FIRST LIGHT
Opticron Oregon Observation 11×70 binoculars
Great for deep-sky observing, but steer clear of bright, high-contrast targets
VITAL STATS
• Price £119
• Optics Multicoated
• Aperture 70mm
• Magnification 11x
• Prisms BAK4
• Angular field of view 4.6°
• Focusing Zeiss centre-focus
• Eye relief 25mm
• Interpupillary distance 57–73mm
• Weight 1.39kg
• Supplier Opticron
• www.opticron.co.uk
• Tel 01582 726522
During the past decade or so, inexpensive 70mm binoculars have become very popular among amateur astronomers. Given Opticron’s reputation for good quality, we were very keen to try its Oregon Observation 11x70s.
The binoculars came packaged with a soft and slightly padded nylon case, neck strap, lens caps and rain guard, plus a separate plastic wallet which held a microfibre cleaning cloth and the instruction booklet. The booklet is generic for several types of binoculars and is written in clear, standard English.
The binoculars have a slightly matt-finish rubber armour, which allowed us to grip confidently without having to hold on too tight. The hinge, focus wheel and right-eyepiece dioptre ring all moved smoothly with enough uniform resistance to make them easy to adjust but not liable to inadvertently slip. The minimum interpupillary distance is nominally 57mm, but this will be dependent on the width of the bridge of your nose.
When you hold the exit pupils up to the light, each appears perfectly round except for a single, almost imperceptible, ‘cut-off’ segment. This indicates slightly undersized prisms. The exit pupils of a pair of 11x70s should be 6.4mm in diameter, but we measured these as being just under 6mm. On investigation we found that, in common with most binoculars of this class, although the physical aperture is 70mm, the light path is internally stopped down to an effective aperture of 64mm.
Optical scrutiny
Any binoculars of this size will show more when they are mounted on a tripod with an adaptor fixed to its integral mounting bush. However, these are light enough and the magnification is low enough for them to be handheld for short periods. We focused the binoculars and found that the central third of the image was very crisp, but star images deteriorate noticeably outside this, showing coma and, near the periphery, astigmatism. Collimation was well within acceptable tolerances. There is a tiny amount of pincushion distortion; this removes the disconcerting illusion that the sky is the surface of a ball that appears to roll as you pan across it. All bright stars are surrounded by a faint halo, which is most probably due to light scatter inside the prisms. On-axis colour correction is good, but there is distinct chromatic aberration when you observe bright, high-contrast targets like the Moon or Venus even slightly off-axis.
Touring the deep sky
These binoculars are specified as being ‘multicoated’, which usually means that, unlike the objectives and eyepieces, the prisms are uncoated, resulting in intrusive ghost images when we observed the Moon. Apart from this, stray light is well controlled and we were unable to get spurious images from bright stars held just outside the field of view, indicating that the rudimentary baffling is adequate.
Bright Solar System objects are not the intended target of this sort of instrument so, once the Moon was out of the way, we looked farther afield. Our first target was the Andromeda Galaxy, M31: it filled the central ‘sweet spot’ of the field of view, where it showed a more abrupt cut-off in brightness at its northwestern edge, indicating the presence of the dust lane there. Our next target was the often difficult Triangulum Galaxy – in this case it was an easy spot under dark skies.
Next, we took a tour around the Milky Way. The Auriga clusters – M36, M37 and M38– were easy to distinguish from each other in size and brightness. The Dumbbell Nebula in Vulpecula was compact and bright with a rectangular appearance. Open cluster M39 in Cygnus can be difficult to distinguish from the background sky at higher magnifications, but in our test it was obvious, as were dark nebulae such as the Northern Coalsack. The double star Delta Cephei (separated by 22 arcseconds) showed clear dark space and beautiful colour contrast, while Herschel’s Garnet Star (Mu Cephei) was a stunning deep orange-red.
Overall, then, this is a very competent entry-level binocular for anybody who wants ultra-portable and wide-angle views of deep-sky objects.
Bright views of faint objects
When exit pupils of an optical instrument match the size of your own pupils, you get the brightest possible image. Unfortunately, this also means you see the full effect of any light pollution. Heading to a rural site where the sky background is dark allowed us to make the most of the 6mm exit pupils these binoculars offer – granting us much brighter views of faint, large objects such as the North America Nebula, the Triangulum Galaxy and the Pinwheel Galaxy than we could see under suburban skies.
We also noted a subtle improvement in the already good colour rendition of stars and this, coupled with the exquisitely clean split into its yellow and blue components, made Albireo (Beta Cygni) particularly beautiful. Combined with the ease of holding them reasonably steady by hand, this dark-sky potential makes the Oregon Observation 11x70s an ideal pair of binoculars to take on stargazing trips away from city lights.
KIT TO ADD
1. Slik Pro 400DX three-section tripod
2. Slik SH-707SP tripod panhead
3. Opticron Pro Series lens cleaning cloth in pouch
VERDICT
