1. What is the maximum lens aperture?
How wide the diaphragm opens.
2. If a 50mm lens has an aperture diameter of 25mm what f stop is it set at?
Focal length/ aperture diameter = 2
3. What is a lens aberration? And why do they exist?
Problems with the lens. No lens is perfect and have some compromises.
4. What is spherical aberration? How can it be reduced?
Where light passing through the centre of the lens has a different focal point to that traversing the edge. It can be reduced by stopping down the lens.
5. What are chromatic aberrations?
Light of different colours is not focused at the same point. Causes colour fringes.
6. What do these lenses do?
a) achromatic – lens corrected for two different wavelengths
b) apochromatic – lens corrected for three different wavelengths
c) superachromatic – lens corrected for four different wavelengths
7. What is coma?
Cannot produce a sharp point away from the lens axis – looks like a comet
8. What is astigmatism?
An inability to focus sharply horizontal and vertical lines near the edge of the sensor/film
9. What is distortion? And geometric distortion?
A lens being in front of or behind the aperture causes barrel or pincushion distortion. Geometric distortion covers both of these.
10. What is curvature of field?
A lens that cannot produce a flat image of a flat subject.
11. What is a sweet spot on your lens?
Where the lens performs at its best for sharpness.
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