# The fix: the achromatic doublet

Site: Chromatic Aberration
URL:  https://3dcms.info/buckrackley/sites/chromatic-aberration/3d/the-fix
Section: Page cluster

## Page content

Cement a converging crown-glass element to a diverging flint one and the second undoes the first's color spread while keeping the focusing power. Red and blue return to a common focus. Left is one lens, two foci. Right is the doublet, one.

- Back to start <https://3dcms.info/buckrackley/sites/chromatic-aberration/3d/start>
- Dispersion <https://3dcms.info/buckrackley/sites/chromatic-aberration/3d/dispersion>
- Lateral fringing <https://3dcms.info/buckrackley/sites/chromatic-aberration/3d/lateral>
- Longitudinal fringing <https://3dcms.info/buckrackley/sites/chromatic-aberration/3d/longitudinal>
### One lens: two focal points

blue focuses short, red focuses long

### Doublet: one focal point

crown plus flint: both land together

Left: one lens, and blue lands short of red. Right: crown plus flint, and both colors land together.


## All pages
- Chromatic Aberration: Page <https://3dcms.info/buckrackley/sites/chromatic-aberration/3d/start>
- Why it happens: dispersion: Page <https://3dcms.info/buckrackley/sites/chromatic-aberration/3d/dispersion>
- Lateral aberration: Page <https://3dcms.info/buckrackley/sites/chromatic-aberration/3d/lateral>
- Longitudinal aberration: Page <https://3dcms.info/buckrackley/sites/chromatic-aberration/3d/longitudinal>
- The fix: the achromatic doublet: Page <https://3dcms.info/buckrackley/sites/chromatic-aberration/3d/the-fix>

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