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Starbase 'Orthoscopic Plossls'


Nightspore
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The Starbase four element ‘orthoscopic’ series of eyepieces are distributed by Takahashi Seisakusho Ltd. There are supposedly five in the range consisting of: 20mm, 18mm, 14mm, 9mm and 6mm focal lengths. However the 18mm doesn’t seem to be available outside of Japan. The 6mm and 14mm versions are bundled with the Starbase 80 telescope package. 

 

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The Starbase achromat and the eyepiece series are apparently both made by the Kubota Optical Corporation in Hanamaki, Japan. The eyepieces are not a traditional Abbe orthoscopic design and are purportedly an asymmetrical doublet defined and designated as an Orthoscopic Plossl (Orthoscopic/PL). They are recommended for use with focal ratios up to f/6. 


“In the early days, it was made by Cook in England and Steinheil in Germany. This is an achromat type eyepiece that combines two Ramsden lenses. A well-made Japanese-made eyepiece is an almighty eyepiece that can be used from low to high magnification because ghosts are not noticeable and spherical aberration and distortion are small. By the way, NIKON's orthoscopic eyepieces, which are still very popular today, were PL type” 

 

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~ op cit (diagram and definition from the Scopetech webpage).

 

Etymologically the compound adjective ‘orthoscopic’ literally means corrected vision. Unlike most contemporary modern eyepieces the Starbase series probably aren’t edge-blacked. They feature a ‘retro’ volcano top without rubber eyeguards. The eyepieces each have a single high quality coating as opposed to being multi-coated. The proclaimed rationale behind using only a single coating of superior quality is that it gives much better transmission than relatively inexpensive mass produced multi-coatings. Except for the barrel undercut they have the vintage appearance of an erstwhile era. The AFOV varies between 43° and 53° throughout the range.

 

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The 20mm has a 45° AFOV and 14mm of eye relief. I make the eye lens a decent 17mm with a 15mm field stop. I find this a quite pleasant eyepiece to use. Around 13-14mm is my preferred eye relief distance. The field stop is sharp and defined, as the stops are throughout the range. The chromed brass barrel is high quality with good baffling and has a filter thread. Although, to my chagrin, I discovered my broadband Explore Scientific OIII and Astronomik UCE-E filters would only thread in a small amount. This problem was the same with the other focal lengths. 

 

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It should be enough when placed in a 1.25” diagonal. I would have concerns about it coming loose in a 2” diagonal or a Newtonian focuser. My Baader filters had no problems in any of the four eyepieces. Interestingly the ES OIII has no issues at all threading smoothly and completely into my 1.25” Tele Vue Everbrite and Baader BBHS diagonal nosepieces. So, no surprise there then with the known compatibility issues of Japanese filter threads! The end caps fit well and the undercut gave me no problems. In my f/5.8 Sky-Watcher Evostar 72ED DS Pro, at 21x for a 3.4mm exit pupil, it gave nearly a hundred and twenty nine arc minutes of true field of view. This is nigh on four and a third Full Moons and only around twelve arc minutes less than my 25mm Ohi-made Abbe orthoscopic. I could just about get the entire Coat Hanger (Brocchi’s Cluster) in the FOV. The 20mm eyepiece showed an abundantly bright, well contrasted image, displaying excellent transmission and on-axis acuity. However there is some lateral astigmatism approaching the field stop. I did expect this with the f/5.8 Evostar as it is a bit unforgiving with some eyepiece designs. I tend to observe mainly on-axis anyway so it didn’t really bother me. Apart from the thread issue the ES OIII worked well with the 20mm giving me a vivid view of M27 and nicely revealing the Eastern and Western Veil Nebulae. 

