Svbony SV215 3-8mm planetary zoom

[Zermelo]

Purchase

I ordered my zoom directly from Svbony, at a cost of £105.91, plus £20.92 for shipping and taxes. This was the “duty fully paid” price, though you can choose to skip the taxes and settle up when it arrives (or not, according to your luck).
I pre-ordered and it took about four weeks, arriving in time to be a Christmas present. Some filthy weather followed, delaying my chance to test it out. When it did clear, there was a succession of very cold nights, and I tried it out on eight occasions during January.

 

Observing Location

All sessions were conducted at the same, semi-rural, mid-Bortle 4 location.
The darkest SQM reading was 20.75, when the moon was absent.

 

Observing Conditions

The temperature over the eight sessions ranged from 6°C down to -4°C.
The moon phase ranged between 0% and 91%, but several of the sessions coincided with nights lacking a moon.
Relative humidity ranged from 56% to 86% (no obvious dew was observed during any session).
Seeing varied from Antoniadi IV to II; where significant, specific conditions are mentioned below.
Transparency varied from 4/7 to 6/7; a persistent hazard in the cold weather was smoke from nearby houses in specific directions.

 

OTAs Used

One session used a 150mm F/5 Newtonian, two sessions a 102mm F/5.9 achromat, and five with a 127mm Maksutov, approx. F/12. Where a specific OTA is not mentioned for an observation, the Mak is indicated by default.

While the slower focal ratio of the Mak tends to reduce differences in performance between eyepieces, it does have the advantage of introducing fewer aberrations of its own, compared with, for example, the CA in the achromat and coma in the Newtonian.

 

Comparison Eyepieces

The following eyepieces were used in comparison observations, some more than others:

Baader Morpheus 9mm
BST Starguider 8mm
OVL Hyperflex zoom 7.2mm-21.5mm (used at 7.2mm)
ES 82° series 6.7mm
Baader Morpheus 6.5mm
BCO 6mm
BST Starguider 5mm
BCO 10mm + x2 multiplier (hence 5mm equivalent)
OVL Nirvana-ES 4mm

Of these, the BCO 10mm is probably the sharpest on-axis.

 

Other Equipment

Baader semi-APO filter
Astronomik UHC filter

The refractor was used with a 2” quartz/dielectric mirror diagonal. The Mak was equipped with a 1.25” Takahashi prism.

With its short focal lengths, the zoom will mostly be used unenhanced, but a brief test was conducted with an Altair x2 telecentric multiplier.

 

The Observer …

… is as important as the other components in the optical train. So, for the guidance of the reader:

Experience: I have completed around 150 observing sessions, including 1800+ observations. I have so far seen 100 Messier objects and split doubles down to 0.9”.

Corporeal status: my eyeballs are the wrong side of fifty years old. In my Bortle 4 skies, I can’t see much beyond +5 NELM.
My observing eye (when examined 18 months ago) has astigmatism of -0.75 cyl. I’m not aware of any other defects.

 

Results

 

I couldn’t decide whether to order the comments by target object or by defect type, and ended up doing a bit of both.

 

Physical Attributes

 

The eyepiece is compact, and quite heavy for its size. It looks and feels solid. The rotating zoom action is smooth and easy to operate, though the final step from 4mm to 3mm requires a little more torque, since the leverage is increased. By comparison, I found it easier to adjust than my Hyperflex 7.2-21.5mm. Zooming in cause the eye lens to rise on a central stalk, in the same way as the Televue Nagler zoom.

The click stops are obvious without being overly severe. It was easy to keep track of the focal length in the dark by counting the stops from either end of the range. There was no noticeable stiffening of the mechanism in sub-zero conditions. In each of the three OTAs the eyepiece was held in different compression rings, and with moderate tightening it was easy to hold the eyepiece firmly enough that it did not slip when the zoom level was changed. I did not notice any change in the resistance through a session, nor any over the three weeks since I’ve been using it in anger.

As has been noted in other reviews, the nosepiece is rather long, and would have impacted on the prism in the Tak diagonal. I installed a single parfocal ring to prevent this; it also has the effect of moving the zoom ring away from the diagonal, allowing easier access with gloved fingers. Other reviewers have recommended the parfocal ring to allow both hands to be used, one holding the ring while the other operates the zoom. I did not find this to be necessary, but it is possible.

The rubber eyecap is neither too sloppy when extended, nor too difficult to fold back. The eye lens is recessed only by a small amount.

It was noticeable that there was only just enough inward travel on the Newtonian to achieve focus, although this would have been less pronounced without the parfocal ring and the helical focuser used in the scope.

 

Observations: Stray Light Control

The main use of this eyepiece for me will be for higher magnification viewing of planets, the moon and tight multiple stars, and also possibly planetary nebulae and globular clusters. For planets and brighter/tighter double stars in particular, stray light (scatter/ghosting) will be detrimental.

A word or two about “ghosting”. This term seems to be used by different people to refer to differing optical defects. For the avoidance of doubt, the usage in the descriptions below means a phenomenon where – almost always when a very bright object is being viewed – there is a near-uniform disc superimposed on the image, ranging in brightness from barely perceptible to quite detrimental, and of a size that is variable, but may fill the entire field (and then may be detected by an overall reduction in contrast). I was going to mock up a simulation, then I found this one in CN:

 

[EDIT:  to be clear, the artefact above that I am identifying as ghosting is the circular area with a reasonably clear edge, which is not concentric with the planet. The image also shows scatter, which shows here as a larger, more diffuse area, with no obvious edge. In my observations, it was not always true that the scatter area was larger than the ghosting, if both were present, but the appearance of both was like those in this mock up]

If the eye is moved in one direction, the artefact moves in the opposite direction. Since the cause is unwanted reflections from surfaces that may include the observer’s own eye, the effect can also be a little ephemeral.

