By: Vlad Fedosov
The plossl eyepiece design is a staple of the telescope world. With a FOV of 50°, these eyepieces are definitely not a wide-field, but what they lack in FOV, they generally make up for in an uncompromising crisp image. The 55mm Televue plossl is perhaps the most exotic and uncommon in the line being the only 2″ variant as well as a monster in size compared to its 1.25″ shorter focal length variants. The 55mm Plossl has an eye relief of 38mm and weights in at 1.13lb.
I had the 55mm TeleVue plossl out for a night of observing in mid-October during a partial moon under my mag 4 suburban sky. The telescope used was my C8 XLT with a 2″ dielectric diagonal. Seeing and transparency were average that night.
My first look through the eyepieces was at a random starfield. My initial impression was that I was not looking at anything, but then I would get a glimpse of a star or two. I soon realized that the issue was the long eye relief of the 55mm makes for a very odd and critical eye placement. I did get used to the correct position and it became better, but it was still among the hardest eye placments that I have experienced through any eyepieces. The good news is that the view at 36x was very pleasing. Bade I say that the c8 produced a refractor like image with this eyepiece(no doubt a lot having to do with the low magnification).
After scanning around the milky way it was onto the moon. Here is where I discovered an even more serious issue then the critical eye placement. The long focal length of the eyepiece produces a secondary shadow that is quite noticable on the moon. I don’t believe that I have ever experienced this with any other eyepiece, but I also have never used another eyepiece in this focal length range.
Now I do not want to sound like I’m trying to bash on this eyepiece, as I believe that any plossl in this focal length will have these inherent issues. I guess at this point you might be wondering that with these issues why someone would an eyepiece in this rather extreme focal length anyhow? Well, the simple answer is; exit pupil. If you have a fairly slow scope and you want to maximize your chances of spotting some very large low surface brightness nebula of other DSO from a truly dark sky you may want to have an exit pupil that approaches that of the max your eye will dilate to. With my c8 I can achieve an exit pupil of 5.5. Not quite as large as my eye will dilate to but close to it. Again keep in mind that this would not work if you are not under a dark sky.
One other aspect of this eyepiece that I can’t quite overlook given TeleVue’s excellent reputation is the rather large threaded lens barrel that is not darkened at all. I expect this from a cheap knokoff, but not a TeleVue. This will definitely produce glare if there are any bright stars, the moon, or planet near the edge of the FOV.
If you get the impression that this was not one of my favorite eyepieces that I have owned, then you would be correct. I had high hopes for this eyepiece as one that I could use to easily scan around the milky way but the issues mentioned above were bothersome enough to turn me away. I do not think that this is a bad eyepiece at all, but if you are considering it I would consider the issues mentioned above and decide on whether they will bother you or not.
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