Aluminum grating

There is a wealth of information inscribed on the barrel of each objective, which can be broken down into several categories. These include the linear magnification, numerical aperture value, optical corrections, microscope body tube length, the type of medium the objective is designed for, and other critical factors in deciding if the objective will perform as needed. A more detailed discussion of these properties is provided below and in links to other pages dealing with specific issues.

Welded Heavy-Duty products are designed to meet the need for gratings subject to heavy rolling and static loads such as highways, plant floors, loading docks, inlet covers and airports. Since these conditions can range from light-duty forklifts to semi-trucks and trailers carrying maximum allowable highway loads, heavy duty gratings are manufactured in a wide variety of bar sizes and spacings. Indiana Gratings Heavy-Duty products are designed in accordance with current AASHTO specifications for H-10 through H-20 loads. Automobile and forklift loads are similarly evaluated with loads calculated and distributed in accordance with the criteria shown below. If your particular load conditions are not adequately addressed in the load criteria presented, please contact our engineering staff and we will be pleased to assist in the selection of a heavy-duty grating to satisfy your specific needs.

The objective depicted on the left in Figure 3 has a parfocal distance of 45mm and is labeled with an immersion medium color code in addition to the magnification color code. Parfocal distance is measured from the nosepiece objective mounting hole to the point of focus on the specimen as illustrated in the figure. The objective on the right in Figure 3 has a longer parfocal distance of 60 millimeters, which is the result of its being produced to the Nikon CFI60 200/60/25 Specification, again deviating from the practice of other manufacturers such as Olympus and Zeiss, who still produce objectives with a 45mm parfocal distance. Most manufacturers also make their objective nosepieces parcentric, meaning that when a specimen is centered in the field of view for one objective, it remains centered when the nosepiece is rotated to bring another objective into use.

The cross bars listed for Severe Loading are optional and will provide superior rigidity and durability when gratings are subjected to intense, continuous or repetitious traffic. Ideal for trench covers, highways and inlet grates, these cross bars enhance lateral stiffness thereby extending the service life of the grating. When specifying gratings with bearing bars centered at 1-3/8”, 1-7/8” or 2-3/8”, consideration of Severe Loading cross bars is highly recommended. NOTE: IN THE EVENT THAT A CROSS BAR SIZE IS NOT SPECIFIED, THE CROSS BAR SHALL BE SELECTED AT THE DISCRETION OF THE MANUFACTURER.

Embed Frames cast into concrete floors and substructures serve a multitude of purposes that extend the effective life of your completed construction project. Frames form a permanent shield for concrete lead edges and perimeters which are subject to cracking and chipping when left unprotected. During construction, these rigid 1/4" (minimum) thick steel frames expedite forming and provide a welded structure that assures accuracy in the concrete pour. Frames provide a uniform bearing surface for grates or covers, often eliminating rocking or irregular elevations experienced with covers installed on poured concrete. In specifying Indiana Gratings Embed Frames, you are specifying durability, accuracy and economy. (Nail holes are optional and may further expedite installation. If desired, size and location should be specified.)

Bar Grating

While bearing bar selection is critical for specifying a proper heavy-duty grating for your application, the life-cycle of your installation will often be influenced by selection of the appropriate cross bar. The table below details alternative cross bar sizes available. The sizes listed for Standard Loads are the standard twisted square or round cross bars supplied by Indiana Gratings for a particular bearing bar size. These sizes have been selected to maximize manufacturing efficiency and economy. It is suggested that these sizes be specified when the grating is subject to intermittent traffic and only occasional full capacity loading.

The safe spans indicated for heavy duty gratings and bridge decking in the preceding load tables are based upon simple span calculations. When the grating is properly anchored and the span is continuous over 3 or more supports, the above spans may be increased by a multiple of 1.20.

Special Features - Objectives often have additional special features that are specific to a particular manufacturer and type of objective. The plan apochromat objective illustrated in Figure 1 has a spring-loaded front lens to prevent damage when the objective is accidentally driven onto the surface of a microscope slide.

Trench Grating Systems by Indiana Gratings allow the specifier to combine any of the gratings illustrated above with any of the embed frames profiled on page 14. Gratings are available in Standard series for pedestrian loads or Heavy Duty series for vehicular traffic. Unlike cast iron or molded trench products, this flexible system allows the user to specify the exact clear opening ("S" dimension) desired. Because Indiana Gratings offers five distinct embed frame profiles, the user can select a frame to meet the exact edge condition desired. Bolting the grates to the frames is optional and must be specified. All gratings are provided with plain surface (the optional serrated surface is also available when specified) and open ends are trench banded to maximize drain capacity. Unless otherwise noted, all trench frames and grating are hot dip galvanized after fabrication in accordance with ASTM Specification A-123.