The most relevant observations for assessing stray light were the planets and brighter double stars, though tighter faint doubles and the moon were also useful. I suspect that individual observations to assess stray light were sometimes affected by meteorological factors, which is why I wanted to perform a number over different evenings.

 

Solar System

Saturn had become inaccessible from the observing site since Christmas. Jupiter was observed on three occasions, though it was not well placed, quite low down and above rooftops. On two of the three, the conditions were so poor that the views were worthless, in any eyepiece, but the other observation (with the Mak 127) was in decent (Antoniadi II) seeing.

At 8mm (x188), the Svbony showed a strong NEB and SEB, and two fainter belts closer to the poles. The NEB showed some fine detail to its northern edge. The Galilean moons were tight, and each had a sharp diffraction ring. Ganymede showed a slightly creamy colour, when compared with the others. Some ghosting was seen, though not so much that it ruined the scene. The view in the 8mm BST was very similar. Both eyepieces showed a little more scatter around the Jovian disc than the Morpheus 9mm, though the background sky was not as dark in the Morpheus.

Mars was much better placed with respect to altitude during the review period. With the Mak 127 in good (Antoniadi II) seeing across three sessions, the Svbony consistently showed a distinct North polar cap and obvious, but less clear, darker markings. The edge of the disc was sharp through 6mm>5mm>4mm (x250 > x375), though scatter increased and so did ghosting. However, at 6mm it showed better detail than the Morpheus 6.5mm and ES 6.7mm, although the Morpheus showed a little less scatter, which improved the contrast with the adjacent sky. At 4mm, the Svbony had more ghosting than the Nirvana 4mm, but less scatter and a sharper disc. At 3mm, the Svbony image revealed no new detail (unsurprising at x500)

In more mediocre conditions, the Svbony at 8mm showed albedo features when the BST 8mm did not (both showed the North Polar cap). The disc edge was also sharper in the Svbony, and remained so through to 6mm, delivering pleasing views. The image in the BCO 6mm was similar, but with some ghosting.

Uranus was observed once in moderate (III) seeing, showing a good disc in the Svbony at 5mm, with a nice, obvious green colour. At 4mm there was a little scatter, but less than the Nirvana 4mm, and the Nirvana image was noticeably dimmer.

A Baader semi-APO filter was tried briefly for Mars and Jupiter with the Svbony and other eyepieces, on the refractor and on the Mak. It killed the violet fringe on the achromat, in all eyepieces, though it wasn’t very obvious in the first place. With the Mak, of course, there was no fringe, but the semi-APO has a Neodymium substrate that might have enhanced planetary features. There was no noticeable improvement, for any eyepiece, so most of the observations were conducted without.

The moon was observed in a single session, using the 150mm Newtonian, in a waxing gibbous phase (approximately 10.4 days old). While there was significant jet stream activity overhead, the seeing was good, and the target was at an altitude of approximately 60°. No filter was used.

At 8mm and 7mm, the Svbony views were very crisp. Craters and mountains near the terminator showed much detail, especially the terraces of Copernicus, and the surrounding features. The colour of the smoother areas seemed neutral and natural. The Morpheus 6.5mm showed as much detail, and of course with a wider field, though it did show some pronounced yellow/brown chromatic aberration of the exit pupil near the field stop; I’ve experienced this effect with the Morpheus only on Luna.

Taking the Svbony up to 5mm (x150) did not diminish the sharpness, or the overall satisfaction of the view. At least 20 craterlets were visible in Clavius. The BST 5mm was not quite as sharp, though the eye relief was better, and the view out to the field stop was more easily taken in. When the eyecup was screwed up to avoid blacking out, the experience was more comfortable than the Svbony at this focal length.

At 4mm (x188), the Svbony view was still sharp and pleasant, though showing no more detail than before. The 4mm Nirvana showed as much, but there seemed to be an obvious yellow cast across the field, and also some CAEP like the Morpheus. Maxing out the Svbony at 3mm (x250) made the lack of any extra detail visible as image softening, though it did not otherwise break down.

 

Brighter Stars (including multiple stars)

In difficult (Antoniadi IV) seeing, the Svbony at 5mm (x300) gave a slightly better view of Rigel than the BCO 10mm + x2 multiplier, though the companion was unseen with either. Castor showed little scatter in the Svbony at 7mm (x214), and the contrast with the surrounding sky was good. At 4mm, the view was very slightly crisper and brighter than in the Nirvana 4mm, though both were unavoidably unsteady.

In good (II) seeing in a different session, the Svbony at 7mm and 6mm showed a lovely split of Castor with sharp diff. rings, though the contrast was affected by some pronounced ghosting. A further observation at 4mm in the refractor (x150) showed little scatter or ghosting, resulting in a sharp, contrasty view. The 4mm Nirvana gave a largely similar view, though stronger ghosting reduced the sky contrast, and the diffraction rings were not quite as crisp. Rigel’s companion was also seen in better conditions with the Svbony at 7mm in the Mak, sharp between the fourth and fifth rings.

