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Orion Expanse (re-visited)


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I obtained my first Orion Expanse eyepiece in 2016. The 9mm is supposedly the best of the range so that was the one I initially purchased. I’m fairly certain these were originally manufactured by Barsta/BST. The series has been marketed under a variety of brand names. As far as I know they are all more or less the same apart from the branding and housing finishes. There have been rumours that the T.S. Optics versions have better coatings, but I can’t substantiate this.  There are four in this range of fairly lightweight 66° field eyepieces: 6mm, 9mm, 15mm and 20mm. The 6 and 9mm have Smyth-type barrel lenses while the 15mm and 20mm do not. My Orion 6 and 9mm have 22mm chromed brass barrels featuring an undercut. At 75mm the 6mm is 5mm taller than the 9mm eyepiece.




Both have 20mm eye lenses with the 6mm having an 8mm field stop compared to a 15mm stop in the 9mm. Orion Telescopes & Binoculars claim around a 15mm eye relief for both the 6mm and 9mm Expanse. Which I think is a tad optimistic.




I acquired the 6mm quite recently. Although just over three years ago I bought a generic 15mm ‘UltraWide’ which is to all intents and purposes a 15mm Expanse.




The UltraWide had a black aluminium flared barrel. My plan was to use it with a light ‘grab and go’ modified ST80 set-up. Unfortunately it exhibited a lot of lateral astigmatism at f/5 that could only be just about ameliorated with a Barlow.




As it was primarily intended for rich field observing this wasn’t really an option. I wouldn’t particularly recommend the 15 and 20mm versions with anything less than an f/8 focal ratio. 




One aspect that I did like about the 15mm was that there were no eye placement issues. The 9 and 6mm can noticeably ‘kidney bean’ if the eye position isn’t quite right. I never thought the 15mm was quite as sharp or as contrasted as the 9mm either. Eye placement issues aside, the 9mm is bright, very sharp across the field and well contrasted. Colour separation is excellent and it is just as good on planetary targets as open clusters. 




It can have a tendency to ghost on particularly bright targets such as the Moon, especially if coupled with a Barlow. The 6mm Expanse is basically as good as the 9mm in my opinion. Although in my experience it can have a tendency to ghost slightly more than the 9mm version. Both Expanse eyepieces can suffer this fault primarily with lunar viewing, although having said that I have had pretty decent ghost-free views of the Moon with both of these eyepieces when used without a Barlow. 




There are some interesting build differences between my new 6mm and older 9mm Expanse EP’s. They are only trivial but may be indicative of different manufacturers. The Barsta site appears to have disappeared from the internet so I have no idea if they still commission products. The Expanse roll-up rubber eyeguards look identical at first glance. However, the newer 6mm Expanse eyeguard consists of a softer rubber reminiscent of the old GSO roll-up guards. These are distinctly different in feel to the eyeguard on the 9mm Barsta made Expanse.




The older 9mm eyepiece has a typical Barsta/BST stiffer guard. The end caps on the 6mm are not traditionally like Orion dust caps. The embossed ‘Orion’ logo isn’t present on the 6mm and the field lens dust cap doesn’t have the number ‘317’ on it like most of my other Orion eyepieces. Although this may be due to present day supply problems. The distinct coloured band or collar at the top of the housing of each eyepiece are slightly different hues of blue. 




At the end of the day these eyepieces are quite reasonably priced for the performance they deliver. Compared to a lot of more modern offerings they are possibly a little antiquated. The two shortest focal lengths have some eye placement issues and the 15 and 20mm will show lateral astigmatism in faster focal ratio scopes. The advantages with these eyepieces are that they are light and relatively small with a capacious 66° field of view. I particularly like the 6 and 9mm for deep sky. As they are relatively compact, and easily carried in a pocket, mine get a fair bit of use. 

Edited by Nightspore
Gremlins with attitude
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