Comparing the Human Eye and a Camera The human eye is a wonderful instrument, relying on refraction and lenses to form images. There are many similarities between the human eye and a camera, including: a diaphragm to control the amount of light that gets through to the lens. This is the shutter in a camera, and the pupil, at the center of the iris, in the human eye. a lens to focus the light and create an image. The image is real and inverted. a method of sensing the image. In a camera, film is used to record the image; in the eye, the image is focused on the retina, and a system of rods and cones is the front end of an image-processing system that converts the image to electrical impulses and sends the information along the optic nerve to the brain. The way the eye focuses light is interesting, because most of the refraction that takes place is not done by the lens itself, but by the aqueous humor, a liquid on top of the lens. Light is refracted when it comes into the eye by this liquid, refracted a little more by the lens, and then a bit more by the vitreous humor, the jelly-like substance that fills the space between the lens and the retina.

The lens is critical in forming a sharp image, however; this is one of the most amazing features of the human eye, that it can adjust so quickly when focusing objects at different distances. This process of adjustment is known as accommodation. Consider the lens equation: 1/f = 1/di + 1/do With a camera, the lens has a fixed focal length. If the object distance is changed, the image distance (the distance between the lens and the film) is adjusted by moving the lens. This can't be done with the human eye: the image distance, the distance between the lens and the retina, is fixed. If the object distance is changed (i.e., the eye is trying to focus objects that are at different distances), then the focal length of the eye is adjusted to create a sharp image. This is done by changing the shape of the lens; a muscle known as the ciliary muscle does this job. Correcting Nearsightedness: Correcting Farsightedness: Correcting Nearsightedness A person who is nearsighted can only create sharp images of close objects. Objects that are further away look fuzzy because the eye brings them in to focus at a point in front of the retina.

To correct for this a lens can be placed in front of the eye. What kind of lens is necessary? A converging lens A diverging lens We need a diverging lens to diverge the light rays just enough so that when the rays are converged by the eye they converge on the retina, creating a focused image. Correcting Farsightedness A farsighted person can only create clear images of objects that are far away. Close objects are brought to a focus behind the retina, which is why they look fuzzy. What kind of lens is needed to correct this? A converging lens A diverging lens Flower names in English, French and Latin. Flower name with flower meaning - the Language of Flowers A.* *As many of these English flower names are but little used, the French and Latin synonyms are given in parallel columns. English flower names French flower names Latin flower names Meaning of flowers Acacia, Acacia, Acacia, Platonic love. Acacia, rose, Acacia, rose, Acacia, rosea, Elegance. Acanthus, Acanthe, Acanthus, Arts. Almond-tree, Amandier, Amygdalus, Thoughtlessness.

Aloes, parrot-bill, Aloï¿½s, bee de perroquet Small talk. Aloes, socotrine, Aloï¿½s, socotrine, Aloe, succotrina, Bitterness and pain. Amaranth, Amaranthe, Amaranthus, Immortality. American Aloe, Agavï¿½, Agave Americana, Security. Angelica, Angelique, Angelica, Inspiration. Anthericum, Phalangï¿½re, Phalangium, Antidote. Arum, Gouet, commun, Arum vulgare, Ardor. Arum, Fly-catching, Arum, gobe-mouche, Arum crinitum, Snare. Ash, Frï¿½ne ï¿½levï¿½, Fraxinus excelsior Greatness. Ash-leaved Trumpet-flower, Jasmin de Virginie, Biguonia radicans, Separation. Aspen, Peuplier tremble, Populus tremula, Groan. Aster, china, Marguerite-reine, Aster chinensis, Variety. B.

Balm Melisse citronelle, Melissa officinalis, Joke. Balsam of Peru, Baume du Perou, Myroxylon, Cure. Barberry, Epine-vinette, Berberis, Sourness. Basil, Basilic, Ocimum, Hatred. Beech-tree, Hï¿½tre commun, Fagus sylvatica, Prosperity. Bellflower, Campanule, Campanula, Indiscretion. Bellflower, pyramidal, Pyramidale bleue, Campanula pyramidalis, Constancy. Bindweed, purple, Liseron pourpre, Convolvulus purpureus, Eminence. Bindweed, field, Liseron des champs, Convolvulus arvensis, Humility. Bird cherry-tree, Lauier-amandier, Prunus padus, Perfidy. Black thorn, Epine noire, Prunus sylvestris, Difficulty. Bladder-senna, Baguenaudier, Colutea arborescens Frivolous amusement. Bluebottle, Bluet, Centaurea cyanus, Delicacy.

