十万个为什么·科学启蒙30篇（4）

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为什么望远镜需要调焦

Light from distant stars travels in nearly parallel rays, but lenses or mirrors bend them to converge at one point.
If the focal plane doesn’t align exactly with the camera sensor or your retina, the image appears blurry.
Small manufacturing imperfections in optics mean each telescope needs fine-tuning for sharp focus.
Temperature changes cause metal parts to expand or contract, shifting lens positions slightly over time.
Different wavelengths of light focus at slightly different distances, requiring chromatic correction during focusing.
Astronomers adjust focus manually or automatically before every observation to maximize clarity.
Planetary imaging needs tighter focus than wide-field nebula shots due to object size and contrast.
Digital sensors have pixel sizes that demand precise alignment to avoid resolution loss.
Some telescopes use motorized focusers guided by star-sharpness algorithms in real time.
Understanding focus helps amateur stargazers capture clearer photos and see finer details on Jupiter or Saturn.