henry link
Well-known member
I recently acquired a new Baader Hyperion zoom eyepiece (24mm-8mm). This eyepiece comes with a 1.25" barrel and can also be attached directly to the Zeiss Diascope and Celestron/Synta spotting scopes. What is most interesting about the Baader is that it has, for a zoom, an unusually wide field at the low end of its magnification range, comparable to the Zeiss Diascope zoom. In the US it is available from Alpine Astronomical at a cost of $189. This is less than half the price of the Zeiss zoom eyepiece which could make it interesting to those thinking of purchasing a Diascope. I already own the Zeiss zoom (25.1mm-8.4mm), current Swarovski zoom (23.1mm-7.7mm) and Nikon 20x-60x MC zoom, NOT the MC II (21mm-7mm). All of these are adapted for use on astronomical telescopes. I tested all the eyepieces on an Astro-Physics 92mm f/6.6 APO refractor.
First let me dispense with the question of sharpness at the center of the field. On my AP refractor all of the eyepieces here are perfectly sharp in the center throughout their zoom ranges, just as sharp as fixed magnification eyepieces of very high quality. The birding scopes these eyepieces are used on will virtually always be the limiting factor for center sharpness.
There are performance differences, but they are in the areas of light transmission, contrast, color accuracy, eye relief, field width and off-axis field curvature, astigmatism, distortion and lateral color.
I measured the eye relief and apparent field of each eyepiece at four magnifications on the eyepiece barrel; 20x, 30x, 40x and 60x. I measured the Baader at 24mm, 8mm and two settings in between that would correspond to about 30x and 40x if it were mounted on the Zeiss Diascope. The Baader has “clickstops” which are supposed to correspond to 20mm, 16mm and 12mm. These are ridiculously inaccurate. The 20mm setting actually corresponds to about 13mm, the 16mm corresponds to 10-11mm and the 12mm corresponds to about 9mm. The end stops do seem to be close to 24mm and 8mm.
First the figures for eye relief. These are measured from the eyecup rim set at its lowest position. Distance to the glass of the eyelens would be longer by 4-5mm and with most of these eyepieces (except the Nikon) the eyecups are so wide that the center of a curved eyeglass lens will probably get closer to the eyelens than the rim of the eyecup, adding a couple of mm’s to the effective eye relief. These figures may look short, but I find I can see the entire field at every magnification with all the eyepieces while wearing reading glasses. Only the Nikon’s eye relief “feels” a bit short to me without glasses. All of the eyepieces show the usual dip in the middle of the zoom range.
Swaro 20x-16mm, 30x-12mm, 40x-10mm, 60x-14mm
Nikon 20x-12mm, 30x-8mm, 40x-8mm, 60x-12mm
Zeiss 20x-12mm, 30x-10mm, 40x-8mm, 60x-12mm
Baader 20x-11mm, 30x-9mm, 40x-9mm, 60x-12mm
Now the apparent field widths in degrees:
Swaro 20x-40, 30x-52, 40x-58, 60x-68
Nikon 20x-40, 30x-45, 40x-52, 60x-59
Zeiss 20x-50, 30x-57, 40x-62, 60x-71
Baader 24mm-49, 30x(16.8mm)-56, 40x(12.6mm)-60, 8mm-72
The Baader does have approximately the same apparent field as the Zeiss over its range. Both have wider fields than the the Swaro at low magnifications, but the gap narrows as magnification increases. The Nikon is just not very competitive when it comes to field width.
The clear loser in this group when it comes to light transmission, contrast and color accuracy is the Zeiss, which, compared to the others, is obviously dimmer and lower contrast with a yellow color cast. The Nikon, Baader and Swaro all have very high light transmission and contrast. About as good as it gets for complex eyepieces. The Baader is quite outstanding, possibly the brightest by a hair. It’s easily as bright or brighter than my Pentax 14mm XW and 13mm Nagler, and it gives up almost nothing in brightness and contrast compared to my 16mm Zeiss A-16 Ortho. Color transmission is also very accurate. The Baader and Nikon are nearly indistinguishable with very slight red casts and the Swaro is a tiny bit yellow, not blue like many people report for the complete Swaro scope optics.
