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Vortex have had a rich selection of binoculars in their line-up from the very beginning, with more than a dozen model lines at different price-points. In the case of spotting scopes such a rich offer is impossible for obvious reasons – it would be difficult and pretty useless too. Small wonder you deal here with just three segments.

Diamondback spotting scopes are the cheapest, with prices starting from 500 USD, then you get more expensive Vipers HD and finally you reach the most expensive, high-end Razor HD series with the highest number of models available. Still, if you plan to buy an 85 mm Razor model you have to spend as much as 2000 USD on it.

When it comes to binoculars, Vipers HD models enjoy a good opinion and are fairly popular on the market, no matter what variant you mean. Also all of them have fared well in our tests as their price/performance ratio has always been very favourable. In short, their performance is very close to that of top-of-the-range devices and still they remain several times cheaper - small wonder they have been recommended on our forum time and again, also in comment section of our tests.

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That's why we really fancied a test of a device from the Vortex Viper HD spotting scopes series just to see whether its properties are as excellent as the properties of the binoculars. There are 65 and 85 mm models offered in strait or angled versions and we decided to borrow the angled Vortex Viper HD 20- 60×85 which suggested retail price, as stated on the official site of the producers, amounts to 1349 USD; in Poland that spotter is available for 3500 PLN. It is noticeably higher than prices of binoculars from that series but you have to remember that you deal here with a big objective lens coming with an optically complex zoom eyepiece.

What are the most important features of the Vortex's optical and mechanical build? When it comes to the objective lens, the producers boast of an HD (high density) system, which means in this case high quality extra-low dispersion glass. The number of reflections indicates that you deal here with three elements positioned in two groups. Of course there are more elements from this side of the instrument because more or less in its middle you find a case with a focusing element.

When it comes to prisms, the producers state they implemented the Porro prisms system. Classic Porro can be found in straight models and the angled model most likely features an additional prism that directs the light path at an angle of 45 degrees from the main axis. Unfortunately, we didn't manage to find out anything about optical construction of the eyepiece but we know that it offers magnification from 20 to 60x and its field of view changes from 1.92 to 0.95 of a degree. Using the tangent formula you can calculate that the range of the fields of view of the eyepiece amounts to 37-53 degrees. Such values are rather low – typically in spotting scope zoom eyepieces you get a field of 40-60 degrees, some producers even happen to offer 50-70 degees.

The producers declare that they employ XR multi-coatings that are supposed to cover all air-to-glass surfaces. Additionally inner elements are covered by hydrophobic ArmorTek coatings, protecting the exterior lenses of the instrument from dirt, humidity, and scratches. What's interesting, the producers also mention dielectric coating - most probably dielectric reflection layer is located at the surface of the additional prism placed behind the Porro system.

The spotting scope is sealed and waterproof. What's more, its tube is argon filled in order to make the instrument resistant to internal fogging even if you move through extreme changes in temperatures.

The eyepiece is fixed to the mount in a unique way, characteristic just for the Viper HD series. It means you can't use eyepieces of other producers or astronomic 1.25 inch standard eyepieces. In Vortex line-up you find just one other eyepiece for this instrument which comes with a grid. It also features magnification of 33.5x, a field of view of 1.93 degrees (and an apparent field of view of as much as 60 degrees), and a very comfortable eye relief, amouting to 18 mm. That eyepiece comes with a price tag of 290 USD and it can be used only with spotting scope that have an objective lens of 85 mm. It doesn't cooperate with smaller models, with a 65 mm objective and it's a pity the producers didn't decide to offer more wide-anlge fixed-focal eyepieces. After all with a prime you almost always get a better image quality and a bigger field of view with edges corrected in a superior way.

The helical focusing system is controlled by a large focus collar covered by rubber armour with ribs. It is situated between prisms and the objective. It moves smoothly and is well damped but personally, I think an external screw with two gear ratios is a better solution when it comes to the highest maginification values. You can control it just putting one finger on it and the tube doesn't vibrate so much as it does when you deal with one big collar with one gear. The collar's range is set in such a way that it allows you observations in a range from 10-11 meters to infinity. In order to cover that range you have to turn the collar through an angle of as much as 780 degrees.