 

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At 53° the 14mm has the widest AFOV,  and in my opinion it definitely shows. My first impression was of a very agreeable field of view for such a physically small eyepiece. I make the eye lens 15mm and the field stop at least 13mm. I find the 12mm eye relief to be quite comfortable. Eye placement is undemanding and the eyepiece has a good ergonomic feel about it. Although it also showed some astigmatism towards the field stop. The transmission was bright, well above average, and I even got a glimpse of M57 at 30x. When deployed in a 2x Vixen Deluxe Barlow for 60x it was equally sharp, the astigmatism had disappeared, and it displayed no vignetting. I found both Hercules clusters at 60x with ease and split several doubles including the beautiful γ Andromedae.

 

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The 9mm has a 45° field and the 7mm eye relief is about average for its focal length. By comparison my 9mm Circle- T Abbe has a 7.6mm eye relief. When used in conjunction with the Vixen Barlow in my 72ED DS Pro the 9mm Orthoscopic/PL really came into its own as a planetary eyepiece. The Barlow slightly improved the close eye relief. Both Saturn and Jupiter were very sharp at 93.3x. Colour separation and contrast were excellent. The Cassini Division and some surface detail on Saturn were easily observed as was Titan. I was impressed with the amount of detail I could actually see as Jupiter approached transit. Although occasionally I thought I detected a tiny bit of scatter. The planet is quite bright and only a few weeks from opposition though. I was also using a Baader Neodymium filter in the diagonal nosepiece which may have contributed to this effect in some way. It was a damp and dew laden early morning session. With excessive humidity filters can often have a tendency to fog slightly in the nosepiece. I believe I also occasionally saw a hint of the reflection of my own cornea, which may be a consequence of the single coating. After some use this disappeared. In later sessions I didn’t notice either phenomena. The barrel undercut plays well in the Vixen Barlow as it has no compression ring. 

 

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With only 4mm of eye relief and a 43° apparent field the 6mm Orthoscopic/PL is the least ergonomic of the quartet. Again, compared to an Abbe of the same focal length, it has almost a millimetre less eye relief. Images of Saturn and Jupiter used without a Barlow in the 72ED at 70x were very sharp and bright. The intensity of the rich colours and excellent contrast impressed me.  I was immediately quite taken with the 6mm O/PL, especially when used in the Vixen Barlow. The volcano top almost certainly contributed to the comparative ease of viewing and eye positioning. I’d expected it to be more demanding to use, so this was a pleasant surprise.  At 140x (with the Barlow) the 6mm O/PL gave an approximate 0.5mm exit pupil. I split ε Boötis and I thought it was one of the best views of the binary I’ve had so far this year. As Cassiopeia got higher in the sky I discovered ι Cassiopeiae also split beautifully. I’m convinced these views were enhanced by the above average transmission of the single coating. 

 

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Saturn still looked excellent even when it was past transit. During the first session it wasn’t quite as sharp on Jupiter at 140x. This wasn’t surprising however as the seeing was only average and the transparency was relatively poor. What was surprising was just how well the 6mm performed on Jupiter at 140x in a 72mm ED doublet. In a later session of better conditions I could see what appeared like Ganymede’s shadow on the surface near the limb. I actually first witnessed this at 93x with the Barlowed 9mm. I knew Ganymede would eventually become visible as it transited the surface. I impatiently switched back to the 6mm as I wanted to view this emergence before I lost the transparency. Eventually I was rewarded with the bright point of light of Ganymede seemingly separating itself from the planetary limb. Overall I like these eyepieces. Although purists may find they perform better at f/8 or slower. If you’re into Japanese retro eyepieces at a reasonable price I’m pretty sure you’ll like them too.

Edited by Nightspore
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Thanks Nightspore, I have been educated. Although I have heard of orthoscopics, I have no experience of them and neither do I have any knowledge of what they are. Therefore, this was an interesting read that has genuinely given me that little extra useful knowledge.

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Just now, Marmot said:

Thanks Nightspore, I have been educated. Although I have heard of orthoscopics, I have no experience of them and neither do I have any knowledge of what they are. Therefore, this was an interesting read that has genuinely given me that little extra useful knowledge.

 

You're welcome.

 

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When most people talk about 'orthoscopics' they're referring to the Abbe design.