In moderate (III) seeing in the Mak, the Svbony at 6mm showed a vibrant view of Almach, though with a fair bit of scatter from the primary. The Morpheus 6.5mm was very similar, but with a little more ghosting. The ES 6.7mm image was as sharp, but had higher levels of scatter and the colours were washed out to some extent. In similar conditions, Algieba was neatly split by the Svbony at 6mm (x250). Again, the views in the Morpheus 6.5mm and ES 6.7mm were similar, but with a touch more scatter in the latter. In better (II) conditions with Almach, the Svbony at 8mm (x188) delivered a very bright, pleasant view, with well-coloured stars, neat diffraction rings and good contrast against the background sky, in spite of some scatter. The Hyperflex zoom at a similar magnification produced a near-identical view (it should really get more use than it does). At 6mm the Svbony image was still pleasing, as sharp as the BCO 6mm, but with less scatter.

In poor (IV) seeing, Alnitak (2.1”) showed identically in the Svbony at 5mm and in the equivalent BCO 10mm + Altair x2 combination, the companion seen in the second diff. ring in still moments.

 

Tighter and/or Fainter Multiple Stars

Most eyepieces will handle stray light better with dimmer targets. Across the sessions there were several observations of multiple stars where magnitude was less of a challenge.

In difficult seeing with the Mak, the Svbony at 5mm split 36 Andromedae (+5.5, +6.5, 1.2”) in stiller moments, as did the 5mm BST, although the latter view had the inferior contrast. At 4mm the Svbony still showed little scatter, while the 4mm Nirvana had noticeably more scatter, though also splitting the pair occasionally.

In challenging seeing (IV), three components of σ Orionis (+3.8 AB, +8.8 C, +6.6 D, +6.3 E, seps. 29.9” down to 11.6”) were visible in the Svbony at 8mm. Increasing to 4mm (x375) was sufficient to show the fourth component (C) in occasional quiet moments and, while hardly comfortable, showed a little less scatter than the Nirvana. In slightly better seeing (III), the Svbony at 7mm showed the C component a little more clearly than the Morpheus 6.5mm on one occasion, but the honours were reversed on a different evening. At 5mm, the view in the Svbony was very similar to the BCO 10mm with the x2 Altair telecentric multiplier.

η Orionis (+3.4, +4.9, 1.8”) showed its companion to the Svbony at 5mm, sitting in the diff. ring. The BCO 10mm + Altair x2 combination was similar, possibly a shade superior on scatter.

32 Eridani (+4.7, +5.9, 6.9”) in poor (IV) seeing showed less scatter and better contrast in the Svbony at 5mm, compared with the BCO 10mm + Altair x2, and also showed more of a colour distinction, though this was better still in the Morpheus 9mm.

λ Orionis (+3.4, +5.5, 4.5”) was seen as well in the Svbony at 7mm as in the ES 6.7mm, and the diff. rings appeared crisper at 5mm (x300).

HR 1902 (+5.7, +6.6, 1.2”) was just split in difficult conditions with the Svbony at 4mm (x375), an easier job than with the Nirvana 4mm, which gave more scatter.

6 Trianguli (+5.2, +6.7, 3.7”) was pleasant in the Svbony at 5mm (x300) in good (II) seeing. The BST 5mm gave noticeably more scatter. At 4mm the discs were not as tight and scatter increased, but still a touch better than the Nirvana.

γ Arietis (+3.9, +4.6, 7.4”) in good (II) seeing was beautiful in the Svbony at 6mm (x250), with little scatter and two sharp diff. rings on each star. The BCO 6mm was equally sharp, but increased scatter affected the contrast with the background sky.

ε Arietis (+4.6, +5.6, 1.3”) in moderate (III) seeing, was just about split in the BCO 6mm, with very little scatter. The Svbony at 6mm (x250) showed almost no scatter, and delivered a view with more contrast, brighter and crisper. The split was wider at 5mm, with similar image quality. Increasing to 4mm and 3mm resulted in more scatter and larger discs, but still not unpleasant. The same target on a poorer evening (IV) was just split in the Svbony at 6mm, but still showed very little scatter and good sky contrast. In the Morpheus 6.5mm the view was very similar.

Tegmine (+5.6 AB, +6.3 C, 5.9”, and +5.3 A, +6.2 B, 1.2”) in good (II) seeing, with the Svbony at 8mm, showed a very slight yellow/blue distinction, with little scatter. At 6mm AB was resolved with no degradation of quality. The Morpheus 6.5mm was very similar, possibly having slightly tighter stars. At 4mm (x375), the Svbony effected a split of AB, with some increase in scatter. The view was considerably better than that shown by the Nirvana, where any AB split was masked by stronger scatter.  

Achird (+3.4, +7.5, 13.6”) in good (II) seeing with the Svbony at 5mm (x120 in the refractor) showed the faint secondary clearly, and a sharp primary with a couple of diff. rings, though there was some ghosting. The Morpheus 6.5mm was a fraction crisper, but the ghosting was stronger.

In addition to the regular observations, when I observed Almach in the Mak, I moved it to just beyond the edge of the field stop. When exiting the field, the star was extinguished rapidly, and only a little light was seen to leak into the view with it placed just outside the stop, commensurate with the levels of scatter I’d seen in other observations.

 

Contrast

This has already been mentioned in several of the preceding observations. When targeting doubles, reduced scatter and/or ghosting can enhance the contrast with the background sky, an aesthetic improvement, but also useful where fainter companions are to be detected. For Mars/Jupiter/Saturn, contrast can make the difference between seeing a feature or not.

