A pair of 15×70 binoculars occupies a useful astronomical niche. When mounted they show more detail and depth than smaller handheld binoculars. They can also be handheld for short periods too. The Bresser Spezial Astro SF 15×70 binoculars are a new entrant to that niche.
The Spezial Astro SF 15x70s come in a rugged woven nylon case, with a padded neoprene neck strap, tethered objective lens caps, attachable rain guard-type eyepiece covers, microfibre cleaning cloth and an instruction leaflet.
The aluminium body is covered with a ribbed rubber armour and has a converter bush for a tripod adaptor (not included) at the objective end of the hinge.
The hinge moves smoothly, with enough resistance to prevent it from sagging when the binoculars are mounted, but not so much as to make it difficult to adjust.
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The individual eyepiece focusers are also smooth, but less stiff than the hinge, so you can focus the mounted binoculars without affecting the interpupillary distance (the distance between the pupils of your eyes).
The eyepieces can be folded down if you observe with spectacles, and you can see the entire field of view without pushing your glasses against the eyepieces.
Using a bright torch to examine the inside of the binoculars, we noted that the prisms are secured in proper cages and that the insides of the objective tubes are ribbed in order to reduce stray light and combat spurious reflections.
We tested the Spezial Astro SF 15x70s under good suburban skies, mounted on either a parallelogram mount or a monopod and trigger-grip, in addition to a few brief handheld excursions.
We found it easy to obtain a precise focus on our first target, a first quarter Moon. With either the terminator or the limb in the middle of the field of view, false colour was barely perceptible, and it was only at the periphery that it became obtrusive.
We did notice, however, that when the Moon was within about 10° of the target area, there was sufficient stray light to degrade the image.
Away from the Moon, we found there to be good image contrast and colour rendition. Albireo was conveniently placed and we found that its two components stars – one bright gold, the other dimmer blue – showed good colour contrast and were cleanly split almost to the edge of the field of view.
Despite its low elevation, we were able to detect the crescent of a rising Venus, and Jupiter’s glare at opposition was controlled well enough to enable us to see the Galilean moons close to the planet.
Where the Spezial Astro SF 15x70s really come into their own, however, is with deep-sky objects. You would expect the Andromeda Galaxy, M31, to be bright, and so it was.
The companion galaxies, M32 and M110, were obvious, as was the more abrupt light cut-off due to the dust lane on the nearer edge.
The much fainter galaxies that we tried, M33, M51 and M101, were all easily identified, even when the binoculars were handheld.
The North America Nebula, NGC 7000, required them to be mounted, when it too became obvious.
Testing the binoculars during the short summer nights meant that we had access to views of the southern Milky Way.
A particular delight was being able to directly compare the large clusters IC 4756 and NGC 6633 in the same field of view. Even the Ptolemy Cluster, M7, was visible as it skirted the southern horizon.
These successes tempted us to go on a dark nebula hunt in the constellation of Aquila. This too was fruitful: the ‘C’ part of Barnard’s E dark nebula, B142, was particularly easy to make out, which also revealed the sinuous curve of Barnard’s Black Lizard, B138, as it wove its way south from 23 Aquilae.
The manufacturer has obviously responded to observers’ calls for a no-nonsense pair of binoculars with useful features.
The Spezial Astro SF 15x70s will appeal to both the binocular observers and those with more experience who wish to step up from budget models.
Since the invention of the telescope, the cry of astronomers has been “more light!”. You want as much as possible of the light gathered by the objective lenses to be transmitted to your eyes.
The Spezial Astro SF 15x70s meet this requirement: there is none of the stopping down of the light cone that some binoculars use to reduce aberrations and sharpen the image, although there was a minuscule obstruction from a component in the prism cages.
This in turn requires that optical aberrations are well controlled. Except at the very edge, you will experience a flat field of view, with sharply focused stars and very little false colour.
Finally, where the light meets a glass surface, reflection must be minimised, something achieved with anti-reflective coatings.
Shining a torch into the lenses suggests that their glass-air surfaces all meet the “fully multi-coated” specification. This is a reassuringly bright pair of binoculars.
- Price £269
- Optics Fully multi-coated
- Aperture 70mm
- Magnification 15x
- Prisms Porro, BaK-4
- Angular field of view 4.4o
- Focusing Individual eyepiece
- Eye relief 20mm
- Interpupillary distance 56–74mm
- Weight 1.9kg
- Supplier Bresser UK
- Warranty 5 years
- Tel 01342 837098
This review originally appeared in the October 2020 issue of BBC Sky at Night Magazine.