 

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Baader BCO's are based on a Zeiss modification to the original Abbe.

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  • 2 weeks later...

 

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The Starbase O/PL’s were originally acquired for my 102mm Sky-Watcher SkyMax Maksutov Cassegrain. Its focal ratio of f/12.7 should ameliorate any aberration problems that were noticed in the faster scope. The initial rationale behind buying these eyepieces was that they were relatively light in weight, ergonomic (I like volcano tops), and had good build quality. The whole SkyMax grab and go kit needed to be light and portable and fit into a small holdall-type bag.

 

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Everything, including the diagonal and the 7-21mm zoom eyepiece, were chosen as much for weight as optical performance and quality. Technically the SkyMax should have a 2.1 light grasp ratio over my 72ED DS Pro. However, the catadioptric has an obstruction (Secondary or Gregory Spot) and the light is reflected as opposed to being refracted. As a consequence reflecting telescopes generally lack the contrast and acuity of refractors. Sir Patrick Moore once claimed that serious lunar observing starts with a 6” reflector or a 4” inch refractor. A 150mm reflector aperture is 1.5x larger than a 100mm refractor aperture. Using this ratio the 102mm Maksutov roughly equals a 68mm refractor. There is an old joke that 4” Mak’s are only good for looking at the Moon. They do have a good reputation for splitting double stars. I’ve owned the 102mm StarMax for a long time and tend to predominantly use it as a lunar grab and go scope.

 

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The 20mm Starbase gave me a nice view of Saturn and Jupiter at 65x. It was when I started using the 14mm it started getting interesting. Although I did notice the undercut snagging occasionally when swapping eyepieces. The three screws of the Baader helical compression ring can often be a little finicky with barrel undercuts. The 14mm O/PL gave a fairly sharp 92.8x. The seeing was above average, but not as good as the previous night. Jupiter’s GRS was just noticeable near the western limb and would be about central at transit (03:20). Ganymede, Callisto, and Io were close together on the western side of the planet with Europa on the opposite side. I could perceive colour in the moons and discern some Jovian surface detail. As the planet rotated the GRS became more easily visible. I decided it was time for the 9mm ‘Orthoscopic Plossl’. At 144x I lost a lot of acuity and furthermore there appeared to be quite noticeable ghosting. Jupiter is very bright at the moment though with a visual magnitude of -2.8.

 

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Inevitably I switched back to the 14mm and even the Orion zoom for a while. I still couldn’t manage much above 100x though. Saturn fared better with the 9mm but even then I didn’t think it was as sharp as it could have been. This was probably more to do with conditions than anything else. When Jupiter reached transit I still wasn’t satisfied with the 9mm although around an hour later I had a much sharper view at 144x with no ghosting. I think that 144x at an 0.7mm exit pupil was pushing the Mak’s optics a bit much. Undoubtedly further than they should have been in the conditions. I’m convinced it would have been much easier to get the same exit pupil with a refractor. By comparison the 72ED will reach 140x (0.5mm exit pupil) comparatively easily.

 

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To finish off I decided to split some early morning twilight doubles. These included Almach, Polaris, Sheliak, Struve 2470/74 and Epsilon Lyrae. In my experience Mak’s tend to make the first diffraction ring a bit brighter than refractors. This is possibly due to the influence of the Gregory Spot. Lastly I split the three components of Iota Cass beautifully at 216.6x with the 6mm O/PL (0.47mm exit pupil). I’d re-calibrated the Rigel finder earlier in the week. The ‘QuikFinder’ is notorious for parallax issues and I really had to concentrate to find Iota in the early dawn. It was worth the effort however. The 6mm and 14mm Starbase seem to be the most used of the four eyepieces. The 6mm is quite exceptional in many respects. 

