Konus-Synta achromat refiguring. Help!!

Hi everybody!

I have a Konus 5" f8.3 with not a sharp optics, in focus stars has
many bright rings...with green filter as well.
So I decided to experiment with the shims. The difficulty
is not only the under correction but with a "s" zone ~70%
Well the original shim is ~0.4mm. Changed it to 0.1mm I not
achieved anything....
Then I asked a friend to help measure the radii on the 4 surfaces.
Put the numbers in OSLO and I got overcorrection using BK7-F2 glasses.
Am I missing something or the glass has a irregularity that creating
the under correction?
If I can get the correct glass info I may decide to refigure one of
the surface... Pheraps R4 edge? Please dont tell me it is impossible,
I hapy
to lose the coating just to make the lens sharp at least in green!
R1=611.873mm
R2=353.286mm
R3=355.631mm
R4=1488.956mm
Any help, suggestion appreciated!
Thanks, Miki.