2020: A Zoom Odyssey
Posted: Mon Feb 03, 2020 4:37 pm
After some thought and deliberation, and over a period of time, I finally acquired a collection of zoom eyepieces. These were the first zooms I had ever owned and I wasn’t totally sure what to expect. I’d read good reviews about the Baader and the Celestron and although there are a few others on the market these two generally seemed to be among the most popular choices. I am pretty convinced that the Celestron is identical to the Meade 8-24mm zoom and both are probably produced by the same OEM. Both the Celestron and Baader zoom eyepieces ostensibly magnify in marked stages. On all of the zooms any magnification between the shortest and longest focal lengths can be achieved, but only the Baader has definite (but subtle) click-stops.
However, they are all significantly different in particular ways. Primarily in their respective retail prices. With the Hyperion basically being twice as expensive as the Celestron unit, which in turn was twice the retail price of the Sky-Watcher. The Baader is larger and heavier than both the Celestron and Sky-Watcher zooms. The BHZ is the only one that can utilise a 2” skirt even though it is technically only a 1.25” eyepiece. The Baader zoom apparent field of view varies between 50° and 68° while the Celestron varies between 60° and 40° (according to Baader and Celestron respectively). I have no data for theAFOV of the Sky-Watcher zoom. Apart from an undercut it appears to be almost identical to the now discontinued ‘Orion Explorer II 7-21mm Zoom’. Orion claim an apparent field of view of 30° at 21mm and 43° at 7mm. There is a TS Optics equivalent to the Sky-Watcher zoom. TS Optics claim 50° at 21mm and 40° at 7mm. There are alternative claims of a purported 54° (at 7mm) to 38° (at 21mm) for the same eyepiece.
Baader Mk IV Hyperion Universal - Zoom
The first zoom I received was the Hyperion. Not uncommon with Baader products it comes supplied with various extras and I also purchased the 2.25x Hyperion Zoom Barlow at the same time. The first thing that I noticed was that the eye lens dust cap on the zoom eyepiece wasn’t easy to remove. This can be an important issue for me as I am physically disabled. This was later rectified when I had to return the zoom to the retailer when a huge piece of internal debris dropped into the field of view effectively rendering the eyepiece useless. The retailer rapidly replaced the faulty zoom, and the new one not only seemed to work perfectly, but had a much better fitting eye lens cap.
I got a chance to test the BHZ first during a rich field session with my modified ST102. I decided to take only two eyepieces out with me, the other being a 31mm Baader Hyperion Aspheric. This certainly simplified things for me as I could now easily get both eyepieces, theOTA , finder, and diagonal all in the same carrying bag. The zoom replaced the usual rich field kit of a 19mm TeleVue Panoptic, a 14mm Baader Morpheus aka ‘The Dalek’ and a 9mm Celestron X-Cel LX (or alternatively sometimes an 8mm TS Optics Planetary HR ). Inevitably most of the session was with the BHZ ‘Super Dalek’. The transparency wasn’t too good although the overall seeing seemed like a decent Antoniadi ‘I’. The first thing I noticed was the smaller FOV compared to the 76° Morpheus, although I did actually expect to see a difference. I am not too sure of Baader’s claims of eye relief distance as I discovered that this varied with magnification. I seemed to be pushing my eye right into the eye lens quite often to see all of the FOV . The Pleiades and other open clusters looked very sharp even at higher magnifications. There was very little edge distortion and the overall image was very clear with a pleasing flat field. Zooming in on Caldwell 14 (Perseus Double Cluster) and double stars was great fun. Cor Caroli looked quite resplendent at 62.5x and was easily as good as with the 8mm Planetary HR . The BHZ has since become my most used zoom.
Sky-Watcher 7-21mm Zoom
The Sky-Watcher ‘baby’ zoom is probably the sort of eyepiece that those who generally denigrate zooms are referring to. It is a small, lightweight and compact unit roughly 8cm tall (not including eyeguard height). As a consequence the field of view is somewhat diminished compared to the other three. Mine actually has no brand name on it. The housing appears adequately constructed with a chromed brass drawtube that includes an undercut. In my experience the undercut was not problematical. The rubber eyeguard is similar to the one on the Celestron 8-24mmEP and can also be rolled down. At first in use I tended to prefer it in the rolled down position for the shorter focal lengths. If you’re not careful the eyeguard can suddenly pop up from that position and smack you in the eye! I find when observing at around 21mm to 15mm the eyeguard is better in the default rolled up position as the eye relief seems quite long.
