Per a request, here are some basic steps to follow when upgrading
1) The original ZS80 cell is reached by first fully retracting the
-There is a small plastic ring at the tip of the dew shield, which
acts as a retraction stop.
-Carefully grasp the plastic ring, with finger tips on the inside
of the dewshield if needed.
-With the retraction stop removed, the dewshield can be retracted
as far as possible, until it bottoms out on the OD step of the OTA.
2) The original doublet cell should be clearly visible, as should
the end of the OTA that the cell is threaded into:
-Carefully grasp the outside of the cell, and begin to unscrew the
-The original cell should come out, and you will see that the cone
baffle is attached to the cell.
-Pull out the cell baffle assembly, and lay the OTA aside.
3) The cone baffle acts as a retaining ring for the original
doublet, so be careful when unthreading, as not to drop the original
-Grasp the baffle/cell assembly, with the baffle pointing straight
-Unscrew the cone baffle from the original cell, and carefully set
the cell aside: warning: the original objective is loose in the
cell, be careful!
4) Carefully screw the cone baffle into the new objective cell.
-Rethread the baffle onto the new APO cell, careful not to
5) Reverse the order of step #2 with the new APO cell and baffle
6) Reverse the order of step #1 to reattach the dew shield retention
7) Pray for clear skies.
As for vignetting, the only brief check I performed was verification
that I could see a very little bit of the new APO cell at the front
of the new doublet, by looking through the focus tube fully
retracted and fully extended. It was close, but I could see either
the cell or the tip of a finge held over the edge of the APO
objective in either case: effectively no vignetting based upon this
Hope that this helps, and enjoy your new 80mm APO flourite doublet!!