Ruan,
Just to check, did you try this by rucking out the draw tube, and if not enough out then pulling out the eyepiece? Worth a try just out of curiosity as I've never heard of a refractor not having enough in-focus. I also have a 4" f/5 refractor, and if you don't have a diagonal the draw tube needs to be rucked out a lot more to achieve focus, not in-travel, with an eyepiece. I know what you mean about the Moon getting "smaller", but the draw tube needs to be pulled out. Karl mentions an extension tube just for this purpose. A barlow with the lens removed does the same job.
Alex.
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