Sky Watcher Evostar 72 ED – not only for astronomers

Sky Watcher Evostar 72 ED – not only for astronomers
30 May 2021
Arkadiusz Olech

1. Evostar 72 ED in theory

There are a lot of spotting scopes available on the market but when you start looking at them closely you can find that many of them come with some limitations. The first problem you might encounter concerns their size and, partially connected to that, the price tag.

Let's assume you are not interested either in pocket-sized 50 mm midgets or in more stationary 100 mm telescopes. That limiting factor leaves two types of scopes to be chosen from: the 60-65 mm and the 80-85 mm. Of course the smaller a device the lower its price tag, and these might start even from 500 PLN. Still, I don't think you can find a good quality objective lens and zoom eyepiece at that price point; to be honest 500 PLN wouldn't be enough to produce a good zoom eyepiece, let alone a telescope itself. If you look at prices of top-of-the-range spotting scopes and their accessories you can find out that for example just a case for the Swarovski Optic spotting scope might cost as much as... 1100 PLN. If you want to buy a telescope for half of that sum you really shouldn't expect much.

Sky Watcher Evostar 72 ED – not only for astronomers - Evostar 72 ED in theory

Not wanting to exaggerate we claim in all responsibility that, in order to enjoy good quality images in a 60-65 mm spotting scope you have to spend at least about 2000 PLN. There are several instruments worth recommending in this size class like the Delta Optical Titanium 65ED II or the Celestron Regal M2 65ED.

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If you are interested in a brighter image provided by a bigger objective lens you have to look at the 80-85 mm class and a sensible instrument might cost you about 2500-3000 PLN. Mind you, on principle in the box you get just a zoom eyepiece with a narrow field of view. If you want to get rid of that limitation you have to choose a Regala M2 80ED class telescope with an open 1.25” class eyepiece mounting system but its price point reaches almost 4000 PLN. A good quality 80-85 mm telescope with a wide angle zoom eyepiece might cost you even more, about 5000-6500 PLN.

The situation is not so rosy, right? Well, think again. What would you say if I told you that for as much as 2000 PLN you can buy a device brighter than 65 mm and with a possibility of attaching different eyepieces? The Sky Watcher Evostar 72 mm seems to be the answer to all the questions asked in the introduction and a piece of equipment you are looking for.

Sky Watcher Evostar 72 ED – not only for astronomers - Evostar 72 ED in theory

Most of you would say: 'hey, it's already an astronomic telescope'. I answer: in particular you're right but overall it is a lot more than that. The Evostar might start as an astronomic telescope but it might be turned into a fully-fledged observation telescope, something used not only by astronomy fans but also by casual nature observers or sports shooters.

Like in a case of every good observation telescope, an objective lens lies at the heart of the Evostar 72 mm. Here you deal with a doublet made of Schott crown glass and a low dispersion ED glass. The Sky Watcher company doesn't say what type of ED glass you get but the objective is supposed to ensure apochromatic correction and it certainly helps with visual observations even if it doesn't concern astrophotography. The objective is 72 mm in diameter - at the very beginning you are in a better position than users of 60-65 mm class telescopes by a factor ranging from almost 23 to 44%. It is really a lot. What's more, the objective features anti-reflection Metallic High-Transmission Coating (MHC) and their loss of light on one air-to-glass surface shouldn't exceed 0.5%.

Sky Watcher Evostar 72 ED – not only for astronomers - Evostar 72 ED in theory

The objective lens comes with the 420 mm focal length (and a quite efficient aperture fastness of f/5.8). It is closed in a metal cassis that ends from one side with a solid dew shield (which people with photographic bend might call a build-in sunshield or a hood) and on the other side you see an eyepiece extension tube as big as 2 inches. What's more, that extension tube comes with an efficient dual-speed (1:10) focuser. Everything weighs 1.9 kilograms and is 41 cm long. The tube also has a holder to attach an optional finderscope.

Sky Watcher Evostar 72 ED – not only for astronomers - Evostar 72 ED in theory

The telescope comes with a very stylish, aluminum case and a dovetail bar that allows you to put this instrument both on an equatorial mount or on an ordinary photographic tripod.

Sky Watcher Evostar 72 ED – not only for astronomers - Evostar 72 ED in theory

If you add an eyepiece to that, you get just an astronomic telescope; when you try to use it to observe something on the ground it has two flaws. Firstly, with this configuration the images are upside down; secondly, it is a straight telescope so, in order to look through it you need some gymnastics near a tripod.