In addition to the comments so far, there was one observation of a planetary nebula:

NGC 2392 (Clown Face/Eskimo nebula) in the Svbony at 8mm was very obvious and extended, though no specific structure detected, with good contrast and with the central star seen with direct vision. At 6mm, brightness was reduced and averted vision needed, though this was also true of the Morpheus 6.5mm. The addition of an Astronomik UHC filter did not obviously enhance the view.

 

Field Curvature

This is a tricky one to assess. Firstly, observers can accommodate differential focus to different extents, and younger eyes can generally manage better – they may not even detect that the field is not flat. Also, FC is affected by the rest of the equipment, and the net effect is often an interplay between eyepiece and OTA. Perversely, an eyepiece with strong FC may seem excellent if used in an OTA imparting an opposite curvature.

In mitigation of the first point, my eyes are not the most youthful, and I don’t think much will be hidden on that account. On the second point, I have used three OTAs of different designs and focal lengths, and the Mak, at least, ought to be showing the picture reasonably accurately.

As I will be using the zoom with a driven mount, and mostly on compact targets, FC isn’t my top concern, but I did a little investigation.

In the Mak 127, Almach was allowed to drift to the edge and no defocusing was observed.

In the F/5 Newtonian, 36 Andromedae was focused in the centre of the field with the Svbony at 4mm, and gradually moved to the edge. Some refocusing was required from about 75% from the centre, but still gave a decent image. Beyond around 85%, the stars developed aberrations that could not be refocused. Given the results in the Mak, I ascribe the reflector observations to FC and coma in the OTA, rather than the eyepiece.

 

Barlowing

The zoom is unlikely to be used with a Barlow, but one test was conducted with a 2x Altair telecentric multiplier at 8mm, comparing the view with the zoom at a native 4mm. There was no discernible difference.

 

Blacking out

I have previously been pulled up on the distinction between this effect and “kidney beaning”, the latter being apparently very rare in the modern eyepiece. Blacking out, then, is restricted to the phenomenon where there is a comparatively small range of distances between the eye and eye lens that show the image properly, so that correct positioning of the eye becomes critical. This can be helped by a suitable eyecup, comfortable seating, etc.

In none of the observations so far have I noticed this effect with the Svbony, though I did see it a couple of times with the BST 5mm and Morpheus 6.5mm.

 

Eye relief

This was the most obvious drawback of the Svbony. At 6mm – 8mm it was adequate, but hardly comfortable. At shorter lengths, folding back the eyepiece was essential to access the full field, and then care was needed not to touch the eye lens (one session did result in a deposit from eyelashes).

I don’t need to wear eye glasses to observe, but I got the impression that it would be difficult or impossible.

 

Parfocality

As others have reported, the Svbony is not parfocal. Whether or not “nearly parfocal” is a meaningful attribute is moot (and very much so on CN). I found that the slightest touch of refocusing was needed on the longer focal lengths, and a little more at the short end. Other eyes may find that less is required.

 

Conclusions

In modest scopes, for most of the time, the Svbony held its own against fixed eyepieces ranging from the decent budget end to upper-mid-price.

For its most likely use cases, it controlled stray light acceptably well and delivered sharp, engaging views with decent contrast. Over the review period, on average, it outperformed the Nirvana 4mm, BCO 6mm, and BST Starguiders. It probably won and lost to the ES 6.7mm in equal measure, and was outperformed clearly only by the Morpheus.

It does not, of course, have a field as wide as some of the comparison fixed eyepieces, so the experience is inevitably diminished to that extent. The main disadvantage is its tight eye relief, particularly at the shorter end, which makes it less comfortable to use than some of the fixed eyepieces.

The Svbony zoom is a capable eyepiece and, at the price, should make a mark. With its 3mm-8mm range and small form factor, it could usefully be paired in a travel case with a longer zoom such as the Hyperflex 7.2mm-21.5mm.
I’m happy to have taken a chance on it.

 

 

Edited February 20, 2023 by Zermelo
Further clarification of stray light aberrations shown in image

[Second Time Around]

A truly excellent review!  More please.

[bosun21]

31 minutes ago, Zermelo said:

Purchase

 

I ordered my zoom directly from Svbony, at a cost of £105.91, plus £20.92 for shipping and taxes. This was the “duty fully paid” price, though you can choose to skip the taxes and settle up when it arrives (or not, according to your luck).
I pre-ordered and it took about four weeks, arriving in time to be a Christmas present. Some filthy weather followed, delaying my chance to test it out. When it did clear, there was a succession of very cold nights, and I tried it out on eight occasions during January.

 

 

Observing Location

 

All sessions were conducted at the same, semi-rural, mid-Bortle 4 location.
The darkest SQM reading was 20.75, when the moon was absent.

 

 

Observing Conditions

 

The temperature over the eight sessions ranged from 6°C down to -4°C.
The moon phase ranged between 0% and 91%, but several of the sessions coincided with nights lacking a moon.
Relative humidity ranged from 56% to 86% (no obvious dew was observed during any session).
Seeing varied from Antoniadi IV to II; where significant, specific conditions are mentioned below.
Transparency varied from 4/7 to 6/7; a persistent hazard in the cold weather was smoke from nearby houses in specific directions.

 

 

OTAs Used

 

One session used a 150mm F/5 Newtonian, two sessions a 102mm F/5.9 achromat, and five with a 127mm Maksutov, approx. F/12. Where a specific OTA is not mentioned for an observation, the Mak is indicated by default.

 

While the slower focal ratio of the Mak tends to reduce differences in performance between eyepieces, it does have the advantage of introducing fewer aberrations of its own, compared with, for example, the CA in the achromat and coma in the Newtonian.

