not believe (your) (own) eyes

to think that something you see is not likely to be real.

She looked so different in a uniform, I couldn't believe my eyes.

Usage notes: sometimes scarcely or hardly are used instead of not:

When he found the ring in the grass, he could scarcely believe his eyes.

• burst onto the scene
• burst out
• burst out doing something
• burst out of
• burst out of somewhere
• burst someone's bubble
• burst the bubble
• bury head in the sand
• bury the hatchet
• bury your head in the sand
• bush league
• bush telegraph
• business as usual
• business end
• business end of
• business end of something
• business is business
• busman's holiday
• bust a blood vessel
• bust a gut
• bust a gut laughing
• bust ass
• bust balls
• bust your ass
• bust your balls