Focal Length: 3.5mm, 5mm, 7mm, 10mm, 14mm
Supplier: Tring Astronomy Centre
Telephone: 01442 822997
Gone are the days when all celestial observations had to be made through a ‘porthole’ view – manufacturers are now keen to deliver the immersive sensation achieved through the use of wide-field eyepieces.
Although Vixen already produces an eyepiece collection with a 65° apparent field of view, their new SSW eyepieces increase this substantially to 83°.
This new collection comprises oculars with focal lengths of 3.5mm, 5mm, 7mm, 10mm and 14mm, with the shorter focal lengths favouring Solar System objects and galaxies, and longer ones open clusters and extended nebulae.
The SSW eyepieces incorporate a fully multicoated, seven-element design using high-transmission, low-dispersion glass – including Lanthanum and other special glasses – housed in a compact body.
The eyepieces have 1.25-inch chrome finish barrels and a beautifully non-reflective black internal finish that includes a 28.5mm thread for standard filters.
What will really catch your eye is the anodised alloy band that colour codes each eyepiece to help you tell them apart, although we found this to be of limited use in the dark.
As well as the colour coding, each focal length is clearly marked in white on the coloured band.
On removing the top dust cap an elegant twist-up rubber eyecup is revealed.
In its fully retracted position it is just under 5mm above the 26mm diameter eye lens, but it affords 7.5mm of maximum extension.
Some spectacle wearers will be disappointed to know that we were unable to see the whole field of view while wearing glasses, as the eye relief of approximately 13mm was insufficient to allow our eyes to get close enough to the lens even with the eyecup fully retracted.
Even without glasses, we had to adjust our eye placement very carefully to see the edges of the enormous field of view.
Exploring the skies
When swapping eyepieces it is always a bonus if they are parfocal with one another and the Vixen SSWs didn’t disappoint here with ±160µm maximum variance.
This makes it very easy to switch from one focal length to another without needing to adjust the focus very much.
We tested the eyepieces in our own 10-inch Sky-Watcher Dobsonian and our grab-and-go William Optics Megrez 72 refractor, which have focal ratios of f/4.7 and f/6 respectively.
The views were excellent through both instruments, with very good neutral colour control on both daytime and celestial objects.
Examining the lunar limb with the 3.5mm, 5mm and 7mm eyepieces showed little sign of glare or unwanted reflections.
There was a glorious two-day-old Moon at the start of one of our observing sessions and the contrast between the earthshine and the bright crescent made for a wonderful sight through the 10mm eyepiece.
M45, the Pleiades star cluster in Taurus, was well placed during the review period and made for a fine view, the 10mm and 14mm eyepieces revealing excellent contrast between the bright member stars and the dark background of the sky.
It was here that we felt the ‘immersion’ effect of a wide field of view most, finally closed off by a well-defined field stop.
Later in our observing sessions M42, the Orion Nebula, was high in the sky and we spent a long time tracing out the wealth of detail visible in the extensive fine tendrils of the nebulosity at various magnifications.
This was followed by close scrutiny of the Trapezium region using the 3.5mm and 5mm eyepieces.
Star testing using Aldebaran in Taurus showed crisp, clean shapes to over 90 per cent of the field of view with some spikiness becoming apparent towards the very edge of the field, especially in the 5mm eyepiece, indicating a tiny amount of astigmatism.
Extraneous light from objects close to but outside the field of view was hardly discernible.
The Vixen SSW eyepieces produce excellent views and their build quality is beyond reproach, making them an excellent choice for intermediate to advanced observers, but beginners may struggle with eye placement.
A field of view so deep you could get lost
The new Vixen SSW eyepieces are all about producing a wide field of view.
As well as focal length, eyepieces are selected for their ‘apparent’ field of view in degrees.
The apparent field of view is the angular diameter of the circle of light received by your eye when looking through an eyepiece.
However, this is not the true field of view that you will observe through a telescope as that is dependent on magnification.
Magnification is calculated by dividing the telescope focal length by the eyepiece focal length.
The true field of view can then be found by dividing the apparent field of view by the magnification.
A wide field of view provides an immersive observing experience, making the observer feel more part of what they are seeing.
Typical eyepieces supplied with telescopes have an apparent field of view of 50° so the 83° field of view of the SSW eyepieces is a huge increase – so much so that we had to work quite hard to discern the edge of the view.
Each eyepiece has two coloured, anodised alloy bands around the body, the larger of which is 14mm deep.
The colours are arranged in wavelength order: shorter wavelengths (towards purple) correspond to shorter focal lengths and longer wavelengths (towards red) correspond to longer focal lengths.
The eyepieces have 1.25-inch barrels with a well applied chrome finish.
The barrels have lightly machined undercuts to stop the eyepieces falling out of the focuser if the retaining bolt loosens in use.
These worked well in both our Baader Steeltrack and William Optics eyepiece holders, with no sign of snagging.
The rubber grip on each eyepiece is the same as that on Vixen’s SLV eyepiece range and has a clever hexagonal profile that prevents the eyepieces from rolling if placed on their sides.
This profile also gives the eyepiece a reasonably solid grip surface when picking it up.
Multicoating the lens elements increases light transmission, with Vixen claiming 99.5 per cent transmission for the SSW eyepieces.
The coatings were applied to a very high standard with no blemishes and displayed a mainly green tinge with hints of purple deeper into the eyepiece body.
Soft rubber twist-up eyecups are fitted to each eyepiece and these were a joy to use as their action was smooth, solid and easily adjustable.
We found that eye positioning was quite critical to optimise the wide field of view and these comfortable eyecups made this easy to achieve.
This review originally appeared in the May 2016 issue of BBC Sky at Night Magazine.