I have used them since Televue introduced them. They work great. They fit most of the Televue models, some requiring adapters, and will also work with some competitor eyepieces as well.
As for 4.0 diopters, I would give Al a call. He would be the one to speak to regarding your situation.
There is only one constant in our infinite universe; it is change.
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Losmandy Titan 50 GEQ, G11, AP800, Denk BVs, 7x50 Fujinons, 10x50 Nikons, 15x70 Astrophysics,
16x70 Fujinons, 22x100 Oberwerks, Sim Picheloup CPT, Canon 40D, 60Da, Vixen Polarie, SXV-H9,
DMK 41AU02, DBK 21AU618, Shelyak Lhires Lite Spectroscope
Vice President, City Lights Astronomical Society for Students (CLASS)
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