I believe it has to do with F-ratio and size of the central obstruction. The larger central obstruction the more light is distributed from the airy disk to the first diffraction ring. Faster newts tend to have lager secondary mirrors compared to slower.
Scopes: Stellarvue: SV102 ED F7; Celestron: 9.25" EdgeHD F10, 8" SCT F10, 6" SCT F10, Omni XLT 150R Achro F5, Onyx 80ED F6.3; Meade: 80ST Achro F5.
Mounts: ES: Twilight I; Bresser: EXOS2; SW: SkyTee2, AzGTi; UA: MicroStar.
Binos: Orion: Little Giant II 15x70, WorldView 10x50, Nikon: Action EX 16x50 & 8x40.
EPs: Pentax: XWs & XFs; TeleVue: Delites, Panoptic & Plossls; ES: 68s; Vixen: SLVs; Baader: BCOs, Aspherics, Mark IV; Russell Optics: SuperPlossls.
Diagonals: Baader: BBHS silver mirror, Zeiss Spec T2 prism, Clicklock dielectric; TeleVue: Evebrite dielectric; AltairAstro: Positive lock prism.
Filters: Lumicon: DeepSky, UHC, OIII, H-beta; Baader: Moon & SkyGlow, Contrast Booster, UHC-S; Astronomik: UHC, Orion: UltraBlock, SkyGlow.
Observing: DSOs: 2147 (Completed: Messier, Herschel 1, 2, 3. In progress: H2,500: 1674, S110: 77). Doubles: 1441, Comets: 18, Asteroids: 95