Maximum Lens Aperture
- how big the hole/aperture can go
- biggest hole in the diaphram
what does 1:1.4 indicate?
ration= max aperture diameter: lens focal length
eg: if lens focal length= 50mm
maximum diameter=35.7mm
Relative lens aperture
focal length 35mm
max aperture f2
max aperture diameter 175mm
focal length 105mm
m.a f2
m.a.d 52.5mm
f2 on 25mm ad of 12.5
f2 on 50mm ad of 25mm
f2 on 100mm a.d of 50mm
Aberation 'n' stuff
an optional error
no lens is perfect
can be corrected by introducing alternative errors in lens
some errors are welcomed- soft focus lens
Why do aberrations exist?
- light is bent ir refracted as it passes through glass
- spherical surfaces fail to bring light to a focus.
-most lens elements have spherica surface
-lenses cannot bring marginal and axial rays to same point light from edge focuses -nearer lens
-loss of contrast
-stopping down can reduce this abbertaion
-can be reduced by delibertaion use of other aberrations
-can be reduced by deliberate use of other aberrations
Achromatic, corrected for 2, blue and green
Apochromatic, corrected for 3, blue, green and red.
--
colours focusing at different distances leads to blurring with symmetrical colour fringing
coma (not cooma)
