Ken, thanks, I understood what you said and how T adaptors work, and I have ordered it from Bintel. I was just curious about the advertising for the speciality one piece wide mouth adaptors like this one
http://www.ebay.com.au/itm/Telescope...p2054897.l4275
that seem to offer larger aperture carry into the camera than the standard t thread system. Perhaps it's just marketing hype as I am sure people here would know about it if there was any real benefit.