Fujinon TechnoStabi review
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Neil Bone appraises Fujinons stabilised wonder.
For many years the standard advice to beginners in astronomy has been that binoculars offer the ideal first serious instrument.
Although it is now possible to obtain good quality first telescopes, a good pair of binoculars is, however, still the best place to start in many areas such as deep sky or comet observing. Some of the best views of comet Hale-Bopp in the spring of 1997, for example, were through wide-field, low power binoculars.Sweeping the rich summer Milky Way for nebulae and clusters is a pleasure with binoculars and there are hundreds of variable stars whose magnetic changes are best covered using binoculars.

Binoculars have the great advantage of compactness and portability. Even a small telescope requires some setting up, whereas with binoculars, they are ready to use as soon as the lens caps are off.

Hand held binoculars can be pointed rapidly to any part of the sky. The downside, of course, is that the image is often unsteady: there are limits to how long even the most muscular arms can hold a pair of binoculars in front of the eyes before the weight leads to shaking. One solution is to prop the elbows on a wall or other convenient rest. Another is to mount the binoculars on a tripod. The latter option obviously defeats the principle of portability by adding to the equipment which has to be transported to the observing site, while the former may not prove possible at a given location.

The last couple of years have seen the appearance on the market of binoculars which, at least in large part, get round these problems. The Fujinon Techno-Stabi image-stabilised binoculars are certainly an interesting addition to the range.


Magnification and aperture
Binoculars, as most amateur astonomers know, are described in terms of their magnification and aperture. For instance, a pair described as 10x50 have a magnification of x10, and each objective (front end) lens has an aperture of 50mm.

An important consideration for astonomical use is the 'exit pupil', the diameter of the cone of light emerging at the eyepiece end. This is found by dividing the aperture by the magnification, so for a pair of 10x50s, the exit pupil is 5mm in diameter. Ideally, to deliver the brightest image, the exit pupil should be similar in diameter to the dilated pupil of the observer's dark-adapted eye. Typically this is of the order of 5-7mm, so that 10x50s are ideal for most people: younger observers, whose pupils dilate more fully, may benefit from using 7x50s with a 7mm exit pupil.

The Fujinon Techno-Stabi binoculars are rated at 14x40, offering an exit pupil of 2.86mm. Most 40mm binoculars come as 7x40, but the manufacturers manual suggests that the stabilisation improves performance sufficiently to justify the higher magnification.

The multi-coated optics of the Fujinon Techno-Stabi binoculars are mounted in a sealed, dry nitrogen purged unit. The bincoulars offer a four degree field of view, and the image-stabilisation hardware brings their weight up to a chunky 1.3kg.

Image stabilisation is achieved using a gimbal assembly, containing erecting prisms in the light train. Sensors detect horizontal and vertical motions, which are corrected for via motors on the assembly.
The whole system is controlled by a microprocessor. Image stabilisation requires power from four AA batteries, with a working lifetime of three hours.

Testing the binoculars.
I put the Techno-Stabi binoculars through their paces on a couple of clear nights in early February, alongside my tried-and-trusted standard 10x50s which have been in service for 24 years.

The first session was on a night somewhat affected by patchy cloud and haze. Jupiter and Saturn, high in the evening sky, provided an ideal starting point.

Obviously, a magnification of x14 is too low to reveal any detail on the planets themselves, but I was interested to see how well the binoculars would perform in revealing Jupitors four main, Galilean satellites. The answer was: very well! I was unable to pick these out with my 10x50s in the conditions, but the image-stabilised binoculars showed all four, in line, immediately - three to the east, and one to the west of Jupiter.
Saturn showed a markedly elliptical image, though the rings themselves were, hardly surprisingly, not resolved at x14 magnification.

Low in the southeast, Sirius provided a good test for star images. This appeared perfectly sharp with no spikes, fringes or other optical defects apparent, with the 14x40s. Focusing, using the small knob on the binoculars' right-hand side was smooth and easy. Image stabilisation is operated using easy-to-press buttons on top of the unit.

The image stabilisation really came into its own for picking out star clusters. I found I was able to look comfortably at the Pleiades, high in the southern sky, for a couple of minutes at a time without the distraction of image shake. The views of other winter clusters, including the trio of M36, M37 ad M38 in Auriga, the Perseus Double Cluster, Praesepe (M44) and M67 in Cancer, M35 in Gemini and M41 in Canis Major were all excellent.