 

 

Comparison Eyepieces

 

The following eyepieces were used in comparison observations, some more than others:

 

Baader Morpheus 9mm
BST Starguider 8mm
OVL Hyperflex zoom 7.2mm-21.5mm (used at 7.2mm)
ES 82° series 6.7mm
Baader Morpheus 6.5mm
BCO 6mm
BST Starguider 5mm
BCO 10mm + x2 multiplier (hence 5mm equivalent)
OVL Nirvana-ES 4mm

 

Of these, the BCO 10mm is probably the sharpest on-axis.

 

 

Other Equipment

 

Baader semi-APO filter
Astronomik UHC filter

 

The refractor was used with a 2” quartz/dielectric mirror diagonal. The Mak was equipped with a 1.25” Takahashi prism.

 

With its short focal lengths, the zoom will mostly be used unenhanced, but a brief test was conducted with an Altair x2 telecentric multiplier.

 

 

The Observer …

 

… is as important as the other components in the optical train. So, for the guidance of the reader:

 

Experience: I have completed around 150 observing sessions, including 1800+ observations. I have so far seen 100 Messier objects and split doubles down to 0.9”.

 

Corporeal status: my eyeballs are the wrong side of fifty years old. In my Bortle 4 skies, I can’t see much beyond +5 NELM.
My observing eye (when examined 18 months ago) has astigmatism of -0.75 cyl. I’m not aware of any other defects.

 

 

Results

 

I couldn’t decide whether to order the comments by target object or by defect type, and ended up doing a bit of both.

 

 

Physical Attributes

 

The eyepiece is compact, and quite heavy for its size. It looks and feels solid. The rotating zoom action is smooth and easy to operate, though the final step from 4mm to 3mm requires a little more torque, since the leverage is increased. By comparison, I found it easier to adjust than my Hyperflex 7.2-21.5mm. Zooming in cause the eye lens to rise on a central stalk, in the same way as the Televue Nagler zoom.

 

The click stops are obvious without being overly severe. It was easy to keep track of the focal length in the dark by counting the stops from either end of the range. There was no noticeable stiffening of the mechanism in sub-zero conditions. In each of the three OTAs the eyepiece was held in different compression rings, and with moderate tightening it was easy to hold the eyepiece firmly enough that it did not slip when the zoom level was changed. I did not notice any change in the resistance through a session, nor any over the three weeks since I’ve been using it in anger.

 

As has been noted in other reviews, the nosepiece is rather long, and would have impacted on the prism in the Tak diagonal. I installed a single parfocal ring to prevent this; it also has the effect of moving the zoom ring away from the diagonal, allowing easier access with gloved fingers. Other reviewers have recommended the parfocal ring to allow both hands to be used, one holding the ring while the other operates the zoom. I did not find this to be necessary, but it is possible.

 

The rubber eyecap is neither too sloppy when extended, nor too difficult to fold back. The eye lens is recessed only by a small amount.

 

It was noticeable that there was only just enough inward travel on the Newtonian to achieve focus, although this would have been less pronounced without the parfocal ring and the helical focuser used in the scope.

 

 

Observations: Stray Light Control

 

The main use of this eyepiece for me will be for higher magnification viewing of planets, the moon and tight multiple stars, and also possibly planetary nebulae and globular clusters. For planets and brighter/tighter double stars in particular, stray light (scatter/ghosting) will be detrimental.

 

A word or two about “ghosting”. This term seems to be used by different people to refer to differing optical defects. For the avoidance of doubt, the usage in the descriptions below means a phenomenon where – almost always when a very bright object is being viewed – there is a near-uniform disc superimposed on the image, ranging in brightness from barely perceptible to quite detrimental, and of a size that is variable, but may fill the entire field (and then may be detected by an overall reduction in contrast). I was going to mock up a simulation, then I found this one in CN:

 

 

If the eye is moved in one direction, the artefact moves in the opposite direction. Since the cause is unwanted reflections from surfaces that may include the observer’s own eye, the effect can also be a little ephemeral.

 

The most relevant observations for assessing stray light were the planets and brighter double stars, though tighter faint doubles and the moon were also useful. I suspect that individual observations to assess stray light were sometimes affected by meteorological factors, which is why I wanted to perform a number over different evenings.

 

Solar System

 

Saturn had become inaccessible from the observing site since Christmas. Jupiter was observed on three occasions, though it was not well placed, quite low down and above rooftops. On two of the three, the conditions were so poor that the views were worthless, in any eyepiece, but the other observation (with the Mak 127) was in decent (Antoniadi II) seeing.

 

At 8mm (x188), the Svbony showed a strong NEB and SEB, and two fainter belts closer to the poles. The NEB showed some fine detail to its northern edge. The Galilean moons were tight, and each had a sharp diffraction ring. Ganymede showed a slightly creamy colour, when compared with the others. Some ghosting was seen, though not so much that it ruined the scene. The view in the 8mm BST was very similar. Both eyepieces showed a little more scatter around the Jovian disc than the Morpheus 9mm, though the background sky was not as dark in the Morpheus.

