Last year I came to discover that astrophotography with the current generation of smartphones is perfectly within reach. I shared some of the results I reached using either the Samsung stock cam as a modified GCam on a Samsung Galaxy S20 FE. Later on I also discover the following blistering picture on Reddit:
The picture was also made with a Samsung S20 FE using the default cam app, and according to the original poster was made with 30s exposure and iso 3200 and the app in Pro mode. You’ll notice there is a small effect of star trails in this picture due to the large exposure time. He claims that the brightest spots are planets. I assume the creator is talking about the one left of the Pleiades and not the one down at the bottom left of the picture as that may well be Sirius. The picture was taken in Kerala, South India, on what I assume to be a quite dark location given the results he got.
My first telescope
After the death of my father I started to realize that I’ve been interested into astronomy since my teenager years. I had a book to teach me some basics and I remember at one stage I even made some drawings about my observations, for instance there was the famous 1997 Hale-Bopp comet in there! I also tried to do some observations using binoculars but I never came to own a telescope. So this year I decided to finally get on with that childhood dream…
For the first telescope I went low price. I knew it could be a disaster (and it also kind of was), but it allowed me to get into business and actually understand the things that you kind also read about if you spend some time before buying. I went on and bought a second hand National Geographic 90/900, tube only so no mounting was included.
While the picture above shows you the original telescope and mount, since I only had the tube but had a spare aluminum camera tripod I decided it shouldn’t be that hard to mount the tube on top of it. In my first tryout I had some issues with getting to see anything at all, but later on I guess those issues were related to a the SR6 oculair and not collecting enough light. The camera tripod, while very handy to use with cameras, is also a very bad mount for telescopes. The thing with telescopes is that the level of magnification is 50x, 100x or maybe far more depending on your telescope. It means that even the slightest handling of the telescope makes your view totally unstable and shaky. The mount was also not strong enough to hold the tube in place once you had tracked down something, it always kind of sank a bit lower in the end after you’ve vastened everything. Even breezes of wind made the telescope shake a little bit! The end verdict was that I learned that with telescopes, more expensive is mostly with a good reason. And even though I did get to view Saturn for example, I also realized that it was very painful to get it observed properly because the view never ever was was very stable, let alone you could take a decent picture from what you’re looking at. I realized telescopes mounts made a great deal of the experience and decided to upgrade the mount…
Telescope mounts
So what’s a decent mount anyway? Well for starters there are different types of telescope mounts. Overall there’re mostly categorized as altazimuth, equatorial or dobsonian mounts. For more advanced use cases there is also the so called Startracker and GoTo mounts, but they’re kind of developed on top of the earlier mentioned types.
Altazimuth mount
This mounting type is simple in use an therefor often recommended for starters. Basically you can move your telescope around 2 axis: up/down (what astronomers refer to as ‘altitude‘) and left/right (what is called the azimuth). Try to memorize the names of the axis since it’s also used in the coordinate system that tells you where to find stellar objects
The above picture shows the most basic altazimuth mount you can find. If you spend a bit more you’ll often find extra handles that allow you to do slow motion control for each axis. You’ll certainly appreciate this, once you have an object in focus. Know that due to the earth rotation objects may only stay in view for 1 or 2 minutes, and often less depending which magnification you’re using. Overall these mount or made of aluminum which makes them light and portable. The more expensive ones can be made of steel and mostly are made for heavier tubes while offering more stability. While good for entry level astronomers know that this type of mount is typically not chosen for photography. It can but given the fast movement of objects in your oculair you’ll have to settle for a short shutter time.
Equatorial mount
The equatorial mount is a slightly more complicated type of mount and therefor often not recommended as a starters mount. With the EQ mount the axis to move along with are called the declination and ascension axis. But there is one specialty, if you want to decently use this mount you need to get it properly aligned with Earth’s rotation axis.
