Getting out the Christmas tree in the attic I knocked over an old camera bag
and out fell a set of close up filters 1x, 2x, 3x, and 5X. Sometimes called dioptre lenses
These were very useful in the old days when I had no tubes or macro facility
they could be used individually or screwed together to make up to 10x .
No exposure correction required and a step down ring allowed use with more than one lense they start around £10 and go up for multicoating £25