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The illustration you show, doesn't give the necessary detail on an AIR SPACED achromatic doublet.
On my ST80 there are three small aluminium tags which separate the front element from the rear in the objective.
So, these two pieces of glass must be:
-Front element facing the correct way ( the curves may look similar but could be different!)
-Have the correct spacing between them
and be in the correct radial alignment to each other.
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