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Starbase 'Orthoscopic Plossls'

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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. 



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” 




~ 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.




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. 




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. 




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.




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. 




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. 



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.




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




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

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  • 2 weeks later...




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.




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.



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.




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.




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. 




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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