The retinal image is inherently blurred, yet the world typically appears in focus. I will review the role of neural adaptation in adjusting to image blur. Brief exposures to blurred or sharpened images can strongly bias the stimulus that appears best focused. These adjustments have a large influence on subjective image quality but comparatively weaker effects on acuity, suggesting that they function primarily to maintain perceptual constancy despite changes in the environment or the observer. The adaptation may be important for compensating for optical errors, but probably reflects more general processes that match visual sensitivity to the visual environment. For example, similar adjustments occur for temporal blur, suggesting that the adaptation calibrates perceived focus of both space and time.