Borage, Bourrache, Borage, Bluntness. Box, Buis, Buxus, Stoicism. Bramble, Ronce, Rubus, Envy. Broom-rape, Orobanche majeure, Orobauche major, Union. Broom, Spanish, Genï¿½t dï¿½Espagne, Genista juncea, Cleanliness. Broom, prickly, Genï¿½t ï¿½pineux, Genista spiniflora, Misanthropy. Bryony, Tame commun, Tamus communis, Support. Buck-bean, Menyauthe, Menyanthes, Quiet; repose. Bugloss, Buglosse, Anchusa, Falsehood. Burdock. Bardane, Aretium Lappa Importunity. C. Cactus, Cactier, Cactus, Maternal love. Catch-fly, night-flowering, Silï¿½nï¿½, fleur de nuit, Silene noeturna, Night. Celsia, great flowered, Celsie ï¿½ Crete, Celsia cretica, Immortality.

Chaste-tree, Gattilier commun, Vitex, Coldness, Cherry-tree, Cerisier, Cerasus, Education. Chestnut-tree, Chataignier, Castanea Justice. Chestnut-tree, horse, Marronnier dï¿½Inde, ï¿½sculus hippocastanum, Luxury. Christmas aconite, Hellebore de Noï¿½l, Helleborus, Wit. Cinquefoil, Quinte-feuille, Potentilla Beloved daughter. Clove-tree, Giroflier, Caryophyllus aromaticus, Dignity. Columbine, Ancolie, Aquilegia, Folly. Coltsfoot, sweet-scented, Tussilage odorant, Tussilago fragrans, Justice. Coriander, Coriandre, Coriandrum, Hidden worth. Cornel-tree, Cornouiller, Cornus, Duration. Crown-imperial, Couronne impï¿½riale, Fritillaria imperialis Power. Crowfoot, marsh, Renoncule scï¿½lï¿½ate, Rannuculus sceleratus, Ingratitude.

Crowfoot, meadow, Renoncule, bouton dï¿½or, Ranunculus aeris, Perfidy. Currant, Groseiller, Ribes rubrum, Thankfulness. Cypress Cyprï¿½s, Cupressus, Mourning. D. Daffodil , common, Narcisse des prï¿½s, Narcissus sylvestris, Deceitful hopes. Dahlia, Dahlia, Dahlia, Novelty. Dandelion, Pissenlit, Leontodon, Oracle. Daisy, double, Paquerette double, Dellis hortensis, Affection. Daisy, single, Paquerette simple Bellis simplex, Innocence. Daisy , wild, Marguerite des prï¿½s, Bellis perennis, Dost thou love me? Date-plum, Plaqueminier, Diospyros, Resistance. Day-lily, yellow, Belle de jour, Hemerocallis flava, Coquetry. Dittany of Crete, Dietame de Crete Origanum Dictamnus, Birth. Dittany, white, Fraxinelle, Dictamnus Fire.

Dock, Patience, Rumex, Patience. Dodder, Cuscute, Cuscula, Baseness. Dragon-plant, Arum serpentaire, Arum dracunculus, Dread. E. Elastic Momordica, Momordique ï¿½lastique, Momordica elaterium, Critique; hoax. Enchanterï¿½s Nightshade, Circï¿½e, Cichorium intybus, Frugality. Everlasting, Gnaphale, Gnaphalium, Perpetual remembrances. F. Fennel, Fenouil, Anethum fï¿½niculum, Strength. Fern, (sic) Fongï¿½re, (Fougere) Filix, Sincerity. Fieldrush, Jone des champs, Juncus campestris, Docility. Fig Marigold, Ficoï¿½de glaciale, Mesembryanthemum chrystallinum, Coldness of heart. Fir, Sapin, Ables, Height. Flax, Lin, Linum usitatissimum, Benefactor. Foxglove, Digitale, Digitalis, Occupation.

Funitory, Fumeterre commune, Fumaria, Gall. G. Geranium, clouded, Gï¿½ranium triste, Geranium nubilum, Melancholy. Geranium, rose, Gï¿½ernium rose, Geranium roseum, Preference. Geranium, scarlet, Gï¿½ranium ï¿½carlate, Geranium coccineum, Stupidity. Gilliflower, Mahon, Giroflï¿½e de Mahon, Cheiranthus mahoneus, Promptness. Gilliflower, stock, Giroflï¿½e des jardins, Cheiranthus lucanus, Enduring beauty. Goats-rue, Galï¿½ga, Galega, Reason. Goosefoot, Auserine ambroisï¿½e, Chenopodium, Insult. Grape-vine, Vigne, Vitis, Intoxication. Grass, Gazon, Gramen, Utility. Grass, quaking, Brise tremblante, Briza media, Frivolity. H.