 

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I’m a bit ambivalent about comparisons between the Evostar and the StarMax. The Maksutov effectively has a limiting magnitude of 12.74 compared to the 11.99 of the smaller ED doublet. I can often reach around 140x with either of them for planetary observing. Although, at the end of the day, I personally prefer the better visual acuity and contrast of the smaller refractor. The 102mm aperture has a Dawes limit of 1.14 arc seconds in comparison to the 1.61 arc seconds of the 72mm. The question is does 0.47 of an arc second and 0.75 of magnitude really make that much of a difference? These are basically backyard telescopes small enough to be carried in a flight bag.




 

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  • 2 weeks later...

I compared four eyepieces of a similar focal length in two telescopes. In white light and then later at night time. The scopes were an f/13.8, 90mm Orion StarMax Maksutov Cassegrain and an f/5.8 Sky-Watcher 72ED DS Pro Evostar doublet. The catadioptric was used for terrestrial daylight targets and the refractor was used for astronomical targets. 

 

The eyepieces were: 

 

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1/ A 20mm Starbase orthoscopic Plossl (Kubota Optical Corporation)

2/ A 20mm GSO Super Plossl (Guan Sheng Optical)

3/ An 18mm Astro Hutech orthoscopic (Ohi Optical)

4/ An 18mm Takahashi orthoscopic (Takahashi Seisakusho)

 

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The terrestrial targets included trees, distant houses, telegraph poles, the occasional bird and a field. The magnifications were 62.5x (20mm) and 69.4x (18mm). Predictably the eyepieces gave similar views although the slightly wider field of the GSO Plossl was noticeable. The best daylight transmission seemed to be the Starbase although the GSO wasn’t far behind. Contrast and acuity were better with the Abbe orthoscopics although the Takahashi showed a distinct contrast advantage over the Hutech and revealed more detail. The Ohi was slightly brighter however, possibly indicating a touch better transmission.  

 

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The 72ED gave magnifications of 21x and 23.3x. Astronomical objects included: Albireo, M29, the Double Cluster, the Owl Cluster, M103, NGC 663, M31, Stock 2, M27, the Western Veil Nebula, Brocchi’s Cluster and NGC 6883. A broadband OIII filter was used for M27 and the Veil Nebula.The Hutech orthoscopic showed no astigmatism that I could detect. The Takahasi Abbe showed a tiny amount right next to the field stop edge itself. The Takahashi has a 44° AFOV however and I’m guessing the extra 2° is gained by giving it a slightly larger field stop, not unlike the Baader BCO’s. Baader intended this extra field to aid target location and the BCO orthoscopics also display some lateral astigmatism after 42°. It’s a possibility Takahashi intended something similar or it was designed as a form of visual ergonomics. In use Takahashi Abbe orthoscopics feel slightly larger than they actually are.

 

The GSO ‘Super Plossl’ was sharp almost to the field stop. GSO Plossls seem remarkably good at f/5.8. It certainly held its own with the others and had remarkably good colour separation considering what it cost. The Starbase showed some distortion approaching the field stop which is interesting considering it only has a 45° field of view. I suspect the entire Starbase range are essentially intended for slower scopes. It was very good on faint nebulae although I still wasn’t convinced the contrast was as good as with the Takahashi. The Starbase did have the best transmission as a whole. Most probably due to its single coating. The Takahashi, unsurprisingly, gave the most contrasted views out of the four. At one stage I’m pretty sure I saw M57 with it at 23.3x. I couldn’t see the ‘ring’ but it appeared as a fuzzy spot. Both orthoscopics displayed greater contrast than the Plossls, although I expected that. 

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  • 7 months later...
Posted (edited)
35 minutes ago, Stephen Waldee said:

 

Congratulations: THIS is a "model review" of eyepiece performance! It satisfies every question one might think of and should set a standard for -- ahem -- other forums: which present "reviews" in which many pairs of eyepieces are matched, a preference of each pair chosen, by watching the Trapezium of M-42 over a period of five hours, while the object slowly sets into the tremulous air; then at the end, the winner of a couple dozen matched pairs is awarded the prize! (I was gobsmacked with horror at that article and decided NEVER to look at another post by the culprit.)

