in the directions to assemble the high resolution optics, it is noted:
**Step 2: Insert the tube lens**
Place the lens tool on a steady surface
Place the 12.7 mm achromatic lens on the lens tool
**Check the lens has the more curved side facing down**
Take the optics module and place carefully over lens
Push down hard to seat the lens in the optics module
Isn’t curved side facing down a step for the PMMA condenser lens and not the achromatic lens?
my achromatic lens is concave on both sides?
The achromatic lens is likely to be curved outwards on both sides, but usually not symmetrical. The instructions say the ‘more curved’ side.
As ever @WilliamW beats me to it and is exactly right - if you get a particularly nice lens, it may even come with a marking, or a note in the datasheet, that explains which side should face the focus and which should face the collimated beam. In that case, the camera should be on the focus side, and the objective on the collimated side. Usually, the less curved side should face the focus - so the more highly curved side should be face down on the tool.
Thank you both @williamw and @r.w.bowman .