 

Mars was much better placed with respect to altitude during the review period. With the Mak 127 in good (Antoniadi II) seeing across three sessions, the Svbony consistently showed a distinct North polar cap and obvious, but less clear, darker markings. The edge of the disc was sharp through 6mm>5mm>4mm (x250 > x375), though scatter increased and so did ghosting. However, at 6mm it showed better detail than the Morpheus 6.5mm and ES 6.7mm, although the Morpheus showed a little less scatter, which improved the contrast with the adjacent sky. At 4mm, the Svbony had more ghosting than the Nirvana 4mm, but less scatter and a sharper disc. At 3mm, the Svbony image revealed no new detail (unsurprising at x500)

 

In more mediocre conditions, the Svbony at 8mm showed albedo features when the BST 8mm did not (both showed the North Polar cap). The disc edge was also sharper in the Svbony, and remained so through to 6mm, delivering pleasing views. The image in the BCO 6mm was similar, but with some ghosting.

 

Uranus was observed once in moderate (III) seeing, showing a good disc in the Svbony at 5mm, with a nice, obvious green colour. At 4mm there was a little scatter, but less than the Nirvana 4mm, and the Nirvana image was noticeably dimmer.

 

A Baader semi-APO filter was tried briefly for Mars and Jupiter with the Svbony and other eyepieces, on the refractor and on the Mak. It killed the violet fringe on the achromat, in all eyepieces, though it wasn’t very obvious in the first place. With the Mak, of course, there was no fringe, but the semi-APO has a Neodymium substrate that might have enhanced planetary features. There was no noticeable improvement, for any eyepiece, so most of the observations were conducted without.

 

The moon was observed in a single session, using the 150mm Newtonian, in a waxing gibbous phase (approximately 10.4 days old). While there was significant jet stream activity overhead, the seeing was good, and the target was at an altitude of approximately 60°. No filter was used.

 

At 8mm and 7mm, the Svbony views were very crisp. Craters and mountains near the terminator showed much detail, especially the terraces of Copernicus, and the surrounding features. The colour of the smoother areas seemed neutral and natural. The Morpheus 6.5mm showed as much detail, and of course with a wider field, though it did show some pronounced yellow/brown chromatic aberration of the exit pupil near the field stop; I’ve experienced this effect with the Morpheus only on Luna.

 

Taking the Svbony up to 5mm (x150) did not diminish the sharpness, or the overall satisfaction of the view. At least 20 craterlets were visible in Clavius. The BST 5mm was not quite as sharp, though the eye relief was better, and the view out to the field stop was more easily taken in. When the eyecup was screwed up to avoid blacking out, the experience was more comfortable than the Svbony at this focal length.

 

At 4mm (x188), the Svbony view was still sharp and pleasant, though showing no more detail than before. The 4mm Nirvana showed as much, but there seemed to be an obvious yellow cast across the field, and also some CAEP like the Morpheus. Maxing out the Svbony at 3mm (x250) made the lack of any extra detail visible as image softening, though it did not otherwise break down.

 

Brighter Stars (including multiple stars)

 

In difficult (Antoniadi IV) seeing, the Svbony at 5mm (x300) gave a slightly better view of Rigel than the BCO 10mm + x2 multiplier, though the companion was unseen with either. Castor showed little scatter in the Svbony at 7mm (x214), and the contrast with the surrounding sky was good. At 4mm, the view was very slightly crisper and brighter than in the Nirvana 4mm, though both were unavoidably unsteady.

 

In good (II) seeing in a different session, the Svbony at 7mm and 6mm showed a lovely split of Castor with sharp diff. rings, though the contrast was affected by some pronounced ghosting. A further observation at 4mm in the refractor (x150) showed little scatter or ghosting, resulting in a sharp, contrasty view. The 4mm Nirvana gave a largely similar view, though stronger ghosting reduced the sky contrast, and the diffraction rings were not quite as crisp. Rigel’s companion was also seen in better conditions with the Svbony at 7mm in the Mak, sharp between the fourth and fifth rings.

 

In moderate (III) seeing in the Mak, the Svbony at 6mm showed a vibrant view of Almach, though with a fair bit of scatter from the primary. The Morpheus 6.5mm was very similar, but with a little more ghosting. The ES 6.7mm image was as sharp, but had higher levels of scatter and the colours were washed out to some extent. In similar conditions, Algieba was neatly split by the Svbony at 6mm (x250). Again, the views in the Morpheus 6.5mm and ES 6.7mm were similar, but with a touch more scatter in the latter. In better (II) conditions with Almach, the Svbony at 8mm (x188) delivered a very bright, pleasant view, with well-coloured stars, neat diffraction rings and good contrast against the background sky, in spite of some scatter. The Hyperflex zoom at a similar magnification produced a near-identical view (it should really get more use than it does). At 6mm the Svbony image was still pleasing, as sharp as the BCO 6mm, but with less scatter.

 

In poor (IV) seeing, Alnitak (2.1”) showed identically in the Svbony at 5mm and in the equivalent BCO 10mm + Altair x2 combination, the companion seen in the second diff. ring in still moments.

 

Tighter and/or Fainter Multiple Stars

 

Most eyepieces will handle stray light better with dimmer targets. Across the sessions there were several observations of multiple stars where magnitude was less of a challenge.

 

In difficult seeing with the Mak, the Svbony at 5mm split 36 Andromedae (+5.5, +6.5, 1.2”) in stiller moments, as did the 5mm BST, although the latter view had the inferior contrast. At 4mm the Svbony still showed little scatter, while the 4mm Nirvana had noticeably more scatter, though also splitting the pair occasionally.

