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Unusual 4.8mm Orthoscopic


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This unusual ‘alleged’ Abbe fully multi-coated orthoscopic has a focal length of 4.8mm. I say ‘alleged’ as I don’t actually know if this is indeed a genuine Abbe design. From what I can gather it has two lens groups consisting of a triplet and a single lens. So, the odds are it is an Abbe eyepiece and very probably manufactured in China. Mine has no brand name but these eyepieces have also been sold as Kson, Ascension, Apogee and University Optics orthoscopics.




The eyepiece has no dust caps but it is supplied in its own plastic bolt case. The housing is almost exactly 50mm tall and appears to include the tapered barrel as an integral part of its aluminium housing. The barrel itself has a 28.5mm filter thread and is competently baffled. I discovered that my Baader, GSO and Lumicon filters all threaded fairly smoothly into the barrel. However, Meade and Barsta 2x Barlow elements were not easily threaded in all of the way. A GSO 2x short Barlow element threaded perfectly. The eyepiece features a flip-up rubber eye guard which is a rarity on most orthoscopics. I couldn’t separate the barrel by unthreading it and I assume it is essentially a monocoque design, which is also unusual in my experience. The housing is very light as a whole and feels a fair bit lighter in the hand when compared to both a 5mm Kokusai Kohki orthoscopic and a 6mm Vixen NPL Plossl. 




The build quality seems perfectly adequate even though it’s obviously a relatively inexpensive Abbe eyepiece. Especially compared to Takahashi and Ohi built orthoscopics which can cost up to three times as much as the forty quid (£39.60) I paid for this particular eyepiece. The AFOV is a claimed 48° which is a good 6° wider than most Abbe orthoscopics and I suspect the extra field is created by the deployment of a larger field stop than usual for its focal length. As it is purportedly a true Abbe the extra field is probably to aid target acquisition and would be expected to exhibit an amount of lateral edge astigmatism. There is a claimed eye relief of 4.2mm which is 0.15mm longer than a 5mm Ohi Abbe orthoscopic.  




I got first light with the 4.8mm using my 72ED DS Pro. The seeing was a good Antoniadi II~I but the transparency was distinctly below average. The orthoscopic gave a convincing sharp and well contrasted view of Saturn at 87.5x. Saturn was fast approaching transit and I could see a fair bit of detail on the planetary surface and the rings, including the Cassini Division. In fact, I thought the contrast was better than the 6mm Vixen NPL that I directly compared with the 4.8mm ortho’. 




I then turned to Jupiter. The detail was very well contrasted in the equatorial belts with excellent visual acuity. I occasionally witnessed some small amount of chromatic aberration around the planetary limb but it wasn’t particularly bad. I could sometimes detect an amount of scatter near the field stop and even some sporadic ghosting, although again, it wasn’t really a problem. Europa was right next to the limb and about to transit. I observed it once it was past the limb itself and could still see the moon above the surface of the gas giant for several minutes . 




Meanwhile the already poor transparency was getting worse. I decided to split some doubles while I could still locate any before the steadily encroaching cloud enshrouded them. The extra 6° of field helped me find Iota Cassiopeiae more easily, but it took a 2x Barlow to properly reveal all three stars of the system at 175x. The stars were all well defined and their individual colours were easily perceived. The expected lateral astigmatism was basically undetectable when using the Barlow. But even without the Barlow it didn’t seem particularly problematic and was far closer to the field stop than I expected. I split a few more doubles at 87.5x including the Double Double, Struve 2470/74, Albireo and Almach. I could also quite distinctly see the Ring Nebula, albeit often using averted vision. Eventually I turned back towards Jupiter and could make out the GRS pretty easily at 87.5x. 




Apparently orthroscopic eyepieces are expensive because it is costly to properly and accurately cement the triplet part of the element. The use of an inexpensive housing may be a way to keep the overall unit cost down.

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1 hour ago, Stephen Waldee said:


I very much like orthos but at present only have two: Baader 6 and 10.  I am of an age where the Ploessl was considered "very wide field" and the Erfle "so wide you fall into the eyepiece, not a pleasant experience." The ortho was 'standard' and everybody had aspirations to step UP to them from their Ramsdens...