You’re probable well aware that the Earth’s rotation axis goes straight through the Earth from the north to south the pole. From the place where you live that rotation axis is not right above your head but instead much lower, perhaps even at an altitude of 45°. By coincidence the Earth’s rotation axis goes though the Polaris star which can be easily found if you know where to look. Hence if you ever need to know how navigate north at night just look where Polaris is at the night sky in head into that direction. Now as I said earlier the EQ mount requires to be properly aligned with this axis. Look at the above picture to get a better understanding. Once you have reached that alignment you can adjust the declination control to kind of move away from polar axis. Rotate around the Earth’s rotation axis using the right ascension (RA) control. As you read this for the first time this may all seem a bit confusing, but it also kind of makes sense. The mount takes some practice to get used to it, but it also has some benefits. Since the telescope can now be adjusted along the Earth’s rotation axis just as the celestial objects seemingly do, all you need to do once you have an object in view is that you slightly adjust the ascension control over time to rotate your telescope along with Earth’s rotation. Therefore the EQ mount is really great for photography of deep sky objects that require long exposure times. The hassle however is that you need proper polar alignment which always takes some time to get right each time you take out your telescope. Furthermore on a half cloudy night, while the thing that you want to observe or shoot is perfectly in sight you make lack the view on the Polaris start and not be able to properly align your EQ mount. Within the EQ mount category there are many different variations and flavors. The differences to be found are in materials (aluminum vs steel), handles, weight, counterweights (which are used to keep everything in balance), slow motion control, ability to adopt to motor control, … The EQ mount is typically found on non entry level telescopes given they’re a bit more expensive and harder to use.
Dobsonian mount
Dobsonion mounts are specifically designed to hold the Dobsonion type of telescopes. It’s very simple in basis and is very similar in usage as with altazimuth mount: moving the telescopes goes along up/down (altitude) and left/right (azimuth) axis. The biggest difference is that Dobsonian mount don’t really have a tripod at all but instead come with a large and bulky construction often made in wood that is able to support heavy large telescopes.
The mount itself has at the base some kind of turntable which allow it to move along the azimuth axis. The telescope is vastened to the mount over a horizontal axis which allows the up/down movement that we need for altitude adjustments.
Overal telescopes on a Dobsonian mount tend to be less portable as the setup is large and heavy. However the usage of wood makes it still possible to move them from a safe storage room to the outside without sacrificing any stability. It also makes the mount cheaper and they’re easier to manufacture too.
GoTo mount
The GoTo mount isn’t really a new type of mounting. Generally speaking it is a motorized variant of one of the above types. Generally they’re controlled by a computer system or hand controller which dictates the mount where to point the telescope too. Most of the time they can also track celestial objects which can be handy for your observations but that aside they’re also very useful for astrophotography since locking the object in sight allows for longer exposure times. Know though that if you’re really interested in deep-sky objects the motorized equatorial mount is still much favored over the altazimuth mount since it only has to move along one axis, the RA axis. The added features of a GoTo mount however doesn’t come cheap, expect to pay premium prices compared to non-motorized mount. Also always keep in mind that for those long exposure shots the mount needs to be very stable, so it’s always better to go for a bulkier mount, but know that this also adds up to the total cost.
Star trackers
Start trackers are kind of a miniaturized versions of the GoTo mount. They’re similarly computer controlled but are targeted at holding camera devices mostly, maybe an additional telelens or small refractor, but never any serious sized telescope. So while they’re not useful for observing things, given their tracking abilities makes that they’re quite useful for long exposure shots of the night sky. They’re more portable than GoTo’s and also cheaper, but expect to still pay few hundreds of Euros for a device that mostly used for the specific purpose of photography.
Telescope types
So I was stuck with this refractor type of telescope and a handful different types of mounts that come in various flavors onto the market and each having their own kind of pros and cons. What to choose? And what’s compatible? Do I go for low price or heavy duty and feature rich? As I explored the second hand marked and reading reviews I quickly came to understand that willing to have long exposure shots mostly requires an EQ type of GoTo mount with tracking abilities. I then realized they don’t come at all, and that any decent mount can cost you € 1000 easily. So maybe I should lower my expectations a bit and just go for a stable mount and just settle for short exposure shots. In this case however you seems to get in a different kind of ballpark as suddenly the EQ mount is no longer ‘required’ and you can actually choose the cheaper altazimuth or Dobsonian mounts. After investigating in that area a bit about what makes a decent and stable mount mostly what you should avoid is that those aluminum ones. Go for a decent steel mounting. The thing is that I couldn’t really find any decent on the second hand market, so maybe I should rather ditch the current telescope tube and settle for a complete setup instead? I come across less than a handful decent altazimuth and EQ mounts but they mostly came together with a Newtonian telescope that was not of the best quality. Instead there were quite a few Dobsonian telescope to choose from, but they looked so clumsy to me. But maybe that’s just because I’m still not very familiar with the different types of telescopes. So what’s up with that? Well I was already kind of aware about the refractor types which basically we all so in our imagination when asked about how a telescope looks like. And then there are the other which for me all looked pretty similar, except maybe in some cases with some extra mirrors for extra amplification. Well it turns out it’s not that simple. But first something about the basics.
