Search:

I have used a 30x, but the depth of field is so small that you have to be right on top of the blade, usually blocking out the available light and risking nicking your nose if you wobble a bit...!
...

I use a Belomo 10x triplet for much the same reason as Glen. The 10x has a nice wide triplet lens that lets more light through than higher magnifications. It's an excellent brand - as good as if...