Your review piqued my curiosity.  For some years I used a 5 mm Ramsden even in my C-11 - pause now for gagging and retching - for ONE purpose: it had SUCH a bright view that I used it when looking for incredibly faint photographic 16th mag PGC's or 1 arcsecond diameter planetaries.  It blew away the comfortable 5 mm Hyperion...but was absolutely *painful* to employ.  Later, after my fill of this masochism, I came to my senses and obtained a TMB in that focal length (but that Ramsden was NOT thrown away!)


I had purchased a Vixen 4 mm PL for highest power in one of my scopes...but discovered that there is a raised ring, part of the design of the molded top, that is nearly 2 mm in height, all around the top periphery of the unit.  I cannot get my eyeball close enough to see the *claimed* 50d AFOV.  Maybe 30d is visible at a glance straight-on.  One has to crane one's head and 'look at the edge' and move all around the circle to get a *glimpse* of the edge of field.  Ridiculous!  The alleged 'solution' as it were, is to use a grinder and remove the elevated ring!  (Then maybe one could see 40d of the actual 50d available.) I wish they had made it like the volcano-top Japanese orthos I used to have, oh sometime back in the 19th century as I dimly recall.  


At least this one does NOT have that kind of top; but it still looks difficult for somebody like me to use.  I observe small exit pupils with no spectacles, at least; but the idea of trying to spend a lot of time enjoying, say, Saturn or Jupiter with an eyepiece like this is no longer viable.  However, *maybe* it's the sort of gadget that might assist, if one has a motorized tracking scope; has the object already nicely centered; and then wishes to amp-up the view for a couple of minutes, perhaps to verify a faint phenomenon not clear in a lower power, "comfortable", ocular.


Steve & Regina, Ivins UT


Vixen 4 mm PL.jpg


I've always had a soft spot for ortho's. 




Ever since I acquired several Astro Hutech (Ohi) a few years ago. 




I'm lucky in the fact that my eyesight allows me to use very small EP's, although I usually use the shortest focal lengths for lunar/planetary observing. The simplicity and precision of the build and design can't really be beaten IMO. That being said, the TMB clones come very close, and the TV DeLites are even closer.




I regularly pull the rubber guard off my 4mm NPL as well. A sander or a hacksaw sounds like a good plan lol.



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19 minutes ago, Stephen Waldee said:


Yes, I immediately removed the outer rubber "eyecup" (which it is not) and by now have discarded it.  


I do have a huge 2 HP cutoff saw (below) which I use for grinding or cutting heavy metal pieces, which would make very quick work of the raised ring about the top periphery.  But it is anything but *delicate* in its operation and would likely make a huge mess with a resulting rough and uneven surface: for to do it RIGHT, the object to be cut has to be held very solidly by clamping; and to hold this small cylindrical eyepiece with required force would then also mess it up beyond repair.  The end result of an ATTEMPT to fix this design error would be a completely ruined eyepiece: no doubt metallic particles would get all over everything and if there was any oily substance around the edge of the eye lens, would become attached.  Cleaning with solvents would possibly result in a seepage, with tiny metal flecks all over one or two lenses, perhaps even between elements.  I can predict a cascade of issues that will result in ONE EYEPIECE BEING THROWN IN THE GARBAGE, not being usable at all.  


So the alternative - just scrunching up as close as possible and seeing only the center of the field, missing the field stop edge, seems preferable! "Fool me once, shame on you" comes into play here; and I've had my share of "fixes" that failed utterly.


The worst one was NOT committed by me personally.  A good friend owned a classic C8 that had, IMO, the BEST optics of any one of that venerable line of instruments I've ever peered into.  I saw Mars, at an opposition, at more than 400x: and it looked more detailed and fantastic than in ANY scope I've used in the past half-century.  It was truly a C8 in a million.


But it shook a bit on the original tripod mount and wedge which were frankly under-designed.  The common suggestion was an electric focuser; so he ordered one.  When it came, it was immediately obvious that this new c.1990 gadget was not intended for the OLD, original C8 focuser knob.  Said knob had at least one grub screw; when that was removed it still would not come off the shaft.  My friend had a "bright idea"! He clamped the knob right at the gray metal surface of the back of the OTA and rigged up something to hold the tube, and the clamp, perfectly steady; got out a hacksaw, and started chomping away. 


