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Thanks Marc. Got it I think:
A Celestron C9.25 has a glass cover, but it's not a lens. It bounces the light around until coming out the end. I don't use a coma corrector or field flattener - therefore I have no refracting elements.
If I added a field flattener to the C9.25, it would then have a refracting element.
Whereas the William Optics GT-81 is a tripplet refractor with two field flatteners inside the scope, so it would most definitely have refracting elements.
Is that correct?
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