Alula tests top birding scopes, part II: Do small
scopes deliver?

In ALULA 1/2002, we tested the elite ‘full-sized’ telescopes with 77–85 mm objectives. This time we test the small scopes which can be expected to come closest to the performance of the big ones: Nikon 60 mm Fieldscope ED III A, Swarovski’s new ATS 65 HD, and the Zeiss Diascope 65 T* FL. It would also be justifiable to include in this group Kowa’s TSN 663 ED, which I reviewed in ALULA 4/2001. However, during that test the quality of the eyepieces available for it—especially the zooms—proved to be so disappointing that I decided to omit it this time. We tested the scopes primarily with zoom eyepieces, but I have added to the discussion of each scope my own brief assessment of the quality of the wide-angle eyepieces available. 

Our team performed the field test outdoors at a nature reserve in Helsinki on a cloudy and slightly foggy day in December when the temperature was several degrees below 0°C. In addition, I checked the optical quality of the scopes indoors using resolution targets and gathered some field experience with them on my own over a period of time: these results were chiefly used to verify the results our team acquired during the field test, check the reliability of the manufacturers’ field of view specifications, and evaluate the low-light performance of the scopes. 

Small vs. Large: what do you get and what do you have to give up? 

There are two main reasons why a buyer might opt for a smaller scope over a bigger one: to get a lighter and more easy-to-carry package, and hopefully pay less as well. As for their weights (combined weight of the scope and its zoom eyepiece), the scopes in this test are some 330–350 g lighter than the corresponding full-size scopes by the same manufacturers. This may not appear much, but my experience is that these small scopes also tolerate lightweight video heads and tripods (such as Manfrotto 128/055) better than the larger scopes, making the scope/tripod combination more stable and/or lighter. With Nikon and Zeiss, the size differences are also not that great with a circa 5 cm difference in length compared to their ‘big brothers’, but in the case of the Swarovski—due to the length of the AT 80—the difference is about 10 cm. Zeiss and Nikon have about a 25–30% price difference between their small and large scopes, but Swarovski’s new small scope and its zoom costs more or less the same as the older 80 mm model. Thus, these small scopes cannot be considered real bargains. 

A special tripod system was used in order to make a comparison of the scopeviews easier. The picture shows the Nikon and Swarovski.

 

If smaller scopes were indeed as good as the bigger ones, birders would not be carrying the latter save for a few individuals who wanted to stand out from the crowd. However, inescapable laws of physics dictate that at equal magnifications a larger aperture objective gives a brighter, more contrasting, and, a surprise to many birders, a higher resolution image than a smaller objective. This, of course, is providing that the optics are otherwise of equal quality. Or to put it another way: a larger objective enables higher magnifications. We received our trio of small scopes at the same time as the group of full-size scopes we tested in ALULA 1/2002, and, therefore, tried them out in the field side-by-side. As the full-sized scopes proved to provide significantly higher performances, I ended up carrying out resolution distance comparisons with small and large scopes. In these tests, I measured the distance at which a certain fixed resolution target is still just barely resolvable at a given magnification with each scope, where the result is influenced by the optics’ sharpness, brightness, and contrast. In these tests—just as optical theory predicts—the measured distances corresponded quite closely with the ratio of objective lens diameters of the different scopes. Thus, with an 80 mm scope, for example, one could expect to just barely be able to identify a bird at a distance 1.23x farther than with a 65 mm scope. What surprised me about these tests was that this difference was already apparent at 20x and remained more or less constant throughout the range of magnifications and at different light levels (including very bright daylight). A diagram of these results (drawn from actual measurements with two scopes) accidentally slipped into the ALULA 1/2002 telescope test without any explanation, for which the editors of ALULA apologise. 

Are special lens materials worth the price? 

Zeiss Diascopes are only available with an objective lens made of fluoride glass, but both Nikon and Swarovski offer less-expensive versions of the ED- and HD-scopes tested here, where the only difference is that their objectives are conventional achromatic lenses. Briefly put, the difference is that with special glasses the various colours of the spectrum are brought to common focus much better, whereas with achromatic objectives the blue-purple end of the spectrum, in particular, remains slightly out of focus when yellow-green and red are in focus. Especially at high magnifications, this is visible as purple or yellow-green fringing around high-contrast objects, and the colours are also not as vivid or bright. In low light, the differences become more pronounced and special glasses yield significantly better contrast. With respect to resolution, however, achromatic objectives can be almost as good as objectives made of special glasses. Scopes with ED-, HD- and fluoride objectives tend to cost about 50% more than those with achromatic objectives. 

