parfocal, a.
(pɑːˈfəʊkəl)
[f. par n.1 + focal a.]
Having or pertaining to the property that corresponding focal points of different lenses lie in the same plane, so that they may be interchanged without the need to adjust the focus. Const. with.
| 1886 Microsc. Bull. & Sci. News Aug. 31/1 Referring to the article in the April issue..on ‘changing eye-pieces without altering focus, etc.’, we announce that we are prepared to furnish eye-pieces, as there described... We have named these eye-pieces parfocal, meaning ‘of equal focus’. 1944 C. P. Shillaber Photomicrography iii. 234 The objectives are said to be parfocal with each other when one setting of the microscope will serve to focus all four objectives. 1955 Sci. Amer. Feb. 122/2 This is called ‘parfocal’ mounting, and it saves a lot of time when, for example, you are searching your collection for a specific type of crystal, surface texture or color to match an unknown mineral. 1965 J. R. Benford in R. Kingslake Appl. Optics & Optical Engin. III. iv. 167 The 3·5 × objective is a comparatively recent ‘telephoto’ construction, designed to be parfocal with the high-power objectives. 1970 R. P. Loveland Photomicrography I. iii. 114 The rotating objective holder is the most convenient in use when the objectives are parfocal. 1976 Physics Bull. Nov. 511/1 To meet the recently increased demand for low magnification objectives, a parfocal distance of 45 mm has been employed. 1979 Nature 1 Mar. p. xxiii, All optical components are parfocal and permanently centred. |
Hence parfoˈcality, the property of being parfocal; parˈfocally adv.
| 1965 J. R. Benford in R. Kingslake Appl. Optics & Optical Engin. III. iv. 165 Tightening one of these and loosening the other provide a precise means of moving the objective lens up and down to bring about the desired parfocality setting, so that objectives on a multiple nose-piece can be interchanged without losing focus. 1971 J. H. Richardson Optical Microscopy for Materials Sci. i. 41 Parfocality is not an inherent property of an objective, but is rather a convenience often provided on the more modern microscopes. 1974 Physics Bull. May 197/2 For optical measurements the instrument has a high pressure xenon arc lamp and six pairs of matched condenser and objective lenses mounted parfocally in turrets. |