I've read a lot around this site that an ideal quality of the lens is achieved when using f-stop roughly 2 stops slower than the fastest value of the lens.

Firstly, I'm not exactly sure what "2 stops" mean when it comes to f-stop, but this isn't really important in what I'm about to ask. What I'd like to know is what is the base f-stop when counting this value.

Let's look at it this way: If I have a prime lens with f/1.8, then obviously I'll be getting the ideal value from f/1.8, let's say after 2 stops I get f/2.8?

But! What in case of zoom lenses, for example 18-55, which have f-stop f/3.5 - f/5.6. Should I take f/5.6 as my base value, or does the base value depends on the real fastest value at the exact focal length?

Therefore, if I set the lens to 18 mm, their fastest aperture is f/3.5 and thus the ideal quality is at f/5.6 and when I set it to 55 mm, their fastest aperture is f/5.6 and thus the ideal quality is at f/8 ? Or is it f/8 for the whole focal range ?


Question: Is a password easier to brute force if it contains a repeating pattern?
Answer: There are three scenarios here:

Attacker has no knowledge of the pattern scheme:
When the attacker has no knowledge of the patterns, the brute-force attempt will have to be exhaustive. The attacker gains no practical efficiency improvement, because there is no way of him knowing the construction of the password.

Attacker has some or full knowledge of the pattern scheme:
If the attacker has knowledge of the patterns, they may improve the efficiency of their bruteforce attack by not attempting passwords that do not match the pattern scheme.

Attacker has no initial knowledge of the pattern scheme, and multiple hashes are available:
If the attacker has no initial knowledge of the pattern, but has a number of different password hashes to crack (all of which use the same scheme for the password) he may crack a small number of them via exhaustive bruteforce, then deduce the pattern. From there, the attack becomes much more efficient.