| 11. | The second form of astigmatism occurs when the optical system is not symmetric about the optical axis.
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| 12. | The aperture angle is gaged symmetrically to the optical axis and has to be smaller than 180?
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| 13. | The centre of the diaphragm's aperture coincides with the optical axis of the lens system.
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| 14. | Note that the aperture must be centered on the optical axis for this to work as indicated.
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| 15. | Such a ray will be reflected from the mirror as a ray parallel to the optical axis.
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| 16. | The laser beam can be at any angle with respect to the optical axis used to collect Raman scattering.
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| 17. | :: My guess is that the light is only truly white on the optical axis of the lamp.
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| 18. | However, if the pupil is significantly off-center from the optical axis, negative chromostereopsis will ensue.
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| 19. | A pinhole cap can be used to align the optical axis of the condenser with that of the microscope.
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| 20. | By convention, the optical axis of the system is taken as the " z "-axis.
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