 

In challenging seeing (IV), three components of σ Orionis (+3.8 AB, +8.8 C, +6.6 D, +6.3 E, seps. 29.9” down to 11.6”) were visible in the Svbony at 8mm. Increasing to 4mm (x375) was sufficient to show the fourth component (C) in occasional quiet moments and, while hardly comfortable, showed a little less scatter than the Nirvana. In slightly better seeing (III), the Svbony at 7mm showed the C component a little more clearly than the Morpheus 6.5mm on one occasion, but the honours were reversed on a different evening. At 5mm, the view in the Svbony was very similar to the BCO 10mm with the x2 Altair telecentric multiplier.

 

η Orionis (+3.4, +4.9, 1.8”) showed its companion to the Svbony at 5mm, sitting in the diff. ring. The BCO 10mm + Altair x2 combination was similar, possibly a shade superior on scatter.

 

32 Eridani (+4.7, +5.9, 6.9”) in poor (IV) seeing showed less scatter and better contrast in the Svbony at 5mm, compared with the BCO 10mm + Altair x2, and also showed more of a colour distinction, though this was better still in the Morpheus 9mm.

 

λ Orionis (+3.4, +5.5, 4.5”) was seen as well in the Svbony at 7mm as in the ES 6.7mm, and the diff. rings appeared crisper at 5mm (x300).

 

HR 1902 (+5.7, +6.6, 1.2”) was just split in difficult conditions with the Svbony at 4mm (x375), an easier job than with the Nirvana 4mm, which gave more scatter.

 

6 Trianguli (+5.2, +6.7, 3.7”) was pleasant in the Svbony at 5mm (x300) in good (II) seeing. The BST 5mm gave noticeably more scatter. At 4mm the discs were not as tight and scatter increased, but still a touch better than the Nirvana.

 

γ Arietis (+3.9, +4.6, 7.4”) in good (II) seeing was beautiful in the Svbony at 6mm (x250), with little scatter and two sharp diff. rings on each star. The BCO 6mm was equally sharp, but increased scatter affected the contrast with the background sky.

 

ε Arietis (+4.6, +5.6, 1.3”) in moderate (III) seeing, was just about split in the BCO 6mm, with very little scatter. The Svbony at 6mm (x250) showed almost no scatter, and delivered a view with more contrast, brighter and crisper. The split was wider at 5mm, with similar image quality. Increasing to 4mm and 3mm resulted in more scatter and larger discs, but still not unpleasant. The same target on a poorer evening (IV) was just split in the Svbony at 6mm, but still showed very little scatter and good sky contrast. In the Morpheus 6.5mm the view was very similar.

 

Tegmine (+5.6 AB, +6.3 C, 5.9”, and +5.3 A, +6.2 B, 1.2”) in good (II) seeing, with the Svbony at 8mm, showed a very slight yellow/blue distinction, with little scatter. At 6mm AB was resolved with no degradation of quality. The Morpheus 6.5mm was very similar, possibly having slightly tighter stars. At 4mm (x375), the Svbony effected a split of AB, with some increase in scatter. The view was considerably better than that shown by the Nirvana, where any AB split was masked by stronger scatter.  

 

Achird (+3.4, +7.5, 13.6”) in good (II) seeing with the Svbony at 5mm (x120 in the refractor) showed the faint secondary clearly, and a sharp primary with a couple of diff. rings, though there was some ghosting. The Morpheus 6.5mm was a fraction crisper, but the ghosting was stronger.

 

In addition to the regular observations, when I observed Almach in the Mak, I moved it to just beyond the edge of the field stop. When exiting the field, the star was extinguished rapidly, and only a little light was seen to leak into the view with it placed just outside the stop, commensurate with the levels of scatter I’d seen in other observations.

 

 

Contrast

 

This has already been mentioned in several of the preceding observations. When targeting doubles, reduced scatter and/or ghosting can enhance the contrast with the background sky, an aesthetic improvement, but also useful where fainter companions are to be detected. For Mars/Jupiter/Saturn, contrast can make the difference between seeing a feature or not.

In addition to the comments so far, there was one observation of a planetary nebula:

 

NGC 2392 (Clown Face/Eskimo nebula) in the Svbony at 8mm was very obvious and extended, though no specific structure detected, with good contrast and with the central star seen with direct vision. At 6mm, brightness was reduced and averted vision needed, though this was also true of the Morpheus 6.5mm. The addition of an Astronomik UHC filter did not obviously enhance the view.

 

 

Field Curvature

 

This is a tricky one to assess. Firstly, observers can accommodate differential focus to different extents, and younger eyes can generally manage better – they may not even detect that the field is not flat. Also, FC is affected by the rest of the equipment, and the net effect is often an interplay between eyepiece and OTA. Perversely, an eyepiece with strong FC may seem excellent if used in an OTA imparting an opposite curvature.

 

In mitigation of the first point, my eyes are not the most youthful, and I don’t think much will be hidden on that account. On the second point, I have used three OTAs of different designs and focal lengths, and the Mak, at least, ought to be showing the picture reasonably accurately.

 

As I will be using the zoom with a driven mount, and mostly on compact targets, FC isn’t my top concern, but I did a little investigation.

 

In the Mak 127, Almach was allowed to drift to the edge and no defocusing was observed.

 

In the F/5 Newtonian, 36 Andromedae was focused in the centre of the field with the Svbony at 4mm, and gradually moved to the edge. Some refocusing was required from about 75% from the centre, but still gave a decent image. Beyond around 85%, the stars developed aberrations that could not be refocused. Given the results in the Mak, I ascribe the reflector observations to FC and coma in the OTA, rather than the eyepiece.

