Field lens sentence example
- 17) are the eye lens and field lens respectively of a Merz positive eye-piece.
- He then altered the magnifying power by sliding the field lens of the eye-piece (which was fitted with a slipping tube for the purpose) along the eye-tube, till the images were brought into contact.
- The mere size of the apparent field of view depends upon obtaining the oblique pencils of light emerging from it to cross the axis at the great possible angle, and to this end the presence of a field-lens is indispensable, which is separated from the eye-lens by a considerable interval.
- 4) in which the field-lens is changed into a meniscus having radii in about the ratio of +I to - 9 gives still better results, but still not quite so good as the results obtained by using the combination of two convexo-plane lenses of the focal ratio 2 to I.
- The field-lens is thus in the principal focal plane of the eye-lens, if the separation be equal to -f f2).Advertisement
- This is such a practical drawback that the separation is generally 4ths or $ths of the theoretical, and then the primary image viewed by the eye piece may be rather outside the field-lens, which is a great practical advantage, especially when a reticule has to be mounted in the primary focal plane, although the edge of the field is not quite achromatic under these conditions.
- It consists of a piano-convex field-lens of crown glass.
- There are also other eye-pieces having the field-lens double or achromatic as well as the eye-lens.
- In cases where it is important to get the maximum quantity of light into the eye, the field-lens is discarded and an achromatic eye-lens alone employed.
- In order to secure the advantage of the principal focal plane of the eye-piece being well outside of the field-lens and at the same time to obtain a large flat field of view with oblique achromatism and freedom from coma and distortion, there is no better construction than the modified Kellner eye-piece (fig.Advertisement