Again the issue of quality control 

Individual variations in quality influence a scope’s resolution—even to the extent that an excellent specimen of a small scope can, despite the facts explained above—resolve just as well as a mediocre specimen of a larger scope. Among the scopes tested here and in ALULA 1/2002, four units exhibited optical defects that noticeably compromised their performance at high magnifications. I later obtained other units for testing, and their performance also varied to the extent that the relative ranking, with respect to resolution and contrast of the models, depended on the particular units tested. Since I found such variations in all of the manufacturer’s scopes, I have reluctantly decided to leave open the question that is perhaps the most interesting for the reader, namely which of the tested scopes has the best optics. 

Nikon Fieldscope ED III A and 20-60x zoom MC 

The Fieldscope ED III A is a high-resolution small scope that is easy to bring to a sharp focus even at high magnifications. Nikon’s colour rendition has a slight reddish bias, the contrast is very good, and brightness a bit below Zeiss and Swarovski. Viewing against the sun, the Nikon exhibits very little flaring. The field of view with a zoom (2.0–0.96°) is typical, that is, narrow and tunnel-like, image quality near the edge is good and the image is easy on the eye, but finding the optimum eye position is rather critical. 
The rubber-covered eyecup is of the twist-up type, and eye-relief with the zoom is on the short side for those who wear glasses: those who view through their glasses should try this out before buying. The compact metal body has rubber armouring on the prism housing and a retractable lens hood. With the zoom eyepiece, the scope weighs c. 1.3 kg and is c. 33.5 cm long. The designers have placed the tripod foot in front of the large, rubber focus ring, thereby making the scope annoyingly rear-heavy. The press-on objective lens cap stays on well and does not break easily. The eyepiece cap is also of the press-on type and is deep enough, but as it is a bit too loose it could easily be lost. The scope lacks a usable aiming device, and since the eyepiece is offset from the scope’s centre line, aiming takes more practice than in the other two. You may need to add a ‘cable-tie-sight’ (as explained in ALULA 1/1997) or a similar device. Focusing is too fast and so stiff that image shake during focusing is unavoidable. The zoom action, in contrast, is smooth and light. The threaded eyepiece mount is solid and well sealed. The small Fieldscope is waterproof and nitrogen purged and comes with a ten-year warranty and a carrying case, which unfortunately has to be removed for viewing. The Fieldscope ED III A also takes Nikon’s excellent 24x, 30x, 40x, and 60x MC wide-angle eyepieces. 

3Swarovski ATS 65 HD and 20-60x zoom S 

Swarovski’s latest offering features sleek and modern styling, which drew praise from most that saw it. The body is completely armoured with the green synthetic rubber that characterises Swarovski’s binoculars, and the new, large zoom eyepiece merges almost seamlessly into the body. For a small scope, the Swarovski offers a high-resolution image that is bright, highly contrasting, easy on the eye, and very even throughout the zoom’s range. Viewing against the sun, it exhibits very little flaring. The colour balance has a slight warm golden-yellowish bias. The field of view of the zoom eyepiece is somewhat wider than customary at 2.06–1.14°, although it comes nowhere near that of the Zeiss at lower magnifications. However, the image is noticeably less tunnel-like than is customary with zooms, and the quality at the edge of the field is excellent at all magnifications. Finding optimum eye placement is relatively easy, but not quite as instinctive as with the older zoom of the 80 mm Swarovski. The eyepiece has a comfortable, broad-rimmed rubber twist-out eyecup, and eye-relief is also sufficient for viewing with most spectacles. With the zoom eyepiece, the scope is 36 cm long (a little longer than the Nikon) and weighs 1.37 kg. Like the Nikon, the Swarovski is also irritatingly rear-heavy. The scope’s design makes aiming along the scope body very difficult, so Swarovski has designed a small removable tube-sight which sits adjacent to the eyepiece, and which our test team did not find particularly helpful. A more successful innovation, on the other hand, is that the eyepiece cap is tethered to the eyepiece by a short cord, thereby preventing it from getting lost. However, on windy days the free-dangling cap might be annoying. The objective lens cap fastens with a bayonet and is slightly more solid than most, but it was such a tight fit that putting it on was not easy. There is a wide rubber ring around the body for focusing. It is geared very well, being neither too slow nor too fast, but is so stiff that image shake during focusing is unavoidable. The wide rubber zoom ring offers a good grip, but is likewise very stiff. The eyepiece mount is a sturdy bayonet with a safety latch preventing accidental removal. The Swarovski is waterproof and nitrogen filled (the eyepieces are also waterproof) and comes with a ten-year warranty. As the scope is fully armoured, no protective case is offered. In addition to the zoom, two new wide-angles (20x and 30x) are available, and a 45x wide-angle is reportedly to follow in late 2002. I also briefly tested the wide-angles, both of which give a 66° subjective field and ample eye-relief for those who use glasses. Their field of view is not quite as wide as in Nikon’s and Zeiss’ wide-angles, but the 30x, especially, gave otherwise absolutely superb performance. Its image is very even, easy on the eye, and sharp to the very edge of the field, and very much resembles the image of Leica’s excellent 32x wide-angle. The 20x gives significantly poorer quality at the edge of the field, but in other respects it is also excellent. 