There are some interesting differences in off-axis behaviour. Some of this, like distortion, will be exactly the same in other scopes, but field curvature and lateral color in other scopes may be different from my experience.
None of the eyepieces show significant off-axis astigmatism on the AP scope. Edge softness is almost entirely field curvature. At the lowest magnification the Baader has slightly less field curvature than the Zeiss. As magnification is increased field curvature decreases for both until they are about equal with very little curvature at 40x (12-13mm) and beyond. For comparison purposes this is an easy thing to measure by focusing an object at the edge, then moving it to the center and refocus, noting how much the focuser has to be rotated for different eyepieces. I’ve followed the recent discussion about how the Zeiss edge performance compares the the Swaro at low magnification so I also checked the field curvature of the Zeiss and Baader set at their lowest magnification at about 20 degrees off-axis and compared that to the Swaro set at 20x. The Swaro has a very flat field with very little astigmatism or field curvature all the way to the edge of its 40 degree field. Neither the Zeiss nor the Baader is quite as good at the edge of a 40 degree field circle. Their comparable “sweet spot” is about 30 degrees wide. The Nikon is close to the Swaro at low magnification but with a little more astigmatism. At short focal lengths the Baader and Swaro become excellent wide field, long eye relief eyepieces. The Zeiss is nearly as good except for the lower light transmission and contrast.
Distortion varies. There is mild barrel distortion at all focal lengths in the Swaro. The Nikon has very mild pincushion distortion at all focal lengths. There is moderate pincushion in the wider fields of the Zeiss and Baader which increases with magnification as the apparent fields get wider.The Baader has a bit more than the Zeiss, but neither has as much as, for instance, the TeleVue Panoptics at the same apparent field width.
I didn’t see any significant differences in lateral color in my telescope. It’s similar in all the eyepieces at the same distance from the center of the field. There is, of course, more at the field edges at high magnification as the apparent fields widen. I didn’t consider it to be a problem, but it could be worse in faster telescopes.
I haven’t had a chance to try the Baader on the Diascope yet, but it certainly looks like a real alternative. I prefer it to the Zeiss on my AP scope. On the Diascope it would produce a little more magnification than the Zeiss zoom (21x-63x on the 85mm), but would not be waterproof. Optically, I think the Baader is the best zoom eyepiece I’ve tried so far. It manages to combine the wide field width of the Zeiss with the high light transmission, contrast and color accuracy of the Swaro and Nikon, and at a bargain price. I can’t find much to complain about.
Too bad there isn't a Nikon adapter. I think the Baader would probably fit and the Fieldscopes would really benefit from this eyepece.
First let me dispense with the question of sharpness at the center of the field. On my AP refractor all of the eyepieces here are perfectly sharp in the center throughout their zoom ranges, just as sharp as fixed magnification eyepieces of very high quality. The birding scopes these eyepieces are used on will virtually always be the limiting factor for center sharpness.
There are performance differences, but they are in the areas of light transmission, contrast, color accuracy, eye relief, field width and off-axis field curvature, astigmatism, distortion and lateral color.
I measured the eye relief and apparent field of each eyepiece at four magnifications on the eyepiece barrel; 20x, 30x, 40x and 60x. I measured the Baader at 24mm, 8mm and two settings in between that would correspond to about 30x and 40x if it were mounted on the Zeiss Diascope. The Baader has “clickstops” which are supposed to correspond to 20mm, 16mm and 12mm. These are ridiculously inaccurate. The 20mm setting actually corresponds to about 13mm, the 16mm corresponds to 10-11mm and the 12mm corresponds to about 9mm. The end stops do seem to be close to 24mm and 8mm.
First the figures for eye relief. These are measured from the eyecup rim set at its lowest position. Distance to the glass of the eyelens would be longer by 4-5mm and with most of these eyepieces (except the Nikon) the eyecups are so wide that the center of a curved eyeglass lens will probably get closer to the eyelens than the rim of the eyecup, adding a couple of mm’s to the effective eye relief. These figures may look short, but I find I can see the entire field at every magnification with all the eyepieces while wearing reading glasses. Only the Nikon’s eye relief “feels” a bit short to me without glasses. All of the eyepieces show the usual dip in the middle of the zoom range.