"Snap - ZING" went something; and he discovered that the shaft going into the knob had a mysterious inner shaft that seemed as though it had been spring-loaded.  


Now, the C8 would NO LONGER FOCUS, as the complicated assembly was totally wrecked.  HE SOLVED THE PROBLEM: no more focusing shakes! (Also, no focusing...at all.)


He told me this in deepest despair but I never heard about his eventual efforts to try to resurrect the thing from the dead; we never mentioned this again, and finally lost track of each other.  I do not know if he tried to have a factory repair or just gave up.  (This was some years before the inner workings of the C8 focuser assembly were documented on the web with x-ray drawings, so who knew?)


With experiences like this in mind, I tend not to take extreme measures.  


Ergo, when - last year - I accidentally started loosening the wrong peripheral screw around the back of my C-11, to add a small bracket, and realized almost immediately that it was one of those that had a lockwasher and nut rather than being fitted into a threaded hole, I instantly STOPPED.  The other side of the bolt was totally invisible behind the primary but it was obvious by the "feel" that it was one I should not have touched (Celestron is completely at fault here, for they have NEVER, to my knowledge, documented WHICH screws are captive, and which are intended for accessories; and all of them have the identical bolt-head.  I have actually complained to them, and got no meaningful response.) 


Well, I did not go further.  Bolt would not tighten down again; and continuing to unscrew would send a lockwasher and nut into the interior; who knows WHAT damage this might do?


Bolt was still obviously attached to the lockwasher/nut, so I merely wrapped a small length of wire around the exposed threads it to stabilize it.  


To open the C-11 OTA and tighten it again, requiring removal of the corrector plate and then replacement of the tiny wood shims and re-alignment, would cause possibly as much as two days of adjustments, based on previous experience.  I shall wait until one fine day, long into the future, when the corrector plate NEEDS cleaning on the interior side, and not take further chances.  Then, I shall re-tighten this screw, the further collimation chores being a given and necessity anyway.


This same friend, BTW, had a Synta-made Orion-US 127 mm Mak.  It came with a tripod foot that he wanted to remove; he assumed that its bolts were into threaded holes and so simply unscrewed them -- and "BING, tinkle" -- the washers and nuts were now rolling around inside the OTA.  (They were absolutely invisible to him when he peered through the corrector from the outside before trying this.) Again--NO info about this in the PDF manual or any printed sheet with the scope. 


These devices are in effect FRAUGHT WITH PERIL.  Do-it-yourselfers are often let down, because they actually would have designed them BETTER than the factory did, with more proper opportunity for modifications.  If the maker has put some removable screws (into threaded holes) on the back, for attaching finders, and there are ALSO two to four IDENTICAL looking screws (or rather, bolts) near them, WHO is to know which are attached with nuts, and which are removable--if the documentation does NOT mention it, and if the sales person and even phone customer support from the company has no idea how to give proper instructions.


I once wrote to Mike Swanson, the creator of the infinitely useful site "NexStarSite.com" and asked if he might put in a page about the removable, versus non-removal, 'accessory' screws on the backs of SCTs and Maks.  He did not feel it was necessary because he felt the info WAS available from Celestron; suggested I go to their help pages online and type in simply the word "screws".  I did so--and at the time (maybe it's changed by now) got an article that warned about undoing the wrong ones and merely said "peer into the scope from the front and see which ones are held by nuts".  


Problem is: in a number of scopes I have had, usually these things are NOT directly visible from peering into the corrector from the outside, even using a VERY powerful illuminating torch.  I of course did this on the C-11 in the incident above: NONE of the screws on the back (or, rather the nuts mating them) were visible.  


Again: discretion is called for and now I AM PARANOID about this stuff; and unlike you, I do not particularly like to dismantle things and poke around to figure out the mysteries inside them!




Steve & Regina, Ivins UT



Well, when I said I like to dismantle stuff; I meant not expensive stuff. 




The dovetail on my 102mm (Synta) Mak was just held in with a couple of Phillips screws.




I turned it 180° so that the dimples would match up with a Vixen-style mount bolt like my 90mm Orion StarMax.



Edited by Nightspore
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