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Describes a microscope with interchangeable objectives that do not require refocus.
[L. par, equal, + focal]
Medical Dictionary for the Health Professions and Nursing © Farlex 2012
References in periodicals archive ?
Although Sigma does make a really nice and fast 18-35mm f/1.8 zoom lens, it isn't parfocal, so you can't actually zoom optically while filming and still hold manual focus.
Parfocal: A method of setting up the microscope in order to have similar focal distances for objectives of different magnifications.
Digital Smartcam Technology offers instant camera recognition for consistent, easy image optimization, and an integrated 2x parfocal optical zoom (14- to 28-mm) provides optimal image size with all telescopes, reducing camera/telescope movement.
The system is fully motorised with microprocessor control, and the lens offers parfocal selection of five effective focal lengths, four selectable filters and a four-line backlit display of focal length, filter position, focus range and operating status.
Both magnifications are parfocal (in focus) and telecentric (object size does not change as focus moves through depth of field), features essential for maintaining dimensional accuracy.
The DeLite eyepieces are parfocal with others in the series, as well as Tele Vue's 1 1/4-inch Plossl, Panoptic, Nagler, and Delos eyepieces, and accept its Dioptrx correctors.
At $2,500, this designed-for-4K camera--with its 4.8x full frame parfocal zoom lens with constant f/4 aperture; discrete zoom, focus, and iris rings; optical stabilization; and power zoom--means native E-mount lenses are now a strength and no longer a weakness for Sony E-mount video cameras.
The microscope line also includes 3-D binocular and Stereo-Zoom trinocular systems, and Video-Zoom, with a wide range of standard features and accessories such as extra-large (22 mm) eyepieces, coated prism optics, parfocal zoom, 90 mm working distance, metal body for ESD safety, 45[degrees] eyepieces, and protective eyeguards.
To maximize performance, Nikon designers set the focal length of the tube lens for the infinity system at 200 mm and chose 60 mm as the parfocal length of the objective.
Using the optical formula of the still lens, Tokina engineers have created a lens that is parfocal, has reduced breathing and image shift, and a de-clicked, 9-bladed, curved iris for precise exposure control.
Each Mega Wide Angle eyepiece incorporates blackened lens edges to enhance contrast, and their parfocal design requires little or no focus change when switching between eyepieces within the series.
DSLR lenses are also not typically parfocal, which means they cannot hold their focus when zooming in and out.