Celestron Advanced Stereo Microscope Microscope Basics - Page 18

Depth of Field - how much depth of field is a function of the objective lenses and means the farthest and nearest points in the field of view are in simultaneous sharp focus. Low magnification objectives have more depth of field than high magnification objectives. Depth of Focus - means the farthest and nearest points in the film plane (photomicrography) or the CCD plane (video microphotography) which are simultaneously in focus. It is just the reverse of the depth of field, where here greater depth of focus occurs with high magnification objectives. Flatness of Field - a quality describing the appearance of the field of view as being flat from edge-to-edge. Brightness - how light or dark is the image? Brightness is related to the illumination system. It is also related to the N.A. of the objective lens where the larger the N.A., the brighter the image at that power. Contrast - is the ratio of light and dark parts of a specimen or object and how well they are defined and the main part of the microscope that affects this is the illumination system. Collimation (Alignment) - this is a condition in which all optical elements are centered on the same axis. Microscope Accessories Prepared Slides - for those who do not wish to make their own slides or to supplement their collections, prepared slides are readily available. These slides can open up the world of microorganisms that lead to learning, discovery, and enjoyment. For best results use only glass slides that are 1" x 3" in size. Filters - they can be useful in providing enhanced contrast and color correction for observing but not for photography. In some cases, colored filters can be a simple substitute for staining, which would kill live specimens. They usually lay over the top of illumination systems or on more expensive microscopes they sometimes have a special holder under the condenser. Blue is the most used filter since it absorbs some of the yellow to red light from of the illumination bulbs, used in many microscopes, resulting in a more natural coloration of the specimen. Green, yellow, and frosted filters all give varying effects and all filters should be experimented with to see the actual changes they make in observations of specimens. Blank Slides - these are offered for those who want to make their own slides to observe. The higher quality ones are made of glass. Some may have a small depression or well to hold a few drops of liquid. Cover Glass (Cover Slip) - these are extremely thin, flat glass or plastic covers that go over a specimen on a glass slide that has been made by you to protect the specimen during observation and storage. They come in different thicknesses which are usually matched to a number engraved on an objective lens for best performance. Slide Making Kits - kits can contain blank slides, cover glasses, various types of stains to color objects or specimens, dissecting tools, labels, etc. which are all useful when making specimen slides. Imagers and Photo Adapters - you can do photomicrography (documenting images) through your microscope. The most common form to image (and view) through a microscope is to use digital or CCD cameras. Most imagers are used as an accessory on the microscope and use specific adapters to attach them to the eyepiece tubes of both compound and stereo microscopes - see page 8. Various adapters are available to attach digital or film cameras to certain microscopes. Specialized Accessories - some microscopes are set up to use specialized kits or adapters such as a phase contrast kit, a dark field adapter, or a polarizing kit. Optical Aberrations Aberrations are any errors that result in the imperfection of an image. Such errors can result from design, fabrication, or both. It is impossible to design an absolutely perfect microscope. Some aberrations of a minimal amount are present in all microscopes and generally are less apparent as the price of the microscope increases. So, don't be too concerned unless the aberrations are severe or bothersome. 18