First light was on a twilight setting Moon in a 90mm Orion Maksutov giving me between 59.5x and 178.5x. Due to the conditions the best magnifications I achieved were about 90x to around 130x. It directly compared well with 14mm and 20mm Bresser 60° ‘Plossls’, although the field of view of the zoom was smaller of course. Occasionally I could detect some false colour right at the edge of the field stop. I next got to use it with a Sky-Watcher 72ED Evostar DS-Pro. My original plan was to start with low power rich field observing and then use the zoom paired with a Barlow on the Moon when it had risen high enough. Due to the fact I’d miscalculated the low lunar altitude I ended up using the baby zoom on its own (sans Barlow) for some unintended deep sky observing. First target was the Perseus Double Cluster, followed by several of the open clusters in Cassiopeia. I then turned towards the Beehive Cluster and some double stars, including Cor Caroli. The baby zoom gave between 20x and 60x on the ED72. I directly compared the zoom set at approximately 12mm with a 12mm Celestron X-Cel LX on the Beehive, Double Cluster and Cor Caroli. The zoom surprisingly held up very well and only showed any astigmatism right at the edge of field. The zoom action is smooth and easy to operate. This is a nice little zoom, although personally I would prefer to use it for lunar and planetary observing. Its smallFOV would generally tend to preclude it being used for open clusters even though it did cope quite adequately in the ED72. Overall the Sky-Watcher zoom is well worth what it cost.
Celestron #93230 8-24mm and Meade 4000 Zooms
I didn’t originally purchase the Celestron to be used with a Barlow in the ST102. I had envisioned it as a back up or alternative to the Hyperion if the Baader zoom hadn’t worked out. However, it performed admirably paired with a 2.5x Celestron Luminos Barlow, giving convincingly wide and pleasant views of the Moon. The Celestron housing is about 10cm tall (eyeguard rolled down) and 4.5cm wide with a chromed brass drawtube with an undercut. I found that I tended to prefer the eyeguard in the default rolled up position at 24mm. There was also a slight amount of kidney beaning if the eye positioning wasn’t just right at the longest focal length. The ‘baby’ Sky-Watcher by comparison stands at 8cm (eyeguard rolled down) and is about 4cm wide. Furthermore, the Celestron zoom feels well made and substantial belying its reasonable price. At shorter focal lengths theFOV appears like a good 60° although the 40° is distinctly noticeable at 24mm. The Celestron #93230 is supplied with a nice and practical ‘vase’ shaped plastic container with a threaded screw-off lid. It also performed well in a 127mm Sky-Watcher Maksutov. The range was 62.5x to 187.5x although the most useful magnifications for lunar viewing were between around 125x to 187x (12mm ~ 8mm). It is now used regularly with my Maksutovs, and with my small refractors combined with a Barlow. The Meade 4000 is identical to the Celestron except for cosmetic differences. The drawtube barrel on the Meade is not chrome although it also features an undercut. The Celestron and Meade zooms have identical focal planes and could potentially be used side by side in a binoviewer. Interestingly the Meade has more sophisticated markings on its housing to denote focal length more accurately. Although this essentially seemed like a good idea I soon discovered that the markings aren’t particularly easy to make out in the dark.
TeleVue 3-6mm Nagler Zoom
I realised that this zoom was perfect for my telescope focal lengths. It is beautifully made and the zoom mechanism works perfectly. There are definite click stops between the focal lengths although any length can effectively be selected between 6mm and 3mm. As you would expect this is a small 1.25” eyepiece and has a correspondingly close eye relief of about 10mm. TheFOV on all focal lengths is a constant 50º. It’s not often that I’m totally astounded by an eyepiece, but I am by this. It is par-focal so zooming in for high planetary observing is nicely straightforward. I had a recent view of a twilight Jupiter with this zoom and my 102mm Altair Starwave. The clarity and sharpness were outstanding. Even at 238x it wasn’t a bad image, although that was definitely pushing it in the conditions. However, I just couldn’t resist it. The ability to start at 119x and gradually increase the magnification until I achieved a balance between magnification and clarity with it was most satisfying. Later I split double stars, including the Double Double.