Telescope basics
Light travels into the telescope through the objective or aperture and reaches the eye through what’s called the oculair or eyepiece. Tubes have different lengths and widths and that’s not without reason. Inside the telescope light may travel across flat or parabolic mirrors, which do have an effect on the end result. All combined a telescope will have a certain level of magnification, the higher the magnification the bigger you get something to show up that’s too small to be picked up by the naked eye. It also narrows the view.
An important rule to understand is that magnification is limited by the amount of light that can be collected at the aperture (= the main lens or mirror). Another interesting aspect is the focal length of the objective (mostly referred to as the focal length of the telescope given they’re fixed and can’t be upgraded) and the focal length of the eyepiece. The formula is simple:
magnification power = telescope focal length / eyepiece focal length
Know that the telescope focal length is fixed but eyepieces can be exchanged so you actually have a choice in what level of magnification you want to use. For example your telescope may well come with 20mm and 10mm eyepieces (the mm here is not the diameter of the eyepieces but instead their focal length!) suited for different kinds magnification and thus different kinds of observations. In case this telescopes focal length is 800mm, this would result in a magnification of respectively 40x and 80x.
But as I said the magnification is also tied to the aperture and which defines the amount of light collected. If there is not enough light falling into your telescope the end result will be that you don’t see anything at all. Doubling the level of magnification actually reduces the brightness of the image by a factor of 4. Vice versa, if you double the aperture it also means you’ll collect 4 times as much light which result in a brighter image. So the theoretical level of magnification is actually limited by the aperture. This is referred to as the “highest useful magnification” and can be calculated by multiplying the diameter size of the aperture (in inches) by 50 times. For a 6 inch telescope that number will by x300. When you reach this limit you’ll have a very dim image that’s not worth much. There is also a lower bound, this is referred to as the “lowest useful magnification“. It can be calculated by multiplying the diameter size of the aperture (in inches) by 3 to 4 times. A 6 inch telescope will have a lower magnification boundary of about x18 to x24. The lower the magnification the wider the field of view. While magnification is important don’t stare yourself blind at it. You may think that the more magnification your telescope has the better it allows to observe objects in detail. However having a wider field of view may also play a role for example to observe large entities such as the Andromeda galaxy. Aperture is plays an important role as it will tell you something about the amount of light collected and reaching your eyepiece and may make a crucial difference when comparing telescopes with similar magnification levels. It’s perfectly possible that having a smaller level of magnification but a higher aperture will result in a better viewing experience.
The weather conditions also play a role, and we’re not speaking about cloudy nights here, but really about the atmosphere. Sometimes there is more turbulence in the atmosphere which may make you image a bit fuzzy and dim. It may impact your level of magnification and you may need to settle for oculairs with bigger focal lengths.
The focal ratio of your telescope differentiates “slow” and “fast” telescope from each other. It can be calculated as following:
focal ratio = telescope focal length / aperture
Image you have a telescope with a focal length of 500 and an aperture of 50, in this case your f-ratio will be 10. Take another telescope with the same focal length but with an aperture of 100 than the f-ratio will be 5 instead.
Refractor telescope
This is the classical type of telescope that we all think off when asked for. The light enters the telescope through the objective lens. The rays of light converge at the focal point and makes it way through the eyepiece (oculair) out of the telescope again. With reflectors if you need a long focal point for higher levels of magnification you’ll end up with longer telescope tubes too. A focal length of 900mm will give you a tube of at least one meter. The quality of the lenses may play an important role in the image quality.
Reflector telescope
With reflectors it becomes a bit more complicated. Here the light enter the telescope directly, there is not objective lens. The light travels through the entire scope only to reach a reflective mirror at the opposite side of where it entered the scope. This mirror is the primary mirror and it features will tell you something about the quality of the scope. We’ll come back on this on a few moments. Next, light is bounced back onto the secondary mirror which bounces it again but this time perpendicular to the scopes orientation. While with the refractor you gaze more or less directly through the telescope, with reflectors you actually more or less sit on top of them. A small benefit of the reflector is that the focal point is beyond the second mirror and therefor a part of the converging path is perpendicular to the reflected light from the primary mirror. Hence the tube can be a bit shorter compared to a refractor to meet the same focal length. Some telescope vendors opt for spherical primary mirror to further increase the focal length for the same sized tube, but mostly this result in bad image quality and in general those scopes are not recommended. Parabolic mirrors are preferred as they’re more precise and have only one focal point. This will result in clearer images. Know that when the mirror is of bad quality the image is not always very clear, may give artifacts and you may have issues with higher levels magnification which as kind of a pitty for the price that you paid.