Hair-moss, Polytric ï¿½ urne, Polytrichum, Secret. Hawthorn, Aubï¿½pine Cratï¿½gus oxyacantha, Hope. Hazel, Noisettier, Corylus, Reconciliation. Heath, Bruyï¿½re commune, Erica vulgaris, Solitude. Helenium, smooth Hï¿½lï¿½nie dï¿½automne, Helenium autumnale, Tears. Hepatica, Anemone hï¿½patique, Anemone hepatica, Trust. Hogbean, Jusquiame, Hyoscyamus, Defect. Hollowroot, Adoxa, Adoxa moschatellina, Weakness. Holly, Houx, Ilex, Forecast. Hollyhock, Rose trï¿½miï¿½re, Alcea rosea, Fruitfulness. Honesty, Lunaire, Lunaria, Forgetfulness. Honeysuckle, (sic) Chï¿½ve-feuille, Lanicera caprifolium, Bonds of love. Hop, Houblon, Humulus lupulus, Injustice.

Hornbeam Charme, Carpinus, Ornament. Hortensia, Hortensia, Hortensia opuloides, Carelessness. Hyacinth, expanded, Hyacinthe ï¿½talï¿½e, Hyacinthus elatus, Benevolence. Hyacinth, garden, Hyacinthe dï¿½Orient, Hyacinthus orientalis, The language of flowers. Hyacinth, wild, Hyacinthe sauvage, Hyacinthus sylvestris, Play. Hybrid crinum, Crinole hybride, Crinum, Delicate weakness. I. Immortal flowers, Immortelle, Xeranthemum annuum, Unfading remembrance. Indian cane, Balisier, Arundo bambos, Rendezvous. Ipomen, scarlet, Ipomï¿½e ï¿½carlate, Ipomï¿½a coccinea, Embrace. Iris, Iris, Iris, Message. Iris, flaming, Iris flambï¿½, Iris flammea, Flame. Ivy, Lierre, Hedera helix, Friendship. J.

Jamaica Plum, Myrobalan, Spondias myrobalanus, Privation. Japan rose, Camellia, Camellia japonica, Gratitude. Jessamine, common white, Jasmin commun, Jasminus officinale, Amiability. Jessamine, Spanish, Jasmin dï¿½Espagne, Jasminum grandiflorum, Sensuality. Jonquille, Jonquille, Narcissus jonquilla, Desire. Juniper Genï¿½vrier, Juniperus, Succor. K. Kingï¿½s-spear Asphodï¿½le jaune, Asphodelus, Regret. L. Laburnum, Cytise faux ï¿½bï¿½nier, Cytisus laburnum, Blackness. Ladiesï¿½ Bedstraw, Grateron, Galium, Rudeness. Ladiesï¿½ Ear-drop, Fuchsia, Fuchsia, Frailty. Larch, Mï¿½lï¿½ze, Pinus Larix Audacity. Larkspur, Pied dï¿½alouette, Delphinium, Levity.

Lavender, Lavande aspic, Lavandula spica, Distrust. Laurel, Laurier franc, Laurus, Glory. Laurestine, Lauier-tin, Viburnum tinue, Delicate attentions. Lichen, Hï¿½patique, Lichen hepatica, Confidence. Lilac, Lilas commun, Lilac vulgaris, Earliest love. Lilac, white, Lilas blanc, Lilac alba, Youth. Lily, Lis, Lilium, Majesty. Lily, daffodil, Amaryllis jaune, Amaryllis lutes, Pride. Lily of the Valley, Muguet de Mai, Convallaria maialis, Return of happiness. Lime-tree, Tilleul, Tilia, Conjugal affection. Lucerne, Luzerne, Medicago, Life. M. Madder, Garance, Rubia, Calumny. Madder, yellow, Alysse saxatile, Alyssum saxatile, Tranquility. Maidenhair Capillaire, Adiantum, Discretion.

Manchineel, Mancenillier, Hippomanes mancinella, Betrayal. Mandrake, Mandragore, Atropa Mandragora, Scarcity. Maple, Erable champï¿½tre, Acer, Reserve. Marigold, cape, Souci pluvial, Calendula pluvialis, Presage. Marigold, garden, Souci commun, Calendula officinalis, Trouble. Marshmallow, Guimauve, Althï¿½a, Beneficence. Marvel of Peru, Belle de nuit, Mirabilis, Timidity. Meadow-saffron, Colchique, Colchicum, Autumn. Meadow-sweet, Spirï¿½e ulmaire, Spirï¿½a ulmaria, Uselessness. Mezereon, Laurï¿½ole bois gentil, Daphne mezereum, Desire to please. Milfoil, Achillï¿½e Achillea, War. Milkwort, Polygala, Polygala, Hermitage. Mistletoe, Gui, Viscum album, Parasite.

