Yes, call me crazy... I have modified my Aspectem Vario and replaced the zoom eyepieces with TeleVue 24mm Panoptics making them an excellent fixed magnification 20.8x80.
Probably the first question you are wondering is why?
Well, after the novelty of the Vario it wore off, the small FoV and lack of eye relief starting to distract from my enjoyment. I thought about selling it a few times but sharpness and clarity of the views it provided simply did not let me take that step.
What I felt I needed was a 20x80 (or 20x100) with at least a 3° FoV to compliment my 40x80 UWA. Of course it needed to be able to hold its own against the UWA which, as you can imagine, is not an easy task. I looked at the current offerings and, although many are quite good, they simply did not hold up to the standard set by the Aspectem. This is not surprising considering they cost 4 times the most expensive 20x100 currently available.
Looking at the construction of the Aspectem I realised that the original eyepieces could easily be removed, revealing the M52x1 thread used to mount them. The focal plane is actually about 16mm above that thread so I thought there might be a chance that a standard telescope eyepiece could be adapted to work with them. The journey started with finding an eyepiece that harmonised well with the objectives and would come into focus given the physical space available. As many know, the vast majority of wide angle, well corrected eyepieces have field correctors in front of the focal plane. These unfortunately would not work due to the prism construction and eyepiece in-focus requirements. Looking at the design and specifications of almost every 24-26mm eyepiece out there, It turned out that, in theory, two eyepieces could meet my quality expectations and FoV requirements while providing for a technically feasible implementation: the Televue 24mm Panoptic and Explorer Scientific 68° 24mm.
The second problem was figuring out how to focus. Most 1.25” helicoid focusers made for telescopes are too long for this purpose and 2” focusers are two wide. For almost a year I pondered ways of making my own helicoid using 3D printing but could not come up with a suitable solution. Then one day I stumbled upon an M42 15-26 Helicoid camera lens adapter used for macro photography... It occurred to me that with a little modification, they might be the solution I was looking for.
I then tested the ES 68° 24mm and, although on-axis sharpness was quite good, edge sharpness was only average… I think it is obvious that this project was not about being average ... So I ordered a pair of 24mm Panoptics to test. My first views with the prototype where very encouraging. Excellent center sharpness and edge correction.
The rest was a matter of building an adapter/focuser that allows 24mm Panoptics to be used in place of the original eyepieces. What I came up with is an M52x1(F) —> M42x1(M) adapter, the helicoid focuser mentioned above, and some 3D printed parts to make it all work together. Unfortunately I did not realize that I forgot to to take pictures of the individual parts until everything was assembled… Mia culpa.
Luckily, I do have the 3D CAD renderings which actually give a better understanding of the parts and how they interact. As you can see, the construction is actually pretty simple. The black components are pre-made and the red, yellow and blue components are what I had printed (Shapeways).
The focusers are non-rotating so the winged eyecups actually stay in the position they are.
I should note that neither the binocular, nor the eyepieces needed to be modified, other then removing the original eyepieces. It takes about 2 minutes to switch back to the original eyepieces and about 15 minutes to remove the Panoptics from the helicoid adapter (They have to be gently heated).
In my opinion, the result is indeed “the best 20x80 money can buy”… Ok, its actually a 20.8x80 and the claim might be a little steep but until someone shows me something better, I’ll stand by it
Center sharpness is excellent and stars remain pinpoints of light to the edge of the FoV. Upon deliberate and close inspection of Lyra, I could see it starts to a develop slight spikes in the outer 10% but still maintained a stellar core. Maybe not quite as good as my Swarovski EL but I would still consider them “sharp to the edge”. Transmission is excellent, actually better then with the original eyepieces due to fewer glass/air surfaces. Color rendition is on the cooler side in comparison to original Vario eyepieces which I find to be very warm. Of course being Panoptics, these are not orthoscopic. When viewing the roofs of distant houses, slight pincushion distortion is noticeable. It is actually slightly less then the distortion present in the Vario eyepieces and I don’t find it uncomfortable or distractive.
The only negative point I can find is a very slight vignetting that makes the field stop a little fuzzy. The FoV checks out to be little over 3.1° using Navi and Achrid in Cassiopeia. Their separation according to SkySafari is 3.1° and both are simultaneously visible at the field stop. This is actually slightly better then what calculations based on the field stop diameter says it should be (3.08°). The noticeable vignetting starts literally right at the field stop. I suspect that if I where to reduce the field stop from 27mm to 26.8mm it would probably not be noticeable at all.
And now one last bit for bonus points… I can also use UHC filters with these
Unfortunately due to the weather lately I have not been able to get these under some dark skies. The forecast for the next 10 days does not look promising so I will post my observing impressions once the weather gods decide to have mercy on me.
Edited by Mad Matt, 14 June 2018 - 10:11 AM.