The eyepiece market is booming. Every other month, a new line of oculars hit the shelves promising better eye relief, field of view or some other desirable feature. Zoom eyepieces – which offer a range of magnifications in one neat package – have also followed this trend, with a raft of new models available to the discriminating observer. But not all zooms are created equal, as you’ll discover by using them in the field.
Earlier zooms were blacklisted by many observers owing to their inferior performance compared with eyepieces offering a fixed focal length. They complained of decreased sharpness, loss of light and questionable mechanical construction among other things. But recently a new line of zooms promising much improved performance over their predecessors has helped to buck that trend. One such product is the Mark III Baader 8-24mm Hyperion zoom, which I was eager to put through its paces.
The Baader Hyperion zoom arrived well packaged inside a sturdy cardboard box, which included a soft leather pouch to store the eyepiece and a variety of adapters that allow you to use the zoom in either 125 inch or 2-inch mode. All the adapters are threaded for filter attachment. The package also includes an alternative rubber eyecup with a raised shade to block off stray light. No written instructions are provided with the product, although the box very clearly illustrates the way all the accessories relate to each other. I elected to order up the dedicated 2.25x Barlow lens with the eyepiece in order to coax a larger range of magnifications from the eyepiece. At the time of writing, retailers offer both as a package at a slightly reduced price compared with buying each item separately.
The zoom is a seven element, fully multicoated design and possesses click stops at 24, 20, 16, 12 and 8mm settings. The motions are smooth and the field of view ‘opens out’ as one dials in the shorter focal lengths from 50 degrees at the 24mm setting to 68 degrees at the 8mm setting. What’s more, the eyepiece is continuously variable, allowing you to get additional magnifications between the click stop settings. The eye cup can also be adjusted in height so as to make viewing the entire field as comfortable as possible. Eye relief is a generous 12-15mm, enabling those who wear eyeglasses to make use of the zoom. Overall, the Baader zoom has the look and feel of a quality product but how did it square up under actual use? To answer this question, I tested the eyepiece on a 80mm f/5 short tube achromatic refractor as well as a 180mm f/15 Maksutov Cassegrain.
Notes from the field
The Mark III Hyperion zoom worked well when coupled to the fast achromatic refractor. Images were clean and bright with good colour fidelity and sharpness across most of the field of view. The field stop at the 24 and 20mm settings looked a bit soft compared to that observed at the higher power settings. Testing on a flat roof a couple of hundred yards distant, showed excellent sharpness and contrast. Some pincushion distortion was noted in the outer 10 per cent of the field at the 24mm setting (17x) but was noticeably improved when greater magnifications were dialled in. Although a little bit on the heavy side, the Baader zoom would make an excellent eyepiece for spotting ‘scope enthusiasts. Indeed, when coupled to the short tube 80 it makes for a good quality 17-50x spotting ‘scope, thus providing a decent range of magnifications for terrestrial use. The various adapters accompanying the zoom will also allow you to couple it to a DSLR for daylight photography. When coupled to the dedicated 2.25x, I could extend the magnification range on the 80mm f/5 to 113x, a nice upper limit for a rich field telescope. No significant deterioration in the image was noted using the Barlow.
The majority of my tests were carried out on celestial targets and once again the Hyperion zoom did not disappoint. In the fast achromatic refractor, stars focused down to tiny pinpoints and remained sharp over most of the telescopic field. Only the outer 15 per cent or so could I see significant distortion at the 24mm setting. Increasing the magnifications improved the edge of field performance quite a lot. Indeed at 50x (the 8mm setting), stars remained crisp and sharp nearly to the edge of the field. Unlike other zooms I have experienced, there was no sign of lateral colour. I consider this a very satisfactory result for such a fast telescope.
When I switched to the 180mm Maksutov, the performance of the Baader zoom was noticeably better. Stars resolved to tiny round Airy disks across the entire field of view under good conditions. No sign of ghosting was seen at any magnification indicating that the proprietary phantom anti-reflection coatings were working effectively.
The eyepiece is not parfocal between click stops. A considerable amount of refocusing is necessary when switching between the high power (8mm) and low power ( 24mm) settings of the eyepiece.
The traditional drawbacks of zoom eyepieces are best revealed when they are compared with high quality, fixed focal length oculars. In this capacity, I compared a good quality 20mm Plossl in the 180mm Maksutov to the view obtained using the 20mm setting of the zoom. My target was the bright star Vega and its hinterland. Switching between eyepieces the views were more similar than they were different. The fixed focal length Plossl showed slightly less scatter and the sky was just a shade darker but I was genuinely impressed by how well the zoom eyepiece held its own in comparison.
In praise of ergonomics
The Baader Hyperion zoom is an excellent value in today’s market, offering versatile optical performance satisfyingly close to fixed focal length oculars. It is incredibly handy for finding celestial objects at lower powers and then one can dial in the right amount of magnification that best frames the target. Fumbling about in the dark interchanging eyepieces will become a thing of the past and that in itself is a worthy reason for using it. Highly recommended!
Dr. Neil English’s latest book, Grab ‘n’ Go Astronomy, has just been published by Springer.