please help!

As much as I know we have to use subjunctive on the latter clause with “only if”, about this sentence: “From this distance, only if you use a pair of binoculars can you/ are you able to see them clearly”
This sentence seems a bit weird for me, is it grammatically correct? How can we express it in another way?

Welcome to English-test, CrownKyu.

Your sentence is fine. ‘Only if’ does not require subjunctive. It is a mistaken rule.

Only if he studies can he pass the exam.
Only if the studied could he pass the exam.
Only if he were smart could he pass the exam.

Only the last sentence contains a subjunctive verb (in bold).