WEEK 11

LENS:
Lens aperture is relative.
The bigger the aperture the longer the lens needs to be to compensate.
We can liken this to the torch analysis. If you hold it close to a wall the light will be small and intensely bright.. as you move further away from the wall the light becomes bigger and therefore less intense.

We learnt each F-Number is related to the focal length of the lens......
However the same F-number of any lens passes the same amount of light despite being a different diameter. So an F8 is always going to be an F8 no matter what the lens.

Lenses come with LENS ABERRATION.

WHAT?
Aberration of the lens is basically an optical error.
All lenses suffer aberration because there is no such thing as a perfect lens.
Not all aberrations are negative, some are welcomed such as soft focus.
Although there is no 'cure' for lens aberration, many of them can be corrected by using alternate errors in the lens, counteracting in a sense.


WHY?
Because of light refraction when the light is passed through glass.
The amount of refraction depends on the wavelength of light, IE some colours of light will bend more than others.
Hence different wavelengths don't focus at the same point.

SPHERICAL SURFACES FAIL TO BRING LIGHT TO A FOCUS. And most lenses uses spherical surfaces.

Sphyrical Aberration:
*Loss of contrast
*Can't bring marginal and axial rays to the same point
*Stopping down can reduce.

Chromatic Aberration:
*Has to do with colours
*Affects where/how/whether colour focuses
*causes magnification of certain colours


LONGITUDINAL & LATITUDINAL

Achromatic : corrected for 2 colours (B/G)
Apochromatic: corrected for 3 colours (R/G/B)
Superchromatice: corrected for 4 (Infared/R/G/B)

COMA aberration:
Off axis, spherical aberration...
*Creates cone shaped points
*Stopping down can reduce


Barrel and Pincushion distortion.
DOES NOT EFFECT IMAGE SHARPNESS

Geometric distortion.
Stretched to fit a film plane.