Motherwort, Clandestine, Lathrï¿½a clandesina, Concealed love. Mugwort, Armoise, Artemisia, Happiness. Mulberry, black, Muier noir, Morus niger, Devotedness. Mulberry, white, Murier blanc, Morus albus, Prudence. Myrtle, Myrte, Myrtus Love. N. Narcissus, white, Narcisse des poï¿½tes, Narcissus poeticus, Selfishness. Nettle, Ortie, Urtica, Cruelty. Nightshade, Morelle, Solanum, Truth. Nosegay, Bouquet, Florum fasciculus, Gallantry. O. Oak, Chï¿½ne, Quercus, Hospitality. Olive, Olivier, Oliva, Peace. Ophrys, fly, Ophrise-mouche, Ophrys myoides, Mistake. Ophrys, spider, Ophrise-arraignï¿½e, Ophrys arachnites, Dexterity. Orange-blossom, Fleur dï¿½oranger, Flos aurantii, Chasity.

Orange-tree, Oranger, Aurantium, Generosity. Osmunda, Osmonde, Osmunda, Revery. P. Pansy, Pensï¿½e, Viola tricolor, Thought. Parsley, Persil, Apium, Feast. Pasque-flower, Coquelourde, Anemone pulsatilla, Without pretension. Passion-flower, Grenadille bleue, Passiflora cerulea, Belief. Peony, common, Pivoine officinale, Pï¿½onia officinalis, Shame. Peppermint, Menthe poivrï¿½e, Mentha piperita, Warmth of feeling. Periwinkle, Pervenche, Vinca, Sweet remembrance. Persian Candy-tuft, Ibï¿½ride de Perse, Iberis semperflorens, Indifference. Pheasantï¿½s-eye, Adonide, Adonis, Painful remembrance. Pimpernel, red, Mouron rouge, Anagallis phï¿½nicea, Appointment. Pine, Pin, Pinus, Boldness.

Pineapple, Ananas, Bromelia ananas, Perfection. Pink, clove, ï¿½illet des fleuristes, Dianthus caryophyllus, True love. Pink, musk, ï¿½illet mignardise, Dianthus moschatus, Childishness. Pink, yellowish, ï¿½illet jaune, Dianthus luteus, Unreasonableness. Plane-tree, Platane, Platanus, Genius. Polemonium, Polï¿½moine bleue, Polemonium ceruleum, Rupture. Pomegranate, Grenadier, Punica granatum, Foppery. Poplar, black, Peuplier noir, Populus niger, Courage. Poplar, white, Peuplier blanc, Polulus alba, Time. Poppy, corn, Pavot coquelicot, Papaver rhï¿½as, Ephemeral charms. Poppy, white, Pavot blanc, Papaver albus, Dormant affection. Prickly-pear, Raquette-figuier dï¿½Inde, Cactus opuntia, I burn.

Primrose, Primevï¿½re, Primula, Early youth. Privet, Troï¿½ne, Ligustrum, Prohibition. Prune-tree, Prunier, Prunus, Promise. Prune, wild, Prunier sauvage, Prunus sylvestris, Independence. R. Reed, Rosean, Arundo, Imprudence; music. Rest-harrow, Bugrane arrï¿½te-bï¿½uf, Ononis, Obstacle. Rose , Rose, Rosa, Beauty. Rosebay, Laurier-rose Nerium oleander, Distrust. Rosebay, Willow-herb Epilobe ï¿½ ï¿½pi, Epilobium spicatum, Production. Rosebud, Bouton de rose, Rosï¿½ calyx, Young girl. Rose capucine, Rose capucine, Splendor. Rose, hundred-leaved, Rose cent-feuille, Rosa centifolia, Graces. Rosemary, Romarin, Rosmarinus, Healing balm. Rose, moss Rose mosseuse, Rosa muscosa, Voluptuous love.

