The optical microscope, often referred to as the "light microscope", is a type of microscope, which uses visible light and a system of lenses to magnify images of small samples. Optical microscopes are the oldest and simplest of the microscopes. Digital microscopes are now available which use a digital camera to examine a sample, and the image is shown directly on a computer screen without the need for optics such as eyepieces. All optical microscopes share the same basic components:
• The eyepiece - A cylinder containing two or more lenses to bring the image to focus for
the eye. The eyepiece is inserted into the top end of the body tube. Eyepieces are interchangeable and many different eyepieces can be inserted with different degrees of magnification. Typical magnification values for eyepieces include 5x, 10x and 20x.
• The objective lens - a cylinder containing one or more lenses typically made of glass, to
collect light from the sample. At the lower end of the microscope tube, one or more objective lenses are screwed into a circular nose piece, which may be rotated to select the required objective lens. Typical magnification values of objective lenses are 4x, 5x, 10x, 20x, 40x, 50x and 100x. Some high performance objective lenses may require matched eyepieces to deliver the best optical performance.
• The stage - a platform below the objective which supports the specimen being viewed
The stage usually has arms to hold slides (rectangular glass plates with typical dimensions of 25 mm by 75 mm, on which the specimen is mounted).
• The illumination source - below the stage, light is provided and controlled in a variety of
ways. At its simplest, daylight is directed via a mirror. Most microscopes, however, have their own controllable light source that is focused through an optical device called a condenser, with diaphragms and filters available to manage the quality and intensity of the light.
The whole of the optical assembly is attached to a rigid arm, which in turn is attached to a robust U shaped foot to provide the necessary rigidity. The arm is usually able to pivot on its joint with the foot to allow the viewing angle to be adjusted. Mounted on the arm are controls for focusing, typically a large knurled wheel to adjust coarse focus, together with a smaller knurled wheel to control fine focus.
Stereo microscope:
The stereo or dissecting microscope is designed differently from the diagrams above, and serves a different purpose. It uses two separate optical paths with two objectives and two eyepieces to provide slightly different viewing angles to the left and right eyes. In this way, it produces a three-dimensional visualization of the sample being examined.
Digital microscope:
Low power microscopy is also possible with digital microscopes, with a camera attached directly to the USB port of a computer, so that the images are shown directly on the monitor. Often called "USB" microscopes, they offer high magnifications (up to about 200×) without the need to use eyepieces, and at very low cost. The precise magnification is determined by the working distance between the camera and the object, and good supports are needed to control the image. The images can be recorded and stored in the normal way on the computer. The camera is usually fitted with a light source, although extra sources (such as a fiber-optic light) can be used to highlight features of interest in the object.
Digital microscope Modern stereo microscope optical design
2. UV-box:
UV-box is a tool used by well site geologists to examine different cutting samples under ultraviolet light for the existence of oil in these samples. Fluorescence is the emission of electromagnetic radiation light by a substance that has absorbed radiation of a different wavelength. In most cases, absorption of light of a certain wavelength induces the emission of light with a larger wavelength (and lower energy). The most striking examples of this phenomenon occur when the absorbed photon is in the ultraviolet region of the spectrum, and is thus invisible, and the emitted light is in the visible region.Practical applications of this effect are found in the UV-box.
A simple chemical test may be carried out to determine whether fluorescence in drill cuttings is a result of oil or some fluorescing mineral. This is easily and quickly established by immersing some of the drill cuttings in a petroleum solvent (chlorothene, trichlorothene, ether, or acetone). If the fluorescence is derived from mineral sources, the minerals will not dissolve in the solvent and the solvent will remain colorless under ultraviolet light. However, if hydrocarbons are present in the rock, they will disseminate into the solvent, giving the entire solvent a distinctive color under ultraviolet light. This sheen under UV light is called cut and the color of the cut indicates the quality of the oil. Pale blue-white is high gravity (light) oil, yellow is medium gravity, and orange brown
for low gravity (heavy) oil. CN-6 UV cabinet The CN-6 UV cabinet welcome one or two hand held UV
lamps (VL-6 model) in any of the three following wave lengths: 254, 365 or 312 nm.
3. Shale density balance:
KERN sensitive balance is used to precisely determine the weight of small samples not more than “200 gm”. It is used in Petroservices mud logging unit in weighing crushed cutting samples that are going to be tested for calcimetry and in shale density measurements.
These electronic scales are a precision instrument. Electromagnetic fields can cause major display discrepancies. The scales must then be repositioned away from electromagnetic fields. All sources of environmental interference, such as drafts and vibrations, should be avoided. Sudden changes of temperature should be avoided. The scales must be reset to match changes in temperature.
The scales are not hermetically sealed; therefore avoid high humidity, steam and dust. Do not bring liquids into direct contact with the scales, as these can penetrate into the measuring mechanism. Cleaning material should only be dry or barely damp. Do not use solvents as these can damage paintwork or other plastic parts. Remove damaged items immediately from the scales.
The measuring mechanism will be stabilized by allowing the scales to warm up for a few minutes after switching them on. Place items to be weighed carefully on the scales. Do not place objects on the weighing platform for any period, apart from normal use. Sudden shocks or overloading the scales beyond the maximum permitted weight should absolutely be avoided, balance could be damaged.
4. Calcigraph:
Calcigraph is used to determine the amount of calcium carbonate and magnesium carbonate in a sample of alkaline earth carbonates such as oil well cores or drilled cuttings. Calcite builds up in drilling fluids and in water, treatment processes causes scaling problems. Data from the Calcigraph can help determine the proper chemical treatment.
In calcigraph, calcium carbonate and magnesium carbonate are reacted with 10 percent hydrochloric acid in a sealed reaction cell to form CO2. As the CO2 is released, the pressure
build up is measured using either a pressure gauge or a pressure recorder. During the calibration process, a calibration curve is created by reacting HCl with pure, reagent grade CaCO3. By using a known weight of CaCO3 reagent, you can
determine the relationship between the amount of pressure released and the weight of CaCO3 in the sample. Since all
reaction cells are slightly different, this relationship will be different for each cell. Therefore, a calibration curve is required to obtain accurate results.