece of equipment is a laptop or computer to run all sort of software needed in AP: from data capturing to stacking, denoising or post-processing, there’s a software for anything! A good, fast laptop with at least 16 GB of RAM, good graphic components and A LOT OF space is essential.

More gear. Other helpful gear includes Barlow lenses, which multiplies the magnification and extends the scope’s focal length, UV/IR cut filters, to cut out unnecessary light that would otherwise affect image quality, and an atmospheric distortion corrector (ADC), useful to image targets that are low in the sky, where the effects of the atmosphere are more visible. For mono cameras, RGB filters are necessary too.

How does it work?

Celestron Evolution 8″ EdgeHD SCT paired with ZWO ADC, Televue Powermate x2.5, and ZWOASI 224MC-Pro.

In planetary imaging the best results are achieved through “Lucky imaging”, a technique used by most astronomers to balance the effect of bad seeing. This works with free software such as SharpCap or Firecapture that record videos rather than taking single shots, thus capturing hundreds of frames per second (fps).

The videos are then run in dedicated stacking software, such as Autostakkert or Registax, which analyse them and select only the best, sharpest frames, rejecting the rest. This, of course, increases the probability of capturing good frames.

Once this step is done, what we’re left with is a final stacked image which probably needs some adjustments. The free software Registax offers a “wavelet” functionality that does magic in pushing out surface details whereas for additional touches software like PixInsight, Photoshop or GIMP help get the best out of your images.