Rose, musk, Rose musquï¿½e, Rosa moschata, Capricious beauth. Rose, perpetual, Rose des quatre saisons, Rose perpetua, Unfading beauty. Rose, Provence, Rose pompon, Rosa provincialis, Gentillessee. Rose, single, Rose simple, Rosa berberifolia, Simplicity. Rose, striped, Rose panachï¿½e, Rosa variegata, Warmth of heart. Rose, white, Rose blanche Rosa alba, Silence. Rose, wild, Eglantine, Rosa canina, Poetry. Rose, yellow, Rose jaune, Rosa lutea, Infidelity. Round-leaved Sundew, Rossolis ï¿½ feuilles rondes, Drosera rotundifolia, Surprise, Rue Rue Sauvage, Ruta graveolens, Manners. S. Saffron, Safran, Crocus, Abuse. Sage, Sauge, Salvia, Esteem. Sea-lavender, Staticï¿½ maritim, Statice limonium, Sympathy. Sensitive plant, Sensitive, Mimosa sensitiva, Bashfulness.

Sensitive Hedysarum, Sainfoin oscillant, Hedysarum gyranus, Agitation. Silver-weed, Argentine, Potentilla anserina, Simplicity. Snowball, Boule de neige, Viburnum opulus, Ennui. Snowdrop, Galanth perce-neige, Galanthus nivalis, Consolation. Southernwood, Citronelle, Artemisia abrotanum, Pain. Speedwell, Vï¿½ronique ï¿½lï¿½gante, Veronica amï¿½na, Fidelity. Spindle-tree, Fusain, Evonymus vulgaris, Likeness. Star of Bethlehem, Ornithogale, Ornithogalum, Idleness. Star of Bethlehem, pyramidal, Ornithogale pyramidale, Ornithogalum pyramidale, Purity. Starwort, Astï¿½re, Aster, Afterthought. Strawberry, Fraise, Fragaria, Goodness. Strawberry of the Indies, Fraise de lï¿½Inde, Fragaria indica, Deceitful appearances.

Succory, Chicorï¿½e-amï¿½re, Cichorium intybus, Frugality. Sunflower, (sic) Soleil, (Tournesol) Helianthus, False riches. Sweet Sultan, yellow, Centaurï¿½e-amberboi, Centaurea moschata, Felicity. Sweet William, ï¿½illet de poï¿½te, Dianthus barbatus, Scorn. Syringa, Syringa, Philadelphus. Fraternal regard. T. Tares, Ivraie, Vicia, Vice. Teasel, Cardï¿½re, Dipsacus fullonum, Benefit. Thistle, Chardon, Carduus, Harshness. Thornapple, Datur, Datura stramonium, Deceitful charms. Thornapple, purple, Stramoine fastueuse, Datura fastuosa, Suspicion. Thyme, Thym, Thymus, Activity. Tiger-flower, Tigridie, Tigridia, Cruelty. Toad-flax, Muflier, Antirrhinum, Presumption.

Touch-me-not, Balsamine, Impatiens, Impatience. Tree Primrose, Onagre, ï¿½nothera, Inconstancy. Tuberose, Tubï¿½euse, Polyanthes, Voluptuousness. Tulip Tulipe, Tulipia, Declaration of love. Tulip, virgin, Tulipe vierge, Literary debut. Turnsol, Hï¿½liotrope Heliotropium, The intoxication of love. V. Valerian, red, Valï¿½riane rouge, Valerian rubra, Facility. Violet Ivy, Cobï¿½e grimpante, Cobï¿½a scandens, Knots. Venusï¿½s Looking-glass, Miroir de Venus, Campanula speculum, Flattery. Verain, Verveine, Verbena, Sorcery. Biburnum, prickly, Camara piquant, Lantana aculeata, Severity. Violet, sweet, Violette odorante, Viola odorata, Modesty. Violet, white, Violette blanche, Viola alba, Candor.

Virginian Cowslip, Cyroselle, Dodocatheon meadia, Divinity. Virginian Spiderwort, Ephï¿½mï¿½rine de Virginie, Tradescantia Virginica, Transient felicity. Virginï¿½s-bower, Clï¿½matite, Clematis, Artifice. W. Wake-robin, Arum commun, Arum commune, Ardor. Wall-flower, Giroflï¿½e jaune, Cheiranthus cheiri, Faithful in misfortune. Water-lily, peltated, Nï¿½lumbo, Nymphï¿½a nelumbo, Wisdom. Water-lily, white, Nï¿½nuphar blanc, Nymphï¿½a alba, Eloquence. Water-lily, yellow, Nymphea jaune, Nymphï¿½a lutea, Growing indifference. Weeping-willow, Saule pleureur, Salix babylonica, Sadness. Wheat, Blï¿½, Triticum, Riches. Whortleberry, Airelle myrtille, Vaccinium, Treachery.

