Learn Portuguese (Portugal): Esta miniatura é difícil de ver sem a lupa. - This miniature is difficult to see without the magnifying glass.

In Portuguese, when an adjective describes how hard it is to do something to a specific subject (like esta miniatura), we must link that adjective to the infinitive verb using the preposition de. This happens with evaluative adjectives like difícil, fácil, and impossível.

Could I phrase this without making esta miniatura the subject?

Yes, you could say É difícil ver esta miniatura sem a lupa (It is difficult to see this miniature...). Notice that in that version, the de disappears. The de is only required when you move the object to the front of the sentence to become the subject.

If the subject is feminine (Esta miniatura), does the adjective need to change?

The adjective in this structure must agree with the subject in gender and number. Here, difícil is a neutral adjective that ends in -l, so it is the same for both masculine and feminine. But if you used a word like complicado (complicated), it would have to change to feminine: Esta miniatura é complicada de ver.

Why does the sentence use a lupa (the magnifying glass) instead of just saying sem lupa (without a magnifying glass)?