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  1. A proof can be found in A. C. Hardy and F. H. Perrin, The Principles of Optics (McGraw–Hill Book Co., New York, 1932) (in their discussion of telecentric optical systems), pp. 74–75.
  2. Because the eye is in the focal plane of the lens, extreme rays A′ and A″ in Fig. 1 are parallel and so are B′ and B″. Therefore, exactly the same cone of light enters the pupil A–B from each point, P, of the object, independent of d. This, together with invariant magnification, means that the image irradiance must also be invariant.
  3. A derivation is presented by G. Westheimer, Vision Res. 6, 669 (1966).
    [Crossref] [PubMed]
  4. When the system is being aligned, care must be taken to ensure that the artifical pupil and the observer’s pupil lie precisely on the optical axis of the instrument. Otherwise, axial displacement of the target will produce some lateral movement of the retinal image. Furthermore, if the eye is not precisely in the focal plane of lens L2, axial displacement of the target will cause some change of size of the retinal image.

1966 (1)

A derivation is presented by G. Westheimer, Vision Res. 6, 669 (1966).
[Crossref] [PubMed]

Hardy, A. C.

A proof can be found in A. C. Hardy and F. H. Perrin, The Principles of Optics (McGraw–Hill Book Co., New York, 1932) (in their discussion of telecentric optical systems), pp. 74–75.

Perrin, F. H.

A proof can be found in A. C. Hardy and F. H. Perrin, The Principles of Optics (McGraw–Hill Book Co., New York, 1932) (in their discussion of telecentric optical systems), pp. 74–75.

Westheimer, G.

A derivation is presented by G. Westheimer, Vision Res. 6, 669 (1966).
[Crossref] [PubMed]

Vision Res. (1)

A derivation is presented by G. Westheimer, Vision Res. 6, 669 (1966).
[Crossref] [PubMed]

Other (3)

When the system is being aligned, care must be taken to ensure that the artifical pupil and the observer’s pupil lie precisely on the optical axis of the instrument. Otherwise, axial displacement of the target will produce some lateral movement of the retinal image. Furthermore, if the eye is not precisely in the focal plane of lens L2, axial displacement of the target will cause some change of size of the retinal image.

A proof can be found in A. C. Hardy and F. H. Perrin, The Principles of Optics (McGraw–Hill Book Co., New York, 1932) (in their discussion of telecentric optical systems), pp. 74–75.

Because the eye is in the focal plane of the lens, extreme rays A′ and A″ in Fig. 1 are parallel and so are B′ and B″. Therefore, exactly the same cone of light enters the pupil A–B from each point, P, of the object, independent of d. This, together with invariant magnification, means that the image irradiance must also be invariant.

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Figures (2)

Fig. 1
Fig. 1

Basic scheme for changing the optical distance of a target T. With the eye in the focal plane of the lens, the light intercepted from any point P of the target is independent of distance d. The image of point P lies along the backward projection of the central ray through P (shown dashed), so that the angular size of the target is also invariant with d.

Fig. 2
Fig. 2

Diagram of the optical-focus stimulator. DS is the display screen and AP, the artificial-pupil plane. When the mirrors R2 and R3 are moved together in a direction orthogonal to the optic axis, the optical distance of the display screen changes, but without change of irradiance or angular size of the image on the retina.