Wild Rose-tree, Eglantier, A poetical person. Wild-service, Alisier, Cratï¿½gus terminalis, Harmony. Willow-herb, purple, Salicaire, Lythrum salicaria, Pretension. Windflower, Anï¿½mone, Anemone, Abandonment. Woad, Rï¿½sï¿½da, Reseda, Modest merit. Wood Anemone, Anï¿½mone des prï¿½s, Anemone nemorosa, Sickness. Wood-sorrel, Oxalide-allï¿½luia, Oxalis acetocella, Joy. Wormwood, Absinthe, Absinthium, Absence. Wreath of Roses, Couronne de roses, Corona rosarum, Reward of virtue. Y. Yew If, Taxus, Sadness. Z. Zephyranth, Zï¿½phyranthe, Zephyranthes, Fond Caresses. Microscopes for Sale Accessories, Slides and Kits Protect or even improve your microscope purchase with a carrying case, mechanical stage, video adapters, and lens cleaning kit, books and other supplies...

HST provides name-brand models, like industry-leading National Optical and Swift, and our own HST-brand: the Home series for students, and the 5200 Advanced and 6000 Professional series for more complex lab applications. Shop microscope categories below. How To Use A Microscope: What is a Compound Microscope? This is the most common type of microscope, found in any school or microbiology lab. It's used to greatly magnify tiny specimens like amoebas or thin sections of specimens like leaves or muscle tissue mounted on microscope slides. A compound microscope is ideal for observing cells and cell structure. Almost every student will use a 400x (400-times magnification) compound microscope to study biology. What is a Stereo Microscope? These have lower magnifications of 15 to 45x, and are designed for viewing whole, three-dimensional objects like rocks, insects, flowers, and dissection specimens. They are important for advanced nature studies and ideal for children since an object can be viewed without preparing a slide - simply stick it under the microscope. Terms and Parts of a Compound Microscope This list explains the main parts of your compound microscope and the function of each.

See these parts on the microscope diagram shown below the glossary. Condenser: The light rays from the microscope's illuminator (light) are condensed and focused through this lens in the center of the microscope stage, providing better image resolution. Most 1000x scopes have a built-in, movable 1.25 Abbe condenser underneath the stage. Disc diaphragm or Iris diaphragm: The disc diaphragm is used on most microscopes without 1000x. It's a rotating disc fixed under the stage, designed to provide the best resolution for the objective lens. Turn the disc to the smaller holes when using low magnification (40x to 100x) and to the larger holes for high magnification (400x). Most 1000x models have a fully-adjustable iris diaphragm with an easy, sliding control lever rather than a rotating disc. This type of diaphragm allows you greater control of contrast and helps achieve high image resolution. Eyepiece: The part of the microscope that you look through.

Eyepieces in most compound microscopes have a lens with a 10x magnification level (although you can upgrade with a 15x eyepiece). The National Optical 131 microscope has a pointer built in, which appears as a black line across half of the field of view. To move the pointer, just turn the top of the eyepiece. Field of view: This is the area that's visible when you look through the eyepiece. The greater the magnification used, the smaller the field of view (i.e., FOV at 40x is much greater than at 1000x. This is why you should locate a specimen at lowest power and then gradually narrow your focus as you are increasing magnification). Filter holder and filters: Some microscopes (like our Home 1000x) come with a swing-out filter holder at the bottom of the condenser. Blue and yellow filters can be used to enhance the image in some situations. Focusing: Turning the focus knob or knobs moves the microscope stage up and down to bring the slide sharply into view.

Most microscopes have both fine and coarse focusing, either as two separate knobs or else coaxial (one on top of the other for easy reach). Head: The standard head type is monocular - just one eyepiece. Some microscopes will have a dual head so a teacher and student can view a slide at the same time (it's also convenient for video/digital photography with a digital microscope camera). The most deluxe models have binocular heads for extra-comfortable viewing. Illumination: There are several types of electric lighting for microscopes: Tungsten is the least expensive illumination. It is hotter and less bright than the other kinds. Fluorescent illumination provides cooler and brighter light than tungsten. This is beneficial when viewing slides for long periods of time or observing live specimens, such as protozoa. LED is a bright cool source of light with a bulb that is much longer lasting than a fluorescent bulb. Microscopes with LED lighting typically have a variable control allowing you to change the intensity of light. Halogen provides the very brightest illumination. The best microscopes have halogen lighting and most stereo microscopes with top lighting also use halogen lighting. The intensity of halogen light can be adjusted with a variable control.