Multilayer Coatings - Quality microscope objectives are protected and enhanced by unique high-transmission anti-reflective multilayer coatings that are applied to the lens air-interface surfaces to reduce flare and ghosts and ensure high-contrast images. These specialized coatings are also used on the phase plates in phase contrast objectives to maximize contrast.

Steelgratings

Once the bar spacing is selected, the bearing bar size must be specified based upon the anticipated load and the clear (unsupported) span to be served. The load tables on pages 11-13 provide the maximum safe clear simple span for our most popular products based on the maximum traffic conditions defined. These tables incorporate strict limitations where design deflection shall not exceed the lesser of L/400 of the safe span indicated or 1/8 of one inch (.125).

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Microscope manufacturers offer a wide range of objective designs to meet the performance needs of specialized imaging methods, to compensate for cover glass thickness variations, and to increase the effective working distance of the objective. Often, the function of a particular objective is not obvious simply by looking at the construction of the objective. Finite microscope objectives are designed to project a diffraction-limited image at a fixed plane (the intermediate image plane), which is dictated by the microscope tube length and located at a pre-specified distance from the rear focal plane of the objective. Microscope objectives are usually designed to be used with a specific group of oculars and/or tube lenses strategically placed to assist in the removal of residual optical errors. As an example, older Nikon and Olympus compensating eyepieces were used with high numerical aperture fluorite and apochromatic objectives to eliminate lateral chromatic aberration and improve flatness of field. Newer microscopes (from Nikon and Olympus) have objectives that are fully corrected and do not require additional corrections from the eyepieces or tube lenses.

Diffractiongratings

All grating must be firmly fastened in place. Welding panels to the supporting structure provides a superior, permanent installation. Gratings subject to removal can be fastened with Weld Lugs which are shop welded between the bearing bars, or anchored with Saddle Clips. These fasteners, which are provided upon request, are punched with 5/16" holes to receive 1/4" bolts or screws (bolts or screws supplied by others). In areas where welding or drilling is not permitted, "G" Clips can provide the fastening solution. These clips install on the top surface of the grating and create a friction connection with the flange supporting the panel. The narrow spacing of close mesh gratings allows for countersinking of the bearing bars and fastening with flat head screws.

InterstateGratings

Bridge Decking is manufactured by cold-press riveting truss shaped recticuline bars to rectangular bearing bars. The resulting product is an exceptionally durable heavy duty grating with superior stiffness and lateral stability. Bridge decking is often the preferred heavy duty grating for concentrated or stress applications subject to impact and repetitive loads. Common applications include bridge floors, highways, inlets, and airport trench drain covers.

Grating panels are manufactured in nominal 24" and 36" standard widths. When considering alternative widths, consult the table below to select widths that will maintain consistent out to out spacing of the bearing bars. Widths specified which deviate from the table below can be fabricated utilizing side banding. In so doing, the outside bearing bar spacing on one side of the finished panel will deviate from the spacing throughout the rest of the panel.

Identification of the properties of individual objectives is usually very easy because important parameters are often inscribed on the outer housing (or barrel) of the objective itself as illustrated in Figure 1. This figure depicts a typical 60x plan apochromat objective, including common engravings that contain all of the specifications necessary to determine what the objective is designed for and the conditions necessary for proper use.

Bar Grating Sizes

Types ofgratings

Parfocal Distance - This is another specification that can often vary by manufacturer. Most companies produce objectives that have a 45 millimeter parfocal distance, which is designed to minimize refocusing when magnifications are changed.

The interactive tutorial above allows the visitor to adjust the correction collar on a microscope objective. There are some applications that do not require objectives to be corrected for cover glass thickness. These include objectives designed for reflected light metallurgical specimens, tissue culture, integrated circuit inspection, and many other applications that require observation with no compensation for a cover glass.

Heavy Duty vehicular grates are illustrated on page 15 of this catalog. Inlets may be specified to any clear opening by simply indicating the desired "W" (width) and "S" (span) dimensions illustrated on page 14. Similar to our trench grating systems, any of the five embed frame profiles may be specified to meet the exactneeds of your application. Bolting the grates to the frames is optional and must be specified. While all gratings are manufactured with plain walking surface, the optional serrated surface may be specified. The ends of all inlet gratings are trench banded to enhance durability and allowfor maximum drainage. Unless otherwise specified, all inlet grates and frames are hot dip galvanized in accordance with ASTM specification A-123.

Investigate how internal lens elements in a high numerical aperture dry objective may be adjusted to correct for fluctuations in coverslip thickness.

Because heavy-duty gratings are commonly subjected to shock and impact loads it is highly recommended that all open ends be banded. The welded band bar helps distribute impact loads and minimizes panel distortion when subjected to repetitious traffic patterns.