Pentax XL 8-24mm Zoom
I believe this was originally intended for a Pentax spotting scope. Which I find a bit weird as it weighs in at over half a kilo (550g). It is also 1.25” and ranges from 24mm to 8mm. Ostensibly it is very similar to the Baader, although it has a substantially heavier and stronger build, and is apparently waterproof. It has no 2” skirt option. The Pentax almost feels like you could drop kick it without causing it any damage (I didn’t try this). Unlike the Hyperion it doesn’t come with included extras although it is supplied with a large bolt case. It also features a twist-up eyeguard and the zoom mechanism works smoothly with no click-stops. The mechanism, which utilises a waterproof seal, feels a little stiff at first but improves with use. This is a fairly weighty eyepiece so I placed the drawtube barrel into a 1.25” (two screw) Baader adapter in a 2” diagonal. Most of my scopes and all of my refractors have aftermarket Baader adapters. In this way the twist mechanism wouldn’t work the eyepiece loose. Pentax claim that theFOV starts at 38° at the longest focal length then opens up to 60°, which seems about right. The optics (six elements in four groups) in this eyepiece are excellent and include lanthanum glass. The brightness, contrast and clarity are astounding for a zoom. I had the best image I’ve ever seen of the Ring Nebula with the XL. This zoom has a distinct edge on the Baader in many respects. I’m fairly convinced that this is the best zoom eyepiece of its class.
Pentax XF 6.5mm to 19.5mm Zoom
The smaller XF sibling has a 6.5mm to 19.5mm focal length and anAFOV of 60° (at 6.5mm) to 42° (at 19.5mm). The eye relief varies between 11mm to 15mm. Like the XL there are six multicoated lenses in four groups. It weighs in at 240g standing 90mm tall with a maximum diameter of 50mm. The XF is considered by many to be inferior to the XL. I’ve used it predominantly in my f/ 7.5, Sky-Watcher Evostar ED80. The main bones of contention with the XF seem to be with perceived lateral astigmatism and a lower light transmission. I have seen some small amount of edge distortion although on-axis it is excellent. The overall transmission may not be as high as the XL in comparison but the lanthanum glass imparts a wonderful tone and the colour separation is beautiful to behold. The main benefit for me with this little zoom was that it was lightweight, straightforward and effortless to manipulate. I’ll certainly be taking it out again.
However, they are all significantly different in particular ways. Primarily in their respective retail prices. With the Hyperion basically being twice as expensive as the Celestron unit, which in turn was twice the retail price of the Sky-Watcher. The Baader is larger and heavier than both the Celestron and Sky-Watcher zooms. The BHZ is the only one that can utilise a 2” skirt even though it is technically only a 1.25” eyepiece. The Baader zoom apparent field of view varies between 50° and 68° while the Celestron varies between 60° and 40° (according to Baader and Celestron respectively). I have no data for the
Baader Mk IV Hyperion Universal - Zoom
The first zoom I received was the Hyperion. Not uncommon with Baader products it comes supplied with various extras and I also purchased the 2.25x Hyperion Zoom Barlow at the same time. The first thing that I noticed was that the eye lens dust cap on the zoom eyepiece wasn’t easy to remove. This can be an important issue for me as I am physically disabled. This was later rectified when I had to return the zoom to the retailer when a huge piece of internal debris dropped into the field of view effectively rendering the eyepiece useless. The retailer rapidly replaced the faulty zoom, and the new one not only seemed to work perfectly, but had a much better fitting eye lens cap.