 

 

Barlowing

 

The zoom is unlikely to be used with a Barlow, but one test was conducted with a 2x Altair telecentric multiplier at 8mm, comparing the view with the zoom at a native 4mm. There was no discernible difference.

 

 

Blacking out

 

I have previously been pulled up on the distinction between this effect and “kidney beaning”, the latter being apparently very rare in the modern eyepiece. Blacking out, then, is restricted to the phenomenon where there is a comparatively small range of distances between the eye and eye lens that show the image properly, so that correct positioning of the eye becomes critical. This can be helped by a suitable eyecup, comfortable seating, etc.

 

In none of the observations so far have I noticed this effect with the Svbony, though I did see it a couple of times with the BST 5mm and Morpheus 6.5mm.

 

 

Eye relief

 

This was the most obvious drawback of the Svbony. At 6mm – 8mm it was adequate, but hardly comfortable. At shorter lengths, folding back the eyepiece was essential to access the full field, and then care was needed not to touch the eye lens (one session did result in a deposit from eyelashes).

 

I don’t need to wear eye glasses to observe, but I got the impression that it would be difficult or impossible.

 

 

Parfocality

 

As others have reported, the Svbony is not parfocal. Whether or not “nearly parfocal” is a meaningful attribute is moot (and very much so on CN). I found that the slightest touch of refocusing was needed on the longer focal lengths, and a little more at the short end. Other eyes may find that less is required.

 

 

Conclusions

 

In modest scopes, for most of the time, the Svbony held its own against fixed eyepieces ranging from the decent budget end to upper-mid-price.

 

For its most likely use cases, it controlled stray light acceptably well and delivered sharp, engaging views with decent contrast. Over the review period, on average, it outperformed the Nirvana 4mm, BCO 6mm, and BST Starguiders. It probably won and lost to the ES 6.7mm in equal measure, and was outperformed clearly only by the Morpheus.

 

It does not, of course, have a field as wide as some of the comparison fixed eyepieces, so the experience is inevitably diminished to that extent. The main disadvantage is its tight eye relief, particularly at the shorter end, which makes it less comfortable to use than some of the fixed eyepieces.

 

The Svbony zoom is a capable eyepiece and, at the price, should make a mark. With its 3mm-8mm range and small form factor, it could usefully be paired in a travel case with a longer zoom such as the Hyperflex 7.2mm-21.5mm.
I’m happy to have taken a chance on it.

 

 

 

Thanks Zermelo, a very detailed review.

[Louis D]

Nicely done.  You've inspired me to hunt down some doubles sometime in the near future.

I'll have to look for scattering again when I get the chance.  I'd swear I was seeing a bit more in the Svbony than the S-W zoom on Capella, but it could also have been down to undetected dewing of one versus the other.

[Mark at Beaufort]

A really excellent review.

[F15Rules]

Excellent. Clearly a lot of work went into this review and it was an interesting and informative read on all counts. Thank you.

Dave

[Roy Challen]

Excellent, thorough review Zermelo. Particularly interesting (to me at least) are the comparisons to the Baader BCOs and the Hyperflex zoom - my favourite budget eyepieces. 

[Zermelo]

7 hours ago, Roy Challen said:

Particularly interesting (to me at least) are the comparisons to the Baader BCOs and the Hyperflex zoom - my favourite budget eyepieces

Yes, my Hyperflex hasn't had much use recently, but doing the comparisons reminded me how sharp it is. As you know, the downside is that the AFOV falls off quite a bit at the long end. But still good value at £85.

The BCOs are even better value, I've not used a sharper eyepiece than the 10mm.

[Stu]

Just to repeat, really excellent review Paul. Lots of useful info and real life comparisons in there which are very helpful.

When you showed it to me, the Svbony did appear to be a nicely constructed eyepiece and it appears to perform very well. The variable eye relief is probably the biggest negative. The Nag zooms are excellent in that respect being constant at 10mm.

[JeremyS]

What a superbly conducted and reported review. Exemplary, in fact!

[Telescope40]

Great info. Think this report may have tipped the balance and this EP is now on my radar for my EP collection. 
Thx. John 

[Rob]

Very good review. Thanks for posting

Rob

[fullmoon]

Very grateful for this in depth review, thank you.

[cajen2]

Excellent review, Z. All other reviewers (including me!), please take note - this is how it's done!

The only things stopping me from ordering one immediately are that I also have the Hyperflex zoom and will be getting a Baader Hyperion Mk IV shortly, but my biggest problem is eye relief - I can't tolerate very low ER EPs even without my glasses. I also don't really need anything below about 8mm f/l right now.

It's great to see that a high-mag zoom will compete with some decent fixed-length EPs at a relatively cheap price point!

 

[Zermelo]

5 hours ago, cajen2 said:

Excellent review, Z. All other reviewers (including me!), please take note - this is how it's done!

The only things stopping me from ordering one immediately are that I also have the Hyperflex zoom and will be getting a Baader Hyperion Mk IV shortly, but my biggest problem is eye relief - I can't tolerate very low ER EPs even without my glasses. I also don't really need anything below about 8mm f/l right now.

It's great to see that a high-mag zoom will compete with some decent fixed-length EPs at a relatively cheap price point!

 

 

Thanks - it's the first time I've attempted a "proper" review, but I think they can all be useful, if the reviewer is clear about their observing experience (and perhaps their physical condition! )

Yes, I think the eye relief will be a problem if you need eye glasses. Of course, with the short focal lengths of this zoom, it's likely that the exit pupil will be fairly small, so milder astigmatism may not need correction.