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Hi Mimo,
The inside diameter of the baffle tube upon which the SCT mirror slides, is 1.5" for 8" aperture for Meade and Celestron SCT's. The 10" and larger aperture SCT's have baffle tubes of 2" inside diameter.
The idea of the "eyeopener" type adapter , is to retain the 2" aperture at the back of the tube. Meade and Celestron have always supplied 1.5" aperture, visual back adapters for all their SCT's as standard. This results in vignetting which can be noticed in the 10" and larger SCT's, if using eyepieces with a field stop greater than 1.5". There is no benefit to be gained by usning a thing like this on an 8" SCT.
Hope this helps, Mark
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