Right next to the focusing collar you find also a tripod mount collar joined with the metal ring. The ring moves and it comes with a block, allowing you to rotate the spotting scope along its main optical axis. That rotation is very smooth and you get a click stop every 45 degrees.

From the mechanical point of view the scope presents itself very well. Protective rubber armour is of very high quality – its properly rough surface sticks to your hands very well. It isn't loose in any place, covering the device in a great way. All mechanisms perform as they should. A retractable build-in sunshade can be extended very smoothly, revealing a metal chasis of the spotting scope and protecting the front element which hides inside the optical tube over 5 cm deep. The tripod mount collar, mentioned above, and the focusing collar perform in an exemplary manner. The mount and its interior, along with area around the prisms, are black and matt, without any slits or gaps. As you see, you deal here with a seamlessly weather-sealed instrument.

A zoom eyepiece which is a part of the box set, also impresses with its build quality. Its main parts are made of metal and the magnification ring is covered by ribbed rubber that sticks to your fingers well. The magnification is done very smoothly, without any sudden jumps but with proper resistance. The eyepiece ends with a rubberized eyecup which six-point height regulation. It ensures you comfort of observations, enhanced by long eye relief distance that, depending on magnification, changes from 17.8 to 19.6 mm. Such values ensure you very enjoyable observations even if you wear eyeglasses.

If you illuminate the interior of the tube with a beam of bright light you can find out two things. Firstly, coatings on all air-to-glass surfaces, prisms included, shimmer light green. Secondly, the producers took care to blacken the interior of the scope and they kept it very clean. Inside you can admire smooth, matt, black surfaces divided by several apertures. The area around the prisms on the bottom of the tube is also dark and matt. Still if you want to have some reservations you should look at the rim of the case keeping the focusing element in place – in our device it was a bit scratched and too shiny.

When it comes to standard accessories, apart from the zoom eyepiece with caps described above, you also get a rubberized objective cap, a cap for the eyepiece mount, an objective lens cover, a custom fitted case for the whole instrument, and a cleaning cloth.

As we finished describing basic parameters and mechanical properties of the Viper HD 20- 60×85 let's move to the best part - the practical performance of its optics.

The Pentax PF 80ED-A spotting scope was chosen for comparison's sake. It is equipped with three eyepieces: the 30 mm Plossl Vixen with magnification of 17.3x and an apparent field of view of 50 degrees, the 13 mm Vixen LVW, with magnification of 39.9x and an apparent field of view of 65 degrees, and the 8 mm Baader Hyperion, with magnification of 64.8x and a field of 68 degrees. The Vortex spotting scope was tested at 20, 40 and 60x magnification.

A close look at images, offered by the Viper HD 20-60×85 suggest that indeed high quality low dispersion glass can be found inside. Images are not completely devoid of chromatic aberration but it is not a serious problem no matter what magnification you employ. It will be the most bothersome at 20×, being noticeable in the centre and medium on the very edge. In our classification by points, used in the case of binoculars, the spotter would get 5.5 points in this category. When you pass to 40× aberration decreases both in the centre and on the edge of the field – as a result this device would score at least 7.5. With 60× magnification you can observe an interesting phenomenon – aberration increases slightly in the centre but it decreases by the same degree on the edge of the field so the score would remain the same.

When it comes to distortion we simply didn't know what to expect. On the one hand you deal with a narrow field of view and it makes correcting that aberration easier; on the other hand its correction across the whole focal lengths range is never easy. Still we have to say the Vortex performs here very well. At 20× you can't notice any distortion at all, at 40× you can spot very slight 'pincushion' and at 60× it increases a bit but still can be called slight. In this category the Vortex simply knocks out the Pentax and the fixed-focal eyepieces. The Plossl had significant pincushion distortion and the Hyperion featured distinct barrel deformations. It seems the Vixen LVW fared the best of these three.

When you deal with an eyepiece with a narrow field of view you can expect good sharpness across the whole field. The eyepiece of the Viper doesn't have any serious difficulties in this area although its performance is not perfect. Using 20× magnification you can notice very slight decrease of sharpness, visible only in the last 5-10% of the field of view. In the middle of the focal range the result of the eyepiece is practically the same. The situation changes only at 60× where the level of sharpness goes down a bit more, encompassing the last 10-15% of the field of view.

