Something like this? How to Invent Everything: A Survival Guide for the Stranded Time Traveler [https://www.amazon.com/How-Invent-Everything-Survival-Strand...]

Hope a website will work, assuming your trip is not too imminent :)

https://simplifier.neocities.org/index.html

Careful, come back with too much knowledge / science and the catholic church will have you killed.

I think as long as you kept your mouth shut about doctrinal matters, you'd be fine. Almost all of the scientists who go in trouble with the church were busy writing commentary on religious doctrine outside of their scientific work, and that's what got them in trouble generally speaking. The Catholic Church for its faults funded a lot of astronomers and other scientists in the medieval period and into the Renaissance.

Yeah idk. Lenses are hard.

It's not the lenses which are difficult, it's clear glass.

With a piece of pure glass, the rest is some emory and a great deal of patience.

Clear glass is also more about knowhow than raw technical difficulty, it isn't the Bessemer process, it's knowing how to flux with soda + add some lead to get the melting point down, then pouring it on lead to get nice flat sheets.

It’s not like you’d be distracted by Twitter, just knowing how it works you could probably work it out with a few skilled glass makers.