Another thing with the reflector scopes is that they mostly have a larger aperture which helps tremendously.
Other telescope variants
I’ve only highlighted the two main telescope categories. Throughout the years many more designs have been introduced. The classical Newtonian reflector has been adopted to even have more mirrors inside to further reduce, and also refractors have been adopted to become more compact without sacrificing the viewing experience. There are some many variants that it would take me forever going through them all and discuss their pros and cons. Even for the telescopes that I did include in this article there are things that I didn’t want to get into as it will take us to far away.
My second telescope
So with all of that information in mind I went on and on to see which of the second hand offers would suit me the best. As I already realized earlier I might have been chasing the wrong idea. I didn’t want to spend € 500 to € 1000 for a motorized EQ mount on a hobby that I’m just tacking up once in a while, because not being able to take long exposure shots is maybe not the end of the world either. I also didn’t want to make the mistake again to settle for something that is generally known within the community as bad quality. As I understood many great sub € 500 telescopes were actually of the Dobsonian type. There are off course other telescopes within that price range that they compete with, still mostly Dobsonians came out best in the reviews of trusted reviewing sources. Here is why:
- handling: the Dobsonian is easy to use, moving it feels very natural and doesn’t need a lot of practice to get used to it. EQ mounts are mostly harder to learn and take some time to setup.
- steadiness: the mounting is very steady, it’s in a whole different league compared to aluminum lightweight tripods
- aperture: refractors are something referred to as light buckets. Their design allows them to collect more ligt compared to similarly priced refractors which can come in handy when increasing the level of magnification
- parabolic mirror: in the lower end segment you need to be careful about the mirrors that are used in the reflective telescope. I noticed quite a few Newtonian reflectors mounted on either altazimuth or EQ mounts that come with a spherical primary mirror. Somehow that seems to be less the issue for Dobsonians in that price area.
- price: while looking big and expensive, the contrary is often true. Dobsonians are very competitive even in the sub € 500 price market
One of the offers I could find is the Sky-Watcher Classic 150P.
The Classic 150P has a 150mm (6 inch) aperture. According to the Sky-watcher website that’s a 232% increase in brightness compared to a 100mm refractor. It should yield even better results compared to the 90mm National Geographic refractor that I purchased earlier. Another nice comparison: it’s 460 times brighter than the human eye! The maximum magnification level is around x300. It comes with the typical stable Dobsonian mount and handy tension controlled handles to move it smoothly but steady. It features a parabolic primary mirror, which stands for decent image quality. The focal length is 1200mm which is also quite an increase compared to the 90/900 refractor. The F-ratio is 7.9 which puts it in between narrow and wide field telescopes. The scope comes with 2 eyepieces that have a either a 25mm or 10mm focal length. They result in a magnification of respectively x48 and x120. Maybe one downside is that it may have also been equipped with a 6mm eyepiece too which would settle use with a magnification of x200 which it still well within the limits of this telescope. Any other eyepiece with an even shorter focal length would probable put you at or beyond the boundaries of what this scope can handle, so for those we want more there are also the 200P and 250P who respectively have a maximum level of magnification of x400 and x500, but off course at a more steep price. The Classic 150P settles at about € 430 on the Sky-Watcher website, however I was able to get one in perfect condition for € 230 which seemed to be a good deal and finally decided that would be it.
First astro shot
So I was finally settled for my first decent observations. I didn’t had the best weather until now, however I did succeed to get a glimpse of Saturn and I even got to record it with my Samsung FE20 smartphone holding it by hand! This by itself was certainly not within reach when I used the NG 90/900 refractor and alu tripod. I converted the video into a gif animation and I cropped it to make it better fit on this blog site. Through the telescope it does look maybe a bit smaller but much sharper. You can see the smartphone has some issues getting it’s focus correct, which is not that strange given I’m holding it by hand. The eyepiece in use is the 10mm one. As I mentioned earlier this gives my x120 magnification. Here is that shot:
For now I’ll have to deal with this result. In a followed article I’ll finally come to the photography part which was initially where it all started with. But before we got there we had to make a little detour so that you understand to road I had taken. At least I hope you enjoyed and maybe learned something along the way. Stay tuned for more.
after hours coding 