It's kind of fun monitoring the Bitcoin network and seeing what hash got the blocks...makes me wonder, what's the BIGGEST or HIGHEST difficulty ever hashed by a miner? Is there any way to figure that out?

For example:
Block 751848 hash "00000000000000000002f03ad7a1dd69628c4747ea8751dc9a5497fd451a3667"
Block 751849 hash "00000000000000000000bdaaf8190000aac4323bd941d1095deffc36295f6512"

Also, how does one calculate the difficulty level of any particular submitted hash? i.e. What's the calculation relating the number of leading zeroes of a hash and the difficulty level of the hash?
(I've tried reading up on it and just haven't found a clear answer)

Thanks in advance and so sorry if it's a simple answer!