Here are two pictures taken with a TAL 200k and Hutech focal reducer.
About 700k each.
http://users.bigpond.net.au/avandonk/CentA_FR.jpg
http://users.bigpond.net.au/avandonk/OC_FR.jpg
The focal reducer seems to work best with thin spacer (for 640mm FL) with the Tal 200k for flattening the field. The resultant focal reduction is a factor of 0.895.So resuting FOV is 1.15X0.77 degrees and focal length of 1790mm @ F9.
Details Cent.A 6X240sec
Omega C. 3X240sec
For both,Canon 5DH,ISO 1600,in camera noise reduction on,LPR filter,raw to 16b tiff,stacked with Registar,adjusted curves and levels in Photoshop.
There is also a pic at the same scale of HH and Flame only a single two minute exposure all else the same, before the cloud won again.
Bert