Entrance pupil

Figure 9. The entrance and exit pupils are the surfaces where the entrance and exit rays coming from the different field positions cross each other. In different terms, the entrance pupil is the aperture of the optical system as seen by an observer located at the position of the object, or at the location of the image for the exit one.

Deformable mirrors are usually placed at a greatly reduced image of the telescope entrance pupil - the typical diameter of PZT or PMN based deformable mirrors is in the range 10-20 cm. A completely different approach is to make one of the telescope mirrors deformable, and the best choice is the secondary mirror (relatively small and usually coincides with the aperture stop for in-... 

The diameter of a telescope entrance pupil or the distance between two telescopes determine the baseline, which determines the resolution of the interferometer in combination with the detected wavelength. The table compares the resolution of single telescopes and interferometers at optical and radio wavelengths. Note that the resolution of optical interferometers is comparable to that of radio very long baseline interferometry (VLBI). 

The entrance pupil is nothing more than the area of a lens that accepts radiation and defines the relative useful portion of the lens. Since a coherent source is a point source (zero diameter), the image in the entrance pupil will also have zero diameter and thus incoherent source is rigorously a source of infinite extent (a = >) and is only of academic interest since all light collected from any real source is always imaged within the entrance pupil, so that c is always <1. In practice, partially coherent sources are used. 

In this equation, n is the refractive index of the imaging medium and 6 is the angular aperture, the apparent angle of the lens apeiTure as seen from the focal point. The human eye has an entrance pupil of 7 mm and an NA value of 0.002. Thus, by Eq. 2.1, the human eye can resolve two objects, at a normal viewing distance and when the objects are... 

The illumination system comprises a series of relay optics and uniformizing optics that project the radiation from the source through the photomask to the entrance pupil of the projection optics of the lithographic lens, where it forms an image of the illumination source (see Fig. 13.8). This type of illumination system is referred to as Kohler illumination. The fraction of the pupil filled by the illuminator source s image determines the degree of coherence in the projection... 

The entrance pupil refers to the size and location of the entrance aperture between the light source and the remainder of an optical system. The exit pupil refers to the size and location of the exit aperture within an optical system (or train) just prior to the detector. 

Depth of focus increases with smaller apertures. For distant subjects (beyond macro range), depth of focus is relatively insensitive to focal lengfh and subject distance for a fixed / number (defined as fhe ratio of the focal length of the lens to the diameter of its entrance pupil). In the macro region, depth of focus increases with longer focal lengfh or closer subject distance, while depth of field decreases. 

The values of Op, Oq, and Op can be determined by numerical methods for a given set of system parameters from Eq. (12). However, it should be noted that there is an upper physical limit on these angles caused by a finite size of the entrance pupil of the lens. This maximum entrance pupil can be found from the NA of the lens and the focal length, /. It can be shown that this limiting angle, 0 can be calculated by solving... 

It should be noted that this observation is only true if the aperture of the system (solid angle Q) is always completely fiUed by the impinging light. This may not be the case for perfectly coUimated light sources (like lasers). However, for typical camera systems used in road vehicles, the size of the entrance pupil (i.e. the effective aperture area determining the solid angle Q) is rather small, so that the possibility of an only partially filled pupil can be neglected for aU practical purposes. 

As internal system structures or signal interfaces usually won t be disclosed by the OEM, the CMS has to be regarded as an integral system ( black box ). Therefore, the available input quantity used in a test stand is limited to the luminous flux entering the entrance pupil of the camera objective. The output quantity is compulsorily given by the luminance of the display that is used to present the scene to the observer. 

For the first case, the pragmatic choice is to actually use a typical car headlight. For the second case, an appropriate laser source can be used. It should be noted that in both cases it is very important to ensure that the entrance pupil of the CMS camera is completely filled. However, as these pupils tend to be very small, this can always (easily) be achieved by choosing a sufficientiy large distance between glare source and camera. 

The setup has to contain some additional diagnostic element to check whether the alignment was successful (i.e. to ensure that the active glare source observed by the system does actually have the defined luminance value in the direction towards the camera). As the glare source will have a known spatial extent, only the luminous intensity has to be checked for the given direction. This can be achieved by a photodiode that can be swiveled in front of the camera aperture. Ideally, this diode should have the same area as the aperture (resp. entrance pupil) of the CMS camera. 

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