3Zeiss Diascope 65 T* FL and 15-45x Zoom3 

 

Save for its smaller objective with a shorter focal length, the 65 mm Zeiss is identical to the 85 T* FL and uses the same eyepieces. Thus, it provides smaller magnifications than the other two scopes under review here. Given that with these small scopes the distance from which a given target can be resolved improves by only about 10% when the magnification is increased from 45x to 60x, one might well think that the much wider field of view the Zeiss provides at 15x offsets its lack of high magnifications. The 65’s field of view is 3.2–1.5°, meaning that at 15x magnification it covers an area 2.4 times larger than the scope in the test with the next widest field (Swarovski ATS 65) at 20x. The Zeiss image is sharp and bright. The contrast is good but not quite on a par with the Nikon and Swarovski, and the colour balance has a marked yellowish-green bias, which renders it less neutral than the other two. Viewing against the sun, the Zeiss also exhibited more flaring than the others. The wide field of the Zeiss zoom lens means that the image does not feel narrow and constricted in the manner we have come to expect with zooms. However, a relatively broad area of the field edge has rather poor image quality, especially at low magnifications, where the edges appear acceptably sharp only if you place your eye closer to the eyepiece than is optimal for easy viewing of the centre of the field. Starting with about 30x magnification, the edges begin to look quite good, although even with high magnifications the Zeiss’s edge quality is distinctly below that offered by the Swarovski zoom. In birding, however, a wide field of view, even if the image is soft at the edges, is much more useful than a narrow one which is sharp to the edge. When panning, the image of the Zeiss bends and twists unpleasantly, but one would probably get used to this in time. Finding optimum eye position and acquiring the best image was easy. The eyecup is made of thick rubber. It pulls out and twists to lock in place, but on the cold testing day was very reluctant to move. Eye-relief is sufficient for viewing with most spectacles. The focusing system is a Leica-like double knob with separate knobs for fast and fine focusing. The system works very well as the knobs are well spaced, and you can grip the fine-focus knob between your thumb and forefinger, making focusing easy, precise, and shake-free. The fast-focus knob is unpleasantly stiff. Zooming was smooth but unnecessarily stiff, and the zoom’s grip is not rubber. The eyepiece mount is an exceptionally rugged and well-sealed bayonet. The silver-coloured metal body has thick rubber armour under the prism housing, and the retractable lens hood is also rubber-covered. The objective lens cover is a flimsy bayonet-fastened plastic plate, the use of which requires nimble fingers. In contrast, the eyepiece cover is a solid and thick rubber cup, which is a little too tight. A groove on the lens hood assists aiming. This device works reasonably well, but using it requires moving one’s head quite far from the viewing position. Zeiss scopes have a ten-year warranty. In addition to the zoom, 23x and 30x wide-angles are also available. I tried these briefly and found them very good, providing a bright and sharp image, but they were not quite as easy on the eye and had poorer edge resolution than Nikon’s and Swarovski’s wide-angles. With its zoom, the Diascope 65 FL weighs 1.43 kg and is 36 cm long. Zeiss’s small scope is also rear-heavy, but less so than the Nikon and Swarovski. 

Conclusions 

The performance of this trio was quite even, and I find myself unable to give an absolute recommendation for the best choice. However, for those who wish to have magnifications above 45x the Swarovski might prove better as it has a slightly larger objective than the Nikon and because its zoom eyepiece provides a wider field, is better suited to spectacle wearers, and has somewhat better resolution at the edge of field. Nikon, in turn, is slightly more compact and has a broader selection of wide-angle eyepieces. Zeiss offers better handling than the other two and its field of view is far superior, but as it does not reach equally high magnifications, you may encounter situations where you cannot identify a bird your could have identified at a higher magnification with the other scopes. 

The separation capacity of large and small scopes. The scale shows from which distance certain details can be seen with c. 80 mm and c. 65 mm scopes. Suurennos x = Magnification x.

 

 

Kimmo Absetz