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Unknown Orthos

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I picked up this set of strange “Orthos” and wonder if anyone might know anything about them or seen similar?


They appear to have originally been microscope eps with the 20x, 30x, 40x, 50x designations (meaning 12.5, 8.33, 6.25, 5mm fl) that have been converted to 1.25” barrels.


Comparing them to CZJ Abbe orthos they have similar narrow AFOV but are brighter and have very sharp field stops. Also interestingly the eye lenses are larger than the corresponding CZJ eps.


They give a bright, sharp and very cool image that reminds me of the cool rendition the BCO 10mm gives (which I didn’t like at first but do now) and they are ortho in that there is no noticeable distortion (unlike a plossl) There’s no sign of CA. They’re pretty decent actually.  Can’t really open them easily to see the lens arrangement as the barrels are glued in place and the glass deeply recessed within.

So, what are they? 🤔


Edit: I was wrong thinking they were microscope eps- obvious really as they aren’t standard microscope multipliers. They’re spotting scope eps so no idea what fl they are- must depend on what scope they were designed to be used in.   

Edit 2: they look very similar to the eyepieces on this vintage Parks 60mm spotting scope


Edited by markse68
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11 minutes ago, Louis D said:

Perhaps a variation on the Bushnell Spacemaster II spotting scope eyepieces?

yes they do look similar too apart from the position of the engraving. Surprisingly modern looking. They seem to be very nice quality with nice looking coatings. Probably Japanese I guess. Now I just have to work out the focal lengths- will have to do it by comparison to known fl orthos as there’s not much chance of finding the focal length of an unknown vintage spotting scope!


Edited by markse68
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I'd assume it's 400mm for a start, and that makes your eyepieces 20mm, 13.3mm, 10mm, and 8mm going from 20x to 50x.  Judging by the sizes of the eye lenses relative to known ortho eyepieces, I'd say those numbers aren't too far off.

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21 hours ago, Louis D said:

I'd assume it's 400mm for a start

I think your assumption was pretty good Louis- using my very accurate “counting windows in distant office block” technique I compared them to a 25,16 and 6mm ortho. The 25mm framed 14 windows, the 20x 12, the 16mm 10, the 30x 8 and so on. So I reckon the 20x must be about 20mm etc 👍


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