As the title says, I have an older Celestron Newtonian, a C-8N which like most C8N's is a 200mm / 1000mm f5. This one however is considerably shorter than a conventional C8N and it measures around 50cm (20") in length. I do happen to have a standard C8N to compare it to which measures around 92cm (3') in length. This short tube version has been sat on a shelf for about a year, I bought it with some other astro kit which was connected to an ebay auction winning bid. I just assumed that someone had cut it down in a failed experiment but today whilst sorting out some old scopes to sell on, I tried looking through it (albeit terrestrially) for the first time with a 24mm EP and the image was perfectly sharp, in fact it was incredibly good. Anyhow, when I looked at it further I noticed there is a small lens in front of the secondary mirror, obviously doing some form of optical correction for the shorter length.
The scope is a David Hines delivery so I know it had a little more love on its dispatch than the usual scope vendors of that era.
I've not seen anything like this before and can't find anything online about it. Any ideas what this is? I've taken a picture of it as best I can, you can make out the lens holder and the glass lens in the middle of the image.