Do you need six or more eyepieces to cover all aspects of astronomy? You might get away with just 3 plus a Barlow or can you manage with only one?

Zoom eyepieces have been around for a long time, most manufacturers have at least one in their range, but how good are they? Can they replace the three or four individual eyepieces their focal range covers and do they come up with the goods when it’s cold and dark?

Most spotting scopes we sell at Green Witch have a zoom eyepiece attached or one is purchased to go with the scope. It’s rare we sell a fixed focal length for terrestrial use except for a special purpose such as target shooting or photography. But zooms are available for astronomy as well so I decided to test a few.

Five zooms left the showroom with me for a night out with a William Optics 80mm f6.9 fluorite refractor mounted on an EQ5. The other equipment I used was a Williams Optics dielectric diagonal and a Williams Optics 2.5 apocromatic Barlow.

The five eyepieces I chose to test are: -

MAKE	PRICE	CODE	RANGE
OPTICAL VISION	49.99	OV-568	7-21mm
WILLIAM OPTICS	129.99	WO-E-ZOOM1	8-24mm
BAADER HYPERION	168.00	DH-2454824	8-24mm
TELE VUE	185.00	TV-CSZ-0824	8-24mm
MEADE	190.00	MEA-07199-2	8-24mm

William Optics

Baader Hyperion

Optical Vision

TeleVue (with optional astigmatism corrector installed)

Meade

The test was carried out on objects found in a March sky; daytime observation was also included for those of you that use your scope for bird watching or aircraft spotting. A four-day-old moon high in the sky during the day supplemented my test for the bird spotters.

The Moon during the day has low contrast, it was used to see how each eyepiece could reveal the subtlety of tone on the Lunar seas.

Distortion in an eyepiece reveals itself by bending straight objects at the edge of the field, a telegraph pole or a distant roof top will show how much.

Field curvature is the inability of an optical system to focus at the centre and edge of the field at the same time. Focus carefully on the Moon at the centre of the Field then move it to the edge then see if you have to refocus.

With all zoom eyepieces in this price range something has to be compromised. There is a degree of some of the above in all the eyepieces in this test. I had to look long and hard with some as they were almost perfect. Most astronomers will accept that perfection is only a goal and tolerate optical errors as long as don’t intrude too much. Apparent field of view with all zooms changes as the focal length is changed, being smaller at the longer end 24mm and wider at 8mm (for example 40°/24mm to 60°/8mm for William Optics. This seems the opposite to the ideal of low magnification/wide field (nebular/clusters) to high magnification/small field (planets). In fact the different magnifications mean you do get a wider field on the sky at the longer focal length; it is the apparent field that changes.

Testing was carried out by constant comparison, changing each over and over, it’s either better or not, can I or can’t I see it - it’s as simple as that. When something pops into view as it did with the TeleVue I go back to the others to see if I can detect it, usually you can see the object with a careful look, if it’s not obvious this makes the TeleVue a better eyepiece because it revealed more detail first time without any concentrated effort.

MAKE	Moon	M42	Trapezium	Saturn	Ease of Use	Value for Money	Total
OPTICAL VISION	5	7	8	7	6	12	45
WILLIAM OPTICS	8	8	10	10	9	10	55
BAADER HYPERION	9	9	8	6	9	9	50
TELE VUE	9	9	10	10	9	8	55
MEADE	9	9	9	9	9	7	52

The spread sheet shows how the eyepieces performed on each target, I gave each one a score out of 10 for each section. They all performed well, but the William Optics stands out, although not as good in some areas as others its ease of use and cost are major contributions to it’s success as was it’s planetary performance.

I was impressed with the quality of all the items tested; gone are the days of zooms being optically inferior or difficult to use. The optical Vision at £50 had its merits; if you want to have a go with a zoom try this one. I gave it 12 out of 10 because it’s such good value. It had no right to be tested in the company of the others, it was simply outclassed, the next one on the list actually cost over 2½ times as much.

The other four all have attributes that are desirable for any astronomer (or birder). The William Optics, TeleVue and Meade are all very sharp all the way from 24mm down to 8mm. The Meade gave a good high contrast view of M42 as did the TeleVue, the latter pipped it with critical sharpness but only just. The William Optics was lower in contrast and not as bright with the daylight observation of the moon but the view of the Orion Nebula M42 was very good. The four stars in the Trapezium shone like tiny diamonds and were separated at a very low magnification. The planetary performance of the TeleVue and William Optics was first class with the Meade just a tad behind. Saturn’s rings were crisp with the gap in between A and B seen in moments of good seeing.

The Hyperion is in a class of it’s own, it has a very wide field 50°/24mm to 68°/8mm. Not quite in the same league as the William Optics, TeleVue or the Meade in terms of resolution but not that far behind, it’s a perfect choice for Galaxy hunters or bird watchers.

In every test there has to be a winner and for me in this test it is the William Optics, scoring the same as the TeleVue but at a lower cost. A lottery win would see the TeleVue and Hyperion in my collection. The Meade unfortunately had the TeleVue at a lower cost to compete with although the difference between them is very small.

To Zoom or Not To Zoom, that was the question. The answer is a definite YES. Later you could add a longer focal length with a wide field of view and possibly a Barlow, then you will be totally covered for every observational need.

I have been surprised by the quality of the zooms tested and soon I would like to own my own. Those of you that know me will also know I am a planetary observer, so which one should I choose? Send me some feedback; I would like to hear your experience of zooms to help me decide.

* These are estimated

Ralph Bell
Green Witch, with writers cramp and a soon to be opened bottle of red!