Mark1, thanks for the reply.

I'm not sure what you mean by 'outer rings'; my scope has conical knobs with slotted screws in the center. Do you mean I should loosen the slotted screws, then turn the conical knobs to adjust and re-tighten the screws? What do you mean by the 'inner adjustment' that I should not move?

I tried loosening the slotted screws but the conical knobs did not turn with finger pressure.

Thanks