Swaro 20x-16mm, 30x-12mm, 40x-10mm, 60x-14mm
Nikon 20x-12mm, 30x-8mm, 40x-8mm, 60x-12mm
Zeiss 20x-12mm, 30x-10mm, 40x-8mm, 60x-12mm
Baader 20x-11mm, 30x-9mm, 40x-9mm, 60x-12mm
Now the apparent field widths in degrees:
Swaro 20x-40, 30x-52, 40x-58, 60x-68
Nikon 20x-40, 30x-45, 40x-52, 60x-59
Zeiss 20x-50, 30x-57, 40x-62, 60x-71
Baader 24mm-49, 30x(16.8mm)-56, 40x(12.6mm)-60, 8mm-72
The Baader does have approximately the same apparent field as the Zeiss over its range. Both have wider fields than the the Swaro at low magnifications, but the gap narrows as magnification increases. The Nikon is just not very competitive when it comes to field width.
The clear loser in this group when it comes to light transmission, contrast and color accuracy is the Zeiss, which, compared to the others, is obviously dimmer and lower contrast with a yellow color cast. The Nikon, Baader and Swaro all have very high light transmission and contrast. About as good as it gets for complex eyepieces. The Baader is quite outstanding, possibly the brightest by a hair. It’s easily as bright or brighter than my Pentax 14mm XW and 13mm Nagler, and it gives up almost nothing in brightness and contrast compared to my 16mm Zeiss A-16 Ortho. Color transmission is also very accurate. The Baader and Nikon are nearly indistinguishable with very slight red casts and the Swaro is a tiny bit yellow, not blue like many people report for the complete Swaro scope optics.
There are some interesting differences in off-axis behaviour. Some of this, like distortion, will be exactly the same in other scopes, but field curvature and lateral color in other scopes may be different from my experience.
None of the eyepieces show significant off-axis astigmatism on the AP scope. Edge softness is almost entirely field curvature. At the lowest magnification the Baader has slightly less field curvature than the Zeiss. As magnification is increased field curvature decreases for both until they are about equal with very little curvature at 40x (12-13mm) and beyond. For comparison purposes this is an easy thing to measure by focusing an object at the edge, then moving it to the center and refocus, noting how much the focuser has to be rotated for different eyepieces. I’ve followed the recent discussion about how the Zeiss edge performance compares the the Swaro at low magnification so I also checked the field curvature of the Zeiss and Baader set at their lowest magnification at about 20 degrees off-axis and compared that to the Swaro set at 20x. The Swaro has a very flat field with very little astigmatism or field curvature all the way to the edge of its 40 degree field. Neither the Zeiss nor the Baader is quite as good at the edge of a 40 degree field circle. Their comparable “sweet spot” is about 30 degrees wide. The Nikon is close to the Swaro at low magnification but with a little more astigmatism. At short focal lengths the Baader and Swaro become excellent wide field, long eye relief eyepieces. The Zeiss is nearly as good except for the lower light transmission and contrast.
Distortion varies. There is mild barrel distortion at all focal lengths in the Swaro. The Nikon has very mild pincushion distortion at all focal lengths. There is moderate pincushion in the wider fields of the Zeiss and Baader which increases with magnification as the apparent fields get wider.The Baader has a bit more than the Zeiss, but neither has as much as, for instance, the TeleVue Panoptics at the same apparent field width.
I didn’t see any significant differences in lateral color in my telescope. It’s similar in all the eyepieces at the same distance from the center of the field. There is, of course, more at the field edges at high magnification as the apparent fields widen. I didn’t consider it to be a problem, but it could be worse in faster telescopes.
I haven’t had a chance to try the Baader on the Diascope yet, but it certainly looks like a real alternative. I prefer it to the Zeiss on my AP scope. On the Diascope it would produce a little more magnification than the Zeiss zoom (21x-63x on the 85mm), but would not be waterproof. Optically, I think the Baader is the best zoom eyepiece I’ve tried so far. It manages to combine the wide field width of the Zeiss with the high light transmission, contrast and color accuracy of the Swaro and Nikon, and at a bargain price. I can’t find much to complain about.
Too bad there isn't a Nikon adapter. I think the Baader would probably fit and the Fieldscopes would really benefit from this eyepece.
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