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Peter, the hardcap has a smaller hole offset to one side that has a second removable cap. The idea is that you can use this to reduce your aperture for very bright objects, such as the sun and the moon. So instead of using a 20cm aperture you just remove the smaller offset cap and you get 8cm instead. Its a nice size to fit a small sunfilter too, and in theory you can use it to cut down the brightness of a full moon. This is common feature of Skywatcher telescopes, has been for years - even the refractor aperture caps have them. Occasionally we meet newbies who don't realise the full hard cap comes off and have just been using the smaller offset hole and wondering why they can't see much!
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