 

Steve & Regina, Ivins UT
http://reginacelestial.byethost3.com
or 
http://celestialregina.x10.mx

 

Thanks. My reviews are more 'man on the Clapham omnibus' than technical anorak. I'm a bit ambivalent about the Kubota Starbase series. I like their overall ergonomics but the undercut does them no favours and the single coating makes their use limited. I originally envisioned them as similar to Abbe orthoscopics and used as dedicated lunar eyepieces. The inherent ghosting and scatter effectively precludes them from this. The high transmission makes them good for deep sky and doubles though.

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9 minutes ago, Stephen Waldee said:

 

IMO, your eyepiece review article above IS a technical analysis (merely not done with measuring instruments other than the sensitive trained EYE, from encyclopedic knowledge.) It's not "subjective".  It's not "aesthetic" as in trying to compare vaguest impressions through a scope at the bottom of the swimming-pool of turbulent atmosphere.  It does not try to go into reams of words about broken Airy disk appearance.  Rather it discusses the construction; the functionality; and the characteristics of these physical objects: intelligently, from a completely informed perspective.  It is not casual, not trivial, not colloquial, and not superficial.  It is repeatably informative: I am absolutely CERTAIN that if I had these in hand, I would very likely rather immediately see many of these things myself--but would probably MISS some that you have documented.  As i said, it is a MODEL of a review of eyepieces.  Because it was not done with a laser and ray-trace using a simulated point source (as Celestron does in their "clean room", which I've visited) does not means it's not technical.  Congratulations AGAIN for what you are able to do here!

 

Steve & Regina, Ivins UT
http://reginacelestial.byethost3.com
or 
http://celestialregina.x10.mx

 

Thanks, I appreciate your appreciation. I once bought a 7mm Kokusai (Ohi) orthoscopic from TS Optics. When I first daylight tested the EP it appeared to have a bright point of light near the centre of field. I'd not seen this before in an eyepiece. I surmised that one of the elements had been damaged or chipped in some way during construction. 

 

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I contacted TS and explained that there was basically a point of bright light near the centre of the field of view. I suggested it was possibly a chip or defect in a lens element which caused the anomalous point of light. Naturally they said they'd replace it and could I return it. They duly replaced it with one that was perfect. A few weeks later I received a PDF of a complete analysis of the eyepiece conducted in the optical laboratory of Markus Ludes. They'd never seen anything like this either. They had spent considerable time firing laser beams through it, making spectrographic analyses, and generally testing for everything and anything. Copious amounts of data were included with the PDF. Their conclusion was that there was possibly a chip or defect in a lens element which caused the anomalous point of light. 

 

Germans never do anything by halves.

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Hi, thank you for a great review. I am wondering, can the barrel on these Starbase Orthos be unscrewed from the eyepiece top and reversed (eyepiece fitted from the filter side of the barrel)?

 

I am not very keen on these safety undercuts and tend to reverse the barrels to get the undercut out of the way.

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5 hours ago, PeterD said:

Hi, thank you for a great review. I am wondering, can the barrel on these Starbase Orthos be unscrewed from the eyepiece top and reversed (eyepiece fitted from the filter side of the barrel)?

 

I am not very keen on these safety undercuts and tend to reverse the barrels to get the undercut out of the way.

 

Thanks. The barrels can definitely be unthreaded and reversed. I tried it tentatively with the 20mm, but didn't thread very far so as not to wear away the matte blacking in the baffling. So I don't know if it will thread completely. One caveat with these eyepieces is that they only have a single coating. There may be ghosting on bright objects.

 

A lot of Japanese threads have compatibility issues. Although the same can be said for most *Tele Vue threads. IME Baader and GSO have the most consistently compatible threads.

 

*TV eyepieces are predominantly made in Taiwan by BASO Precision Optics. TV Plossls and the DeLite range are manufactured in Japan. The OEM is unknown, although I suspect Ohi.

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