Hi all, a few weeks ago I received my Celestron Edge HD 800 as an upgrade for my (old) INTES MK69. I also bought the 0.7 reducer. This setup will be used in combination with my ZWO ASI071MC Pro. Since the weather is really terrible the last couple of weeks I didn't get the opportunity to test this setup so far, but in the few hours that I did I noticed that I couldn't get the back focus right with the 0.7 reducer. According to the Celestron specifications the back focus should be 105mm... but that didn't work at all. I tried to get the back focus on the right spot with several spacers without any succes. Therefor I decided to ask Celestron if the 105mm backfocus in combination with the reducer could be wrong... and this was there answer:
Thank you for contacting Celestron Technical Support.
There has been some confusion about the reducer's back focus. The 105mm figure is for the .63X NON-egde HD reducer for the classic SCT telescopes.
The back focus for the .7X reducers on the Edge HD telescopes does not change from the telescope's native back focus without the reducer.
The back focus with the reducer on your 8 Edge HD will be 133.35mm as measured from the back flat flange on the rear of the reducer.
If the Edge HD focal reducer star coma tails point inward, the back focus is too close, if the coma tails point outward the back focus is too far out.
I guess this can be helpfull for other users that are struggeling with the same problem....