Moving from object to object with the image stabilisation on was at first curious. Having grown used, over many years, to the natural jerky motion of hand-held binoculars, the 'gliding' sensation given by the image stabilisation was a pleasant suprise.

One relatively minor drawback I found was with the status light at the binoculars' eyepiece end - green for stabilisation on, orange for standby. This is an obvious problem for observers trying to preserve night vision. I learned fairly quickly to position my thumb over the light while observing. In routine use, I guess a longer-term solution would be to cover the light with tape.

A later very clear, frosty night allowed some more exacting tests. Early in the evening, I again turned the Techno-Stabi binoculars on Jupiter, to check whether stabilisation really made a difference to the satellites' visibility. Not having checked beforehand, I had no idea of what configuration the satellites would be in. A first look, without stabilisation, showed one satellite on its own, well to the east of Jupiter with, possibly, two close together to the west. As soon as I switched the stabilisation on, the possible twosome became three sharply resolved points of light. Later consultation of the BAA Handbook confirmed that Io, Callisto and Europa were closely grouped at the time of observation. Unquestionably, image stabilisation improves the binoculars' resolving power in hand-held operation.

The improved resolution also has advantages for variable star observing. For some stars, particularly near the faint end of the binocular visibility range, making accurate estimates can be difficult when the variable and/or comparisons are close to other field stars. Such has been the case for the cataclysmic variable CH Cygni during its recent comparatively faint spell; making estimates in my 10x50s has required care of late. With the Fujinons in stabilised mode, however, estimating CH Cyg's brightness was easy, even with the field low in the north-western sky.



Elsewhere, in the field for Mira, I was able to pick out comparison Y (mag. +8.82) easily from the BAA chart sequence, even with the Moon fairly nearby.

The Moon itself was a pleasing target, a five-day crescent on this evening. There was still a hint of earthshine showing up the unilluminated portion. The image-stabilised 14x40s allowed me to make out the profiles of the dark Mare Ibrium and Oceanus Procellarum on the unlit side. Meanwhile, there was plenty to be seen along the terminator (day-night line), as this cut across the cratered southern lunar highlands.

The 100km diameter crater Theophilus was outstanding, its 10km wide central peak clearly snapping into view when the stabilisation was switched on. I have had worse views of the Moon through small telescopes.
Later in the night, after moonset, I went in search of some tricky deep sky objects. The ninth-magnitude galaxy M65 in Leo was a good test. At best, this was only glimpsed in my 10x50s even though the sky was very transparent (naked eye limiting magnitude better than +6) and Leo well up in the southeast. In the 14x40s, without stabilisation, M65 was a lot easier. I put this down to the comparitively darker sky background and greater contrast resulting from the Fujinons' smaller exit pupil. Stabilisation made little difference to the view.

Similar results were found with the easier M51 - the Whirlpool Galaxy - in Canes Venatici. The main advantage with the image stabilisation on was undoubtedly the ease with which the binoculars could be held on target - viewing was positively comfortable!

Whilst stabilisation made little difference for galaxies, it did work wonders for viewing what I have always found a difficult binocular Messier object, the small mag. +8 nebula M78 north of Orion's Belt. Even under these good conditions, I could only barely glimpse M78 in the 10x50s. It was, however, clearly visible in the 14x40s, especially with image stabilisation on.

Finally, the globular cluster M3 in Canes Venatici was very fine indeed in the Fujinons with image stabilisation on.


Astronomical Binoculars?
A useful power-saving feature of the binoculars is that they will switch to standby if left for about a minute. This worked well, even in the cold conditions of this February night. The binoculars do, indeed, live up to the manufacturer's claim that the stabilisation hardware justifies the higher-than-normal magnification for a 40mm aperture instrument.

Can the Techno-Stabi binoculars be recommended for astonomical use? I would say they can, especially for variable star observing. The x14 magnification allows pleasing views of deep sky objects and is fine for casual observation of the Moon. I can imagine these binoculars being handy for taking on overseas trips where weight is a limitation: the image-stabilisation all but removes the need for a tripod.


Neil Bone is a Contributing Consultant to Astronomy Now. His trusty 10x50 binoculars have been used to make more than 11,000 variable start estimates since 1976.

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