Learn Italian: Avevo inquadrato il paesaggio e tutto era nitido. - I had framed the landscape and everything was sharp.

Avevo inquadrato is in the trapassato prossimo (pluperfect). You form it by taking the imperfect tense of the helper verb (here, avere becomes avevo) and adding the past participle of your main verb (inquadrare becomes inquadrato). It translates to "I had framed".

Why do we use the trapassato prossimo (avevo inquadrato) in the first half, but the imperfect (era) in the second half?

The trapassato prossimo is used for an action that happened before another past situation. First, you framed the shot (avevo inquadrato). Then, at that moment in the past, the landscape was sharp (era nitido). We use the imperfect (era) for the second part because it describes a continuing state in the past, rather than a completed action.

Does inquadrato only mean "framed" like a wooden picture frame on a wall?

Not just physical picture frames! Inquadrare is heavily used in photography and film to mean framing a shot through the viewfinder or lens. Given the word nitido (sharp or in focus), this sentence is definitely about setting up a camera shot.

Is nitido only used for camera focus?