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During the past decade, 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, rainguard and 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 only 64mm.
Any binoculars of this size will show more when they are mounted using a tripod adaptor fixed to its integral mounting bush.
However these are light enough and the magnification is low enough to be held by hand 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 Triangulam 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
These binoculars really showed their potential when we took them to a dark rural site.
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 Triangulam 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.
The eye relief is stated as being 25mm.
This is measured from the rear surface of the eye lens, which is recessed into the eyepiece housing.
We measured the usable eye relief as 22mm, which we found to be more than sufficient to enable us to use the binoculars with glasses.
When we shone a bright light down the objective lens we saw that the reflective surfaces of the prisms were covered with what appeared to be black plastic covers.
This feature reduces the amount of stray light that can get into the optical system, where it can diminish image contrast.
The coating on the eyepieces and objective lenses has none of the tell-tale blotching that indicates shoddy workmanship.
It gives equal reflectivity all over the surface of each lens, suggesting that it has been evenly applied.
The lens surfaces only minimally reflect a bright white light, showing that the multicoating is effective.
The single rainguard type of eyepiece cover attaches to the neck strap for security, keeping it easily accessible.
Made from soft rubber, it protects the eyepieces from dew and debris when you are not actually using the binoculars, thereby reducing the frequency with which you will need to clean the eyepieces.
The neck strap is of far better quality than is usual
with this class of binoculars.
Although it is not padded, we found that the 30mm-wide webbing is sufficiently comfortable for the binoculars to be slung around the neck for over half an hour without digging in.
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This review originally appeared in the January 2014 issue of BBC Sky at Night Magazine.