If you compare the Vortex Viper HD 20–60×85 with the Pentax and its fixed-focal eyepieces you find out its task was very difficult. What are the conclusions? We noticed a difference in colouring of images. The Pentax provides colder hues, perhaps slightly tinted blue. The Vortex, on the other hand, offers warmer, slightly yellowish images. I admit I found the Vortex images more pleasing to the eye.

Of course Pentax fixed focal length eyepieces knocked out the eyepiece of the Viper when it comes to the field of view. Even the 50-degree Plossl prevailed over the Vortex construction. It is clear that good quality prime eyepieces are way better – mind you I didn't even touch top-of-the-range, expensive Petnax XW eyepieces, dedicated especially for Pentax spotting scopes, with fields of view amounting to 70 degrees.

It is also hardly a surprise that primes provide images that, overall, seem sharper in the centre and are a tad better contrasted. The biggest differences you could spot at both ends of focal range and the least pronounced are in the middle. It seems that, when it comes to the Viper, the area close to 40× provides the nicest images and, generally, all optical aberrations are corrected at that place the best.

We also took photos of the exit pupil in order to assess its shape and number of reflections near it; below you can find its images taken at 20×, 40×, and 60× magnifications.

In every case the pupil is neither egg-shaped nor eliptic but as round as it should. Still we think the area around it could have been darker – a lighter ring sticks out at once and its diameter and intensity changes with the change of magnification. Once again the best results can be observed near the middle of the focal range of the eyepiece.

Then we tested the scope at night in order to show how the optics of the Viper deals with astigmatism, coma, and brightness loss on the edge of the field. We admit we set the standards very high - after all an eyepiece with a narrow field of view has to be corrected perfectly well, otherwise we might criticize it rather harshly.

Still we can say that the eyepiece definitely passed our test with flying colours. We didn't notice any trace of coma or brightness loss practically across the whole field of view, no matter what magnification we employed. Images or stars were point-like even close to the diaphragm. If we wanted to allot poins like in our tests of binoculars then at 20× the result would reach a maximum level of 10 points and at higher magnifications it would amount to 9-9.5 points.

When it comes to astigmatism the situation is hardly perfect but we didn't expect miracles from a zoom eyepiece in this category. At 20× astigmatism is the highest and here we would give the Vortex 6 out of 10. The best point-like shape of stars in the field centre can be observed at 40× and here the tested device woud get 8 points. Passing to the maximum magnification astigmatism increases a bit so our score would drop to 7.5 points.

To sum up we can say that the Vortex Viper HD 20–60×85 is a spotting scope with very good optics. What's more, its build quality we found beyond reproach. Its only flaw is the narrow field of view of the zoom eyepiece you get in the box. Unfortunately it often happens with spotting scopes, especially if they feature a closed fixing system of eyepiece, one that doesn't allow to use the 1.25 inch standard. We think that, if producers already decide to go in that direction they at least should offer you 2-3 fixed-focus eyepieces apart from the zoom one. I think a 20-30× model with a field of view of 60-70 degrees should be obligatory as it is able to recompense an exeptionally narrow field offered by the zoom eyepiece at 20×. Vortex do feature such an eyepiece in their line-up but only with an in-build grid. The second eyepiece I would love to see as a part of the accessory kit is a 40-50× model with a field of 60-70 degrees. Contrary to smaller magnifications, at 60× the zoom eyepiece offers you the widest field of view, there is no need to complement it with another wide angle fixed-focal eyepiece. Still, it would be very welcome. Another wide angle prime eyepiece in the set could offer you a much better image than the zoom and its field would be a tad wider as well. In order not to duplicate the 60× magnification producers could add, for example, an 70-80× eyepiece which would allow to develop in full the potential of a good quality 85 mm objective lens with low dispersion glass. After all such magnification would come in handy for long-range uses during a sunny day and also it would allow you to admire the Moon, the brightest planets, binary stars, multiple-star systems, planetary nebulas , or globular clusters at night.