Both these problems can be sloved with appropriate diagonals. The cheapest ones are 90-degree mirror diagonals, available in two sizes, 1.25” and 2”, but they solve the problem only partially. Of course they improve observation comfort but images still remain reversed, not upside-down but left to right. At the same time cheaper diagonals come with a mirror covered by just simple aluminum coatings so losses of light might reach even 10%.

Sky Watcher Evostar 72 ED – not only for astronomers - Evostar 72 ED in theory
1. Cheap 90 deg and 45 deg 1.25-inch prism diagonals.

A prism diagonal, most often based on Amici roof prism, is a better solution. In this case you can choose not only between 1.25” and 2” devices but also between 90-degree angle and 45-degree angle of bending the optical axis. You get simple, bright images - it's enough you cover the prism of the diagonal with high-quality anti-reflection coatings to guarantee losses of light of less than 2%, including the glass absorbtion rate.

Sky Watcher Evostar 72 ED – not only for astronomers - Evostar 72 ED in theory
1.25-inch prism Baader Planetarium diagonal.

How much you would have to pay for it? Not much. The cheapest 1.25” prism diagonals co-produced by Delta Optical and GSO cost 75 PLN. Sky Watcher diagonals are less than two times more expensive. Are they worth the extra money? To be honest, even though these diagonals have good price/quality ratio, in my humble opinion they are a bit too weak for excellent Evostar optics. When I tested the telescope I used the 45-degree Baader Planetarium 1.25” diagonal. It's true you have to spend 300 PLN on it but its build quality is truly superior and it features better coatings; anyway, when joined with the Evostar, its performance was really exemplary. In fact, both these devices seemed to be created for each other. During nighttime observations I noticed that cheaper diagonals allowed a higher level of astigmatism but when I attached the more expensive Baader stars stopped sparkling and became more point-like.

Sky Watcher Evostar 72 ED – not only for astronomers - Evostar 72 ED in theory2-inch star diagonal Baader Planetarium might cost you as much as 1099 PLN.

Of course, in order to experience the peak of the Evostar's performance you should buy a 2” prism diagonal; the only problem is that you have to spend about 1000 PLN on it so we would recommend that option only to the biggest fans of optics who don't have to econimize. A 1.25” diagonal and a whole bunch of eyepieces, connected to that standard, are more than enough for the uses we are going to recommend the Evostar for. Still, you should remember you have to buy a 2” to 1.25” adapter; fortunately, it doesn't cost a lot.

Sky Watcher Evostar 72 ED – not only for astronomers - Evostar 72 ED in theory2” to 1.25” eyepiece adapter produced by DO-GSO with additional T2 thread.

The final effect is such that, when you combine the Evostar 72 mm with a good quality Baader 1.25” prism diagonal you are still within the 2000 PLN budget and you get an excellent telescope with an objective lens bigger than in the case of 60-65 mm class instruments. Mind you, with an open system allowing you to use different eyepieces your choice in this area is really impressive.

If you want to economize you might just add three plossl-type 4-element eyepieces and such a set would cost you about 300-400 PLN. The first of these should have the 25-30 mm focal length that allows you to reach magnifications of 14-16.8x with a significant field of view, amounting to 3.0-3.5 degrees. The second eyepiece should be an instrument with a focal length of about 15 mm and it allows you a magnification of around 30x and a field of view wider than 1.5 degrees.

The eyepiece with the shortest focal length might be a problem here. First, you have to answer a question: what is the highest magnification value that satisfies your needs. In case of 60-65 mm spotting scopes producers are able to reach a level of 45-50x, and it is about 60x when it comes to the 80-85 mm class. In our opinion good optics of the Evostar 72 mm allows you to reach magnifications of 70-80x and over 100x for those less discriminating when it comes to image quality. We think a 6 or 5 mm eyepiece that will provide magnification of 70 or 84x is a really good choice.

Sky Watcher Evostar 72 ED – not only for astronomers - Evostar 72 ED in theory

Unfortunately in this case a simple plossl construction might not be that efficient and for two reasons. First, plossl devices have a field of view of about 50 degrees; when you combine it with a magnification of about 80 times you get too narrow a field for the whole system. Second, and perhaps even more important, the eye relief distance of a 5-6 mm plossl amounts to about 4 mm – it means you will have to press your eye very close to the eyepiece and practically sweep it with your lashes.