Lenses: Standard achromatic lenses help prevent color distortion. Semi-plan or plan lenses improve image quality through superior clarity and flatness. Super high contrast lenses offer extra image contrast so that the image appears much sharper. Magnification: Multiply the magnification of the eyepiece by the magnification the objective lens for the total magnification at that power. If you have a 10x eyepiece and are looking through the 4x objective, the specimen you see is magnified 40x its actual size. Magnification of 400x or 1000x is necessary for studying cells and cell structure. Mechanical stage: This fits onto the stage (in some microscopes it is built in) and provides the best slide control, which makes viewing easier. Clip the slide into place and use the X and Y-axis knobs on the stage to move the slide back and forth under the objective lens. Objective lens: This is second lens of the microscope after the eyepiece. Compound microscopes have a 'nosepiece' with a rotating objective turret, which allows you to change the magnification level for different specimens.

The standard objectives are 4x, 10x, and 40x for total magnification of 40x, 100x, and 400x. DIN is an international standard of lens quality. Oil-immersion objective: Some microscopes have a fourth objective, a 100x oil-immersion lens for 1000x magnification. This allows you to see greater cell detail and cell structure. To use this lens, you need to put 1-2 drops of immersion oil on the slide coverslip. Immersion oil prevents light distortion, so that you can see a sharp image even with the lens pressed right up against the slide. Parcentered: This means that if you centered your slide while using one objective lens, it should still be centered even when you switch to another objective. Parfocal: This means that once you've focused on an object using one objective, the microscope will still be coarsely focused when you switch to a different objective. All you'll have to do is adjust the fine focus a bit. Stage: This is the platform that holds the slide up beneath the objective lens. The stage clips hold the slide in place.

(In some microscopes, these are replaced by a more convenient mechanical stage). Stage stop:This is the small bar and screw between the stage and the arm of the microscope. It prevents the stage from coming too far up, so that the stage can't grind against the objective lens. This is also known as a 'safety rack stop,' and is pre-adjusted by the manufacturer although it can be adjusted by you if need be. Diagram of Compound Microscope Parts Terms and Parts of Stereo Microscopes The following list explains the basic stereo and dissecting microscope parts and functions of each part. Stereo head: Most low-power microscopes have what is called a stereo head, which has two eyepieces - looking through them is something like looking through a pair of binoculars. Some stereo microscopes only have a monocular (single) eyepiece. Eyepiece: This is the part of the microscope that you look through. Eyepieces in stereo microscopes typically have a lens with a 10x magnification level. (You can increase power with a 20x eyepiece upgrade, though.) Both eyepieces have the same magnification on stereo head microscopes.

Diopter: In binocular eyepieces, this compensates for focusing differences between your eyes so you see the image clearly through both eyepieces. Objective lens: The objective lens together with the lens of the eyepiece make up the microscope's magnification. Some stereo microscopes have a rotating objective turret (such as the one pictured below), which allows you to change the magnification level for different specimens; others have a set objective. Stereo microscopes actually have two separate objectives so that each eye is looking through an eyepiece lens as well as an objective lens. Focus knob: Moves the head of the microscope up and down to bring the object sharply into view. Most stereo microscopes have only one focus knob. Lighting: Top lighting shines down and reflects off opaque or solid specimens; bottom lighting shines up through transparent objects. The microscope pictured below has top and bottom lighting, though not all microscopes will have both. Rack and pinion focusing: Most stereo and dissecting microscopes have standard 'rack and pinion' focusing. Turn the focus knob to slide the head of the microscope up and down (closer or farther from the specimen).

Stage clips: These hold microscope slides (which can be viewed under a stereo microscope as long as you don't need to see fine cell details) or other thin objects in place on the stage. Stage plate: Where the specimen is placed for viewing; located directly under the objective lens. Some stereo microscopes have reversible black and white stage plates to provide appropriate contrast with the object being viewed. (Black for light-colored or see-through specimens and white for darker or opaque specimens.) Diagram of Stereo and Dissecting Microscope Parts The diagram below shows where each part is located on a typical stereo microscope. Shop By Category The Microscope Microscopy (This passage was adapted from Microbiology: A Laboratory Manual, 5th edition, Cappuccino, J.S. and Sherman, N., Benjamin/Cummings Science Publishing.) Purposes 1.To become familiar with the history and diversity of microscope instruments. 2.To understand the components, use, and care of the compound brightfield microscope. 3.To learn the correct use of the microscope for observation and measurement of microorganisms. INTRODUCTION Microbiology, the branch of science that has so vastly extended and expanded our knowledge of the living world, owes its existence to Antony van Leeuwenhoek.

