Nt1310 Unit 2 Midterm

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Q2. The reason for the difference in blurring between both the horizontal and vertical lines was due to astigmatism being present. Astigmatism is an off axis aberration which caused the vertical line to appear clearer when observing the USAF target. This occurs when the beam of light converges more rapidly along the tangential direction compared to that of the sagittal direction, thus changing the beam profile from a circular one to a more elliptical one. Because the tangential focus is reached before the sagittal focus, the elliptical beam is compressed into a straight perpendicular line. This made the vertical lines appear clearer and sharper. Therefore the horizontal and vertical lines did not blur equally

Q3. The optical quality of an …show more content…

The wavelength of light emitted by sodium light sources is made up of yellow wavelengths from 589.0 - 589.6nm so no colour version is possible. These lights may not be ideal at night time this is because, the human eye cannot function fully in the photopic state, and its colour sensitivity shifts to the scotopic night vision conditions. This phenomenon is known as the Purkinje shift. Herein lies a deficiency of our measure of light because it is based on the normal daylight sensitivity curve of the eye. At very low light levels, one really should to instead rate lamps in terms of their scotopic luminous flux, Due to the Purkinje shift, low pressure sodium lighting becomes less and less efficient at low illuminance …show more content…

The distance between the target and first focal point (fs) of the standard lens were measured to give χ. The focimeter equation〖[F〗_t=F_(s^2 ) x] was used to work out the correct power of the lenses (Ft). A graph was plotted with Ft being the Y value (in dioptres) and χ being the X variable (in metres). Fs2 remained constant. A line of best fit was drawn from the results which gave the power of the unknown lenses. The equation of the line of best fit was[Y = 100x]

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