I got a chance to test the BHZ first during a rich field session with my modified ST102. I decided to take only two eyepieces out with me, the other being a 31mm Baader Hyperion Aspheric. This certainly simplified things for me as I could now easily get both eyepieces, the
Sky-Watcher 7-21mm Zoom
The Sky-Watcher ‘baby’ zoom is probably the sort of eyepiece that those who generally denigrate zooms are referring to. It is a small, lightweight and compact unit roughly 8cm tall (not including eyeguard height). As a consequence the field of view is somewhat diminished compared to the other three. Mine actually has no brand name on it. The housing appears adequately constructed with a chromed brass drawtube that includes an undercut. In my experience the undercut was not problematical. The rubber eyeguard is similar to the one on the Celestron 8-24mm
First light was on a twilight setting Moon in a 90mm Orion Maksutov giving me between 59.5x and 178.5x. Due to the conditions the best magnifications I achieved were about 90x to around 130x. It directly compared well with 14mm and 20mm Bresser 60° ‘Plossls’, although the field of view of the zoom was smaller of course. Occasionally I could detect some false colour right at the edge of the field stop. I next got to use it with a Sky-Watcher 72ED Evostar DS-Pro. My original plan was to start with low power rich field observing and then use the zoom paired with a Barlow on the Moon when it had risen high enough. Due to the fact I’d miscalculated the low lunar altitude I ended up using the baby zoom on its own (sans Barlow) for some unintended deep sky observing. First target was the Perseus Double Cluster, followed by several of the open clusters in Cassiopeia. I then turned towards the Beehive Cluster and some double stars, including Cor Caroli. The baby zoom gave between 20x and 60x on the ED72. I directly compared the zoom set at approximately 12mm with a 12mm Celestron X-Cel LX on the Beehive, Double Cluster and Cor Caroli. The zoom surprisingly held up very well and only showed any astigmatism right at the edge of field. The zoom action is smooth and easy to operate. This is a nice little zoom, although personally I would prefer to use it for lunar and planetary observing. Its small
Celestron #93230 8-24mm and Meade 4000 Zooms
I didn’t originally purchase the Celestron to be used with a Barlow in the ST102. I had envisioned it as a back up or alternative to the Hyperion if the Baader zoom hadn’t worked out. However, it performed admirably paired with a 2.5x Celestron Luminos Barlow, giving convincingly wide and pleasant views of the Moon. The Celestron housing is about 10cm tall (eyeguard rolled down) and 4.5cm wide with a chromed brass drawtube with an undercut. I found that I tended to prefer the eyeguard in the default rolled up position at 24mm. There was also a slight amount of kidney beaning if the eye positioning wasn’t just right at the longest focal length. The ‘baby’ Sky-Watcher by comparison stands at 8cm (eyeguard rolled down) and is about 4cm wide. Furthermore, the Celestron zoom feels well made and substantial belying its reasonable price. At shorter focal lengths the
TeleVue 3-6mm Nagler Zoom
I realised that this zoom was perfect for my telescope focal lengths. It is beautifully made and the zoom mechanism works perfectly. There are definite click stops between the focal lengths although any length can effectively be selected between 6mm and 3mm. As you would expect this is a small 1.25” eyepiece and has a correspondingly close eye relief of about 10mm. The
Pentax XL 8-24mm Zoom
I believe this was originally intended for a Pentax spotting scope. Which I find a bit weird as it weighs in at over half a kilo (550g). It is also 1.25” and ranges from 24mm to 8mm. Ostensibly it is very similar to the Baader, although it has a substantially heavier and stronger build, and is apparently waterproof. It has no 2” skirt option. The Pentax almost feels like you could drop kick it without causing it any damage (I didn’t try this). Unlike the Hyperion it doesn’t come with included extras although it is supplied with a large bolt case. It also features a twist-up eyeguard and the zoom mechanism works smoothly with no click-stops. The mechanism, which utilises a waterproof seal, feels a little stiff at first but improves with use. This is a fairly weighty eyepiece so I placed the drawtube barrel into a 1.25” (two screw) Baader adapter in a 2” diagonal. Most of my scopes and all of my refractors have aftermarket Baader adapters. In this way the twist mechanism wouldn’t work the eyepiece loose. Pentax claim that the
Pentax XF 6.5mm to 19.5mm Zoom
The smaller XF sibling has a 6.5mm to 19.5mm focal length and an