The problem might be avoided to some extend if you buy a Barlow 2x lens. It is a diverging system that you insert between an objective lens and an eyepiece, increasing the effective focal length, nothing else but an equivalent of a photographic teleconverter. Such a lens costs about 100 PLN so its price is comparable to that of a plossl so, instead of buying a third plossl with the shortest focal length you might purchase a Barlow lens. The result will be such that, if you combine it with the 15 mm plossl you will get a magnification of 56x instead of 28x. The eye relief distance will remain the same as for the 15 mm eyepiece, so 10-11 mm, a clear advantage over the plossl with a shorter focal length. Still image quality will deteriorate - adding a cheap barlow to the system always decreases its performance.

Fortunately there is other solution, better but more financially demanding. In the text about the Delta Optical 50ED I recommended a series of 5-element Sky Watcher SWA-58 eyepieces so let's be consistent and say that they also supplement the Evostar in an excellent way. Instead of paying 100-150 PLN for a short focal length plossl you can buy the SWA-58 eyepiece. You gain a wider field of view as it amounts to 58 deg and a better eye relief distance which, even in short focal length eyepieces from this series, is 16 mm. What's more, you might also enjoy a wide rage of focal lengths because in the class below 10 mm you get as many as 9 models available. Of course these with 2.5 and 3.2 mm focal lengths don't count because they are a bit of an exaggeration but the 4 mm model can already be taken into account (with the magnification of 105x). The devices with 5, 6, and 7 mm are completely recommendable and they ensure magnifications of 84, 70, and 60x respectively – as you like it.

Sky Watcher Evostar 72 ED – not only for astronomers - Evostar 72 ED in theory
Super-plossl Sky Watcher SWA-58 eyepieces 20, 6, and 7 mm.

One small digression – if you already decide on a 4-5 mm eyepiece, do remember to use a really stable tripod with a high-quality head. If you lack such a tripod and you don't want to buy it, it's better and safer to stick to 6-7 mm eyepieces.

Of course if you want to enjoy a good image quality and a sensible field of view, even at longer focal lengths, it's better to avoid any plossl devices. I've written about the 15 mm plossl model, providing the 28x magnification. Its eye relief is also rather short, amounting to 10-11 mm so hardly comfortable for people wearing glasses. Instead, you might choose the SWA-58 15 mm and enjoy the 16 mm eye relief distance along with a wider field of view.

In the case of an eyepiece of 25-30 mm class you might be tempted to economize a bit and still choose a plossl because the problems with a short eye relief distance disappear. Still if you want to enjoy a better image quality and a wider field of view you should get interested in the SWA-58 mm model with a focal length of 25 mm.

Sky Watcher Evostar 72 ED – not only for astronomers - Evostar 72 ED in theory

As you see, the topic concerning the pros and cons of different eyepiece is really wide; in fact you could write a whole essay about it. My first conclusion is such that if you want to economize you can always buy ordinary plossl eyepieces that can still provide a lot of fun. Still, as I recommended you a slight increase of your spending budget in case of diagonals and buying a more expensive Baader, here I also suggest a purchase of three SWA-58 eyepieces with the following focal legnths: 25 mm, 15 mm and something ranging from 4 to 7 mm. These eyepieces really fit the Evostar 72 mm very well when it comes to the quality of images, the comfort of observation, and the price.

Before we progress to the results of our practice test of the Evostar 72 mm let's sum up this section. If you want to buy the Evostar with a prism diagonal 1.25” Baader Planetarium, an adapter, and three plossl or SWA-58 eyepieces, you have to take into account an expenditure of 2500- 3000 PLN. For this amount of money you get equipment which, compared to classic 60-65 mm spotting scopes, offers you only advantages. It's true that it costs almost that much but it has a bigger objective lens, a wider field of view, and a wider range of magnifications that might be configured by the user. What's more, after buying a cheap adapter you can attach to it any reflex camera or mirrorless camera you want and enjoy a telephoto lens with 420 mm focal length and an aperture as efficient as f/5.8.

Not enough? For 1299 PLN you can buy a dedicated 0.85x focal length reducer that also flattens the field of view. With that device you get a sensibly corrected astrograph with a focal length of 357 mm and f/4.96 aperture. Of course you shouldn't fool yourself – this instrument will be hardly outstanding. After all there is a reason behind these expensive triplets or quatruplets, dedicated for astrophotography on the market. Still, you can't deny that you deal here with a very universal set, bought at an affordable price, which can be turned into a portable astronomic refractor, a fully-fledged spotting scope, a telephoto lens, and an astrography instrument for the begginers, as you need it.

Sky Watcher Evostar 72 ED – not only for astronomers - Evostar 72 ED in theory

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