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Whilst it's a big eyepiece by normal standards there have been plenty bigger over the years.
The Siebert Observatory series have 4" barrels.
Attached is an image of a 4" barrell 80mm Siebert eyepiece alongside a 40mm Pentax XL, which itself is no midget.
Also attached is an image of the 60mm Pentax XL eyepiece which has a special threaded barrel. The 60mm Pentax XL is pictured alongside a 22mm Televue Nagler T4 on the right, again not huge but not a midget.
The 60mm Pentax XL is 10" long and 4" in diameter. It was available by special order in the late 1990's and early 2000's. It sold for $US 3,995. It was designed specifically for use with the large Pentax refractors, which didnt see much light in the Western World.
Cheers,
John B
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