Steel Bar Grating

Glass Design - The quality of glass formulations has been paramount in the evolution of modern microscope optics. Numerous designs have been implemented by a variety of manufacturers, but we will limit this discussion to a specialized low dispersion glass formulation. Extra Low Dispersion (ED) glass was introduced as a major advancement in lens design with optical qualities similar to the mineral fluorite but without its mechanical and optical demerits. This glass has allowed manufacturers to create higher quality objectives with lens elements that have superior corrections and performance.

Complimenting our trench grating systems, Indiana Gratings Inlet Gratings and Frames provide the specifier with flexible solutions to inlet drain requirements. Equal to our trench grating products, Standard Duty pedestrian grates and

Indiana Gratings Trench Grating Systems and Inlet Sets combine our most popular gratings and embed frames to provide economic, modular components for construction projects. These products are offered in our Standard series, designed to serve pedestrian loads, and our Heavy Duty series, designed to service the most demanding vehicular traffic. Each series is offered with multiple bar spacings (shown below) to address the specific needs of your application.

Some objectives specifically designed for transmitted light fluorescence and darkfield imaging are equipped with an internal iris diaphragm that allows for adjustment of the effective numerical aperture. Abbreviations inscribed on the barrel for these objectives include I, Iris, and W/Iris. The 60x apochromat objective illustrated above has a numerical aperture of 1.4, one of the highest attainable in modern microscopes using immersion oil as an imaging medium.

To attain higher working numerical apertures, many objectives are designed to image the specimen through another medium that reduces refractive index differences between glass and the imaging medium. High-resolution plan apochromat objectives can achieve numerical apertures up to 1.40 when the immersion medium is special oil with a refractive index of 1.51. Other common immersion media are water and glycerin. Objectives designed for special immersion media usually have a color-coded ring inscribed around the circumference of the objective barrel as listed in Table 3 and described below. Common abbreviations are: Oil, Oel (oil immersion), HI (homogeneous immersion), W, Water, Wasser (water immersion), and Gly (glycerol immersion).

Although not common today, other types of adjustable objectives have been manufactured in the past. Perhaps the most interesting example is the compound "zoom" objective that has a variable magnification, usually from about 4x to 15x. These objectives have a short barrel with poorly designed optics that have significant aberration problems and are not very practical for photomicrography or serious quantitative microscopy.

Other features found on specialized objectives are variable working distance (LWD) and numerical aperture settings that are adjustable by turning the correction collar on the body of the objective as illustrated in Figure 2. The plan fluor objective on the left has a variable immersion medium/numerical aperture setting that allows the objective to be used with multiple different immersion media, including oil, water, and glycerin. The plan apo objective on the right has an adjustable working distance control (termed a "correction collar") that allows the objective to image specimens through glass coverslips of variable thickness. This is especially important in dry objectives with high numerical aperture that are particularly susceptible to spherical and other aberrations that can impair resolution and contrast when used with a cover glass whose thickness differs from the specified design value.

Indiana Gratings Trench Systems and Inlet Sets are manufactured as component products with the grates easily removed for clearing debris from the trenches or inlets. Often security concerns or traffic conditions dictate that the grates must be bolted to the framing. When this option is specified, weld lugs or counter-sunk lands (below) are installed on the grates and the bolt is installed below the traffic surface of the grating. For high security applications, bolted grates with tamper-resistant fasteners may be further specified.

From the discussion above it is apparent that objectives are the single most important element of a microscope. It is for this reason that so much effort is invested in making sure that they are well-labeled and suited for the task at hand.

Michael W. Davidson - National High Magnetic Field Laboratory, 1800 East Paul Dirac Dr., The Florida State University, Tallahassee, Florida, 32310.

As stated above, stock grating panels are manufactured in 24" and 36" nominal widths. Stock lengths (span) are 24'-0" for all sizes with most popular bearing bar sizes also available in 20'-0" lengths. These sizes allow for efficient layout and waste minimization when they are fabricated to your exact specification.Unlike many competing products, individual grating panels do not require supports on all four sides of each cut piece. Bar grating panels only require support perpendicular to the bearing bar span. There is no need to place supports parallel to the bearing bars where adjacent panels are installed in succession.The following layouts illustrate proper layout and support of a simple bar grating platform.

World-class Nikon objectives, including renowned CFI60 infinity optics, deliver brilliant images of breathtaking sharpness and clarity, from ultra-low to the highest magnifications.

Most manufacturers have now transitioned to infinity-corrected objectives that project emerging rays in parallel bundles from every azimuth to infinity. These objectives require a tube lens in the light path to bring the image into focus at the intermediate image plane. Infinity-corrected and finite-tube length microscope objectives are not interchangeable and must be matched not only to a specific type of microscope, but often to a particular microscope from a single manufacturer. For example, Nikon infinity-corrected objectives arenot interchangeable with Olympus infinity-corrected objectives, not only because of tube length differences, but also because the mounting threads are not the same pitch or diameter. Objectives usually contain an inscription denoting the tube focal length correction as will be discussed.