I don't get it, what are Rog, Dannig et. al. for?

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Irin77#4248 wrote:

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vestolevs#5239 wrote:

Expedition is one of the most important game mechanics to farm and modify top gear and currency. The expedition boss drops one of the most imporant jewels and flask. Easy to get high tier items on high level logbooks, easy to get high tier affix items from the expedition npcs, easy to recombine high tier gear obtained from these. If you know what you are doing, that is...

Yea but expedition logbook drops are very rare. Where is the best place to farm them?