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A pinhole occluder is an opaque disk with one or more small holes through it, used by ophthalmologists, orthoptists and optometrists to test visual acuity. The occluder is a simple way to focus light, as in a pinhole camera, temporarily removing the effects of refractive errors such as myopia. Because light passes only through the center of the ...
Sometimes they serve as mounts for a concrete block, which provides further isolation. Pads or sheets of flexible materials such as elastomers, rubber, cork, dense foam and laminate materials. Elastomer pads, dense closed cell foams and laminate materials are often used under heavy machinery, under common household items, in vehicles and even ...
Polished concrete may be considered a form of sustainable design flooring, if less material is used than in comparable types of flooring. [citation needed] Polished concrete floors have the following advantages: low-maintenance [7] – polished concrete is easily maintained with the use of clean water or a neutral pH cleaner. The application of ...
Interest in concrete railway sleepers increased after World War II following advances in the design, quality and production of pre-stressed concrete. Chaired bullhead concrete sleepers have been around since at least the 1940s; the Great Western using a two-holed chair, thus saving both scarce wartime timber and steel fixing bolts. [ 4 ]
The chronological steps that need to be taken for a tilt-up project are: site evaluation, engineering, footings and floor slabs, forming tilt-up panels, steel placement, embeds and inserts, concrete placement, panel erection and panel finishing. [1] [6] Once the pad (casting surface or floor slab) has cured, forms are built on top. Dimensional ...
Wide-field micrograph of a damaged 80 μm pinhole Natural pinholes formed by tree leaves – Solar eclipse of August 21, 2017 in Washington state. A pinhole is a small circular hole, as could be made with the point of a pin. In optics, pinholes with diameter between a few micrometers and a hundred micrometers are used as apertures in optical ...
A pinhole camera is a simple camera without a lens but with a tiny aperture (the so-called pinhole)—effectively a light-proof box with a small hole in one side. Light from a scene passes through the aperture and projects an inverted image on the opposite side of the box, which is known as the camera obscura effect.
Pinhole glasses, also known as stenopeic glasses, are eyeglasses with a series of pinhole-sized perforations filling an opaque sheet of plastic in place of each lens. Similar to the workings of a pinhole camera , each perforation allows only a very narrow beam of light to enter the eye which reduces the size of the circle of confusion on the ...