Test of Various Eyepieces with Helios Quantum-7.4 25×100 Observation Binocular

Test of Various Eyepieces with Helios Quantum-7.4 25×100 Observation Binocular

Helios Quantum-7.4 Observation Binocular 25x100

Helios Quantum-7.4 Observation Binocular 25×100

On my way back from visiting my son at the uni, I popped in to see a customer who asked me to try couple of eyepieces with his Helios Quantum-7.4 Observation Binocular. It is a high quality binocular with 25x magnification and 100mm aperture, specially designed for astronomical observations, although it can be very well used for terrestrial observations, too.
Like most telescopes, this observation binocular came supplied with a pair of 25mm eyepieces of mediocre quality. The idea was to replace it with a pair of zoom or fixed focal length eyepieces to achieve much better viewing experience. During the test we saw that it is possible and when we compared it to the very similar Japanese binocular that the customer also possessed, we saw very little difference, so a pair of high quality eyepieces can make a huge difference, especially if we take it into account that the above mentioned Japanese binocular did cost more than twice the price of the Helios Quantum-7.4 including the cost of the replacement eyepieces.

Another aim of the this test was to find a pair of shorter focal length eyepieces for higher magnification views, but without compromise to the quality of view.

List of eyepieces tested:
25mm stock eyepiece (supplied with binocular) | Angular Field of View: ?°  | Eye relief: ?
15mm GSO Plossl Eyepiece | Angular Field of View: 52°  | Eye relief: ?
SkyWatcher 8-24mm Zoom Eyepiece (1.25″/31.7mm) | Angular Field of View: 40° – 60° | Eye relief: 15mm – 18mm
Celestron Zoom Eyepiece 1.25 in – 8-24mm | Angular Field of View: 40° – 60° | Eye relief: 15mm – 18mm
SkyWatcher ExtraFlat Wide-Angle 27mm 1.25-inch Eyepiece | Angular Field of View: 53° | Eye relief: 23mm
Baader Hyperion Eyepiece 21mm | Angular Field of View: 68° | Eye relief: 20mm
12.5mm Japanese Abbe Orthoscopic Eyepiece (not available anymore, high definition alternative replaced it)
9mm Japanese Abbe Orthoscopic Eyepiece | Angular Field of View: appr. 45° | Eye relief: ?
5mm Japanese Abbe Orthoscopic Eyepiece (not available anymore, high definition alternative replaced it)


Celestron Zoom Eyepiece 1.25 in - 8-24mm

Celestron Zoom Eyepiece 1.25 in – 8-24mm

We started with a pair of 8-24mm zoom eyepieces. These are being sold under various brands by Skywatcher, Celestron and others. We have tried the Skywatcher and Celestron versions.
The Skywatcher version looks exactly the same as the Celestron, but without brand name on it and the Celestron seem to have a much stronger green optical coating. Optically there isn’t much difference between them, although the Celestron 8-24mm Zoom eyepiece provided slightly brighter, crisper image than the Skywatcher version. This is most likely due to the different, higher quality optical coatings applied to the optical elements in the case of the Celestron 8-24mm Zoom Eyepiece. The only drawback with these zoom eyepieces is the compromise with field of view, so we moved onto fixed focal length eyepieces.

The pair of 15 mm GSO Plossl eyepieces provided a nice, clear view, but not as sharp as with other, fixed focal length eyepieces like the original 25 mm stock eyepieces that came with the binocular or the 27 mm Skywatcher Flatfield Wide View eyepieces. We assumed that this slight loss of sharpness was most likely due to the nearly twice as high magnification…

Then we compared the 25 mm stock eyepieces (that came with the binocular) with a Skywatcher 27mm Flat Field Wide Angle eyepieces. The view through the stock eyepieces was not sharp at the edges, the field of view was narrow and some strange reflections were visible. Please note that we were pointing the binocular at a very distant multi-level building with lots of lights on it as it was dark outside. This was a good environment to test the quality of the anti-reflection coatings of the various eyepieces as well. Through the Skywatcher 27mm Flat Field eyepiece the was was much more enjoyable with wider field, much less reflections and with sharp to the edge image.

Baader Hyperion Eyepiece 21mm

Baader Hyperion Eyepiece 21mm

Then we decided to try a pair of Baader Hyperion 21mm eyepieces. The body of this eyepiece is much bigger than any other eyepiece that we had on test, so it was slightly more difficult to keep the eye in the correct position than in the case of the 27mm Flat Field eyepieces, but we benefited from much wider field of view. Not surprisingly, the field was not as flat as in the case of the 27mm Flat Field eyepiece and there was marginally more chromatic aberration visible. In the end the customer purchased a pair of Skywatcher 27mm Flat Field eyepieces, although personally I preferred the view through the Hyperion, despite the slightly more chromatic aberration. To be honest this is quite personal and it’s difficult to compare two eyepieces of different focal length as the view will always be so different at different magnifications…

We didn’t expect much from trying shorter focal length eyepieces, but we still did test the binocular with few Abbe Japanese Orthoscopic eyepieces. The 12.5mm Ortho provided surprisingly good, sharp image and when we further increased magnification by going for the 9mm Ortho, the image was darker, but still bright enough and sharp, however when we replaced them with 5mm Ortho eyepieces the view became so dark that it became very difficult to focus. Although this series of Orthoscopic eyepieces have been discontinued as the Japanese manufacturer retired (it was a small private company), we still have few of the 9mm orthos in stock and once these are sold, we’ll start importing a new series of even higher quality HD Orthoscopic eyepieces, also made in Japan. We expect the results will be very similar, or marginally better.


SkyWatcher ExtraFlat Wide-Angle 27mm 1.25-inch Eyepiece

SkyWatcher ExtraFlat Wide-Angle 27mm 1.25-inch Eyepiece

The best visual results were provided by the 27mm Skywatcher Flat Field eyepiece and the 21mm Baader Hyperion eyepiece. We expect that other Hyperion eyepieces, like the 24mm Hyperion or the 31mm Hyperion Aspheric would give very similar or even better results than the 21mm Hyperion due to lower magnification. The 68 degree field of the Hyperion gave a very enjoyable wide field of view.
If higher magnification is desirable, orthoscopic eyepieces could be considered as good alternatives but not below 9mm focal length. A 12.5mm orthoscopic eyepiece would be the best compromise for high magnification views.

Baader Hyperion 8-24 mm Clickstop Zoom Eyepiece 1.25

Baader Hyperion 8-24 mm Clickstop Zoom Eyepiece 1.25″ MARK III

If the user is happy to sacrifice field of view for the comfort of quick change of magnification by a use of a pair of zoom eyepieces, a Celestron 8-24mm Zoom eyepiece would be a good start and definitely better than other similar, but cheaper 8-24mm zoom eyepieces. We have not tested, but we would expect that a pair of the new Celestron Deluxe 8-24mm Zoom eyepieces or the Hyperion 8-24mm Zoom eyepieces would be the best solution if price is not an issue, as from past experience we know that the Hyperion 8-24mm Zoom eyepiece is a favorite upgrade to replace the stock eyepiece of Celestron Ultima Spotting Scopes.

Article by Zoltan Trenovszki


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Posted on June 15th, 2014.