In 1673, with the aid of a crude microscope consisting of a biconcave lens enclosed in two metal plates, Leeuwenhoek introduced the world to the existence of microbial forms of life. Over the years, microscopes have evolved from the simple, single-lens instrument of Leeuwenhoek, with a magnification of 300, to the present-day electron microscopes capable of magnifications greater than 250,000. Microscopes are designated as either light microscopes or electron microscopes. The former use visible light or ultraviolet rays to illuminate specimens. They include brightfield, darkfield, phase-contrast, and fluorescent instruments. Fluorescent micro-scopes use ultraviolet radiations whose wavelengths are shorter than those of visible light and are not directly perceptible to the human eye. Electron microscopes use elec-tron beams instead of light rays, and magnets instead of lenses to observe submicro-scopic particles. Essential Features of Various Microscopes Brightfield Microscope This instrument contains two lens systems for magnifying specimens: the ocular lens in the eyepiece and the objective lens located in the nose-piece.

The specimen is illuminated by a beam of tungsten light focused on it by a sub-stage lens called a condenser, and the result is that the specimen appears dark against a bright background. A major limitation of this system is the absence of contrast between the specimen and the surrounding medium, which makes it difficult to observe living cells. Therefore, most brightfield observations are performed on nonviable, stained preparations. Darkfield Microscope This is similar to the ordinary light microscope; however, the condenser system is modified so that the specimen is not illuminated directly. The con-denser directs the light obliquely so that the light is deflected or scattered from the spec-imen, which then appears bright against a dark background. Living specimens may be observed more readily with darkfield than with brightfield microscopy. Phase-Contrast Microscope Observation of microorganisms in an unstained state is possible with this microscope. Its optics include special objectives and a condenser that make visible cellular components that differ only slightly in their refractive indexes. As light is transmitted through a specimen with a refractive index different from that of the surrounding medium, a portion of the light is refracted (bent) due to slight varia-tions in density and thickness of the cellular components.

The special optics convert the difference between transmitted light and refracted rays, resulting in a significant vari-ation in the intensity of light and thereby producing a discernible image of the struc-ture under study. The image appears dark against a light background. Fluorescent Microscope This microscope is used most frequently to visualize speci-mens that are chemically tagged with a fluorescent dye. The source of illumination is an ultraviolet (UV) light obtained from a high-pressure mercury lamp or hydrogen quartz lamp. The ocular lens is fitted with a filter that permits the longer ultraviolet wavelengths to pass, while the shorter wavelengths are blocked or eliminated. Ultraviolet radiations are absorbed by the fluorescent label and the energy is re-emitted in the form of a different wavelength in the visible light range. The fluorescent dyes absorb at wavelengths between 230 and 350 nanometers (nm) and emit orange, yellow, or greenish light. This microscope is used primarily for the detection of antigen-antibody reactions. Antibodies are conjugated with a fluorescent dye that becomes excited in the presence of ultraviolet light, and the fluorescent portion of the dye becomes visible against a black background.

Electron Microscope This instrument provides a revolutionary method of microscopy, with magnifications up to one million. This permits visualization of submicroscopic cel-lular particles as well as viral agents. In the electron microscope, the specimen is illu-minated by a beam of electrons rather than light, and the focusing is carried out by elec-tromagnets instead of a set of optics. These components are sealed in a tube in which a complete vacuum is established. Transmission electron microscopes require speci-mens that are thinly prepared, fixed, and dehydrated for the electron beam to pass freely through them. As the electrons pass through the specimen, images are formed by direct-ing the electrons onto photographic film, thus making internal cellular structures visi-ble. Scanning electron microscopes are used for visualizing surface characteristics rather than intracellular structures A narrow beam of electrons scans back and forth, producing a three-dimensional image as the electrons are reflected off the specimen's surface. While scientists have a variety of optical instruments with which to perform routine laboratory procedures and sophisticated research, the compound brightfield micro-scope is the "workhorse" and is commonly found in all biological laboratories.

Although you should be familiar with the basic principles of microscopy, you probably have not been exposed to this diverse array of complex and expensive equipment. Therefore, only the compound brightfield microscope will be discussed in depth and used to examine specimens. To become familiar with the: 1.Theoretical principles of brightfield microscopy. 2.Component parts of the compound micro-scope. 3.Use and care of the compound microscope. 4.Practical use of the compound microscope for visualization of cellular morphology from stained slide preparations. PRINCIPLE Microbiology is a science that studies living organisms that are too small to be seen with the naked eye. Needless to say, such a study must involve the use of a good compound microscope. Although there are many types and variations, they all fundamentally consist of a two-lens system, a variable but controllable light source, and mechanical adjustable parts for determining focal length between the lenses and specimen. Stage A fixed platform with an opening in the center allows for the passage of light from an illu-minating source below to the lens system above the stage. This platform provides a surface for the placement of a slide with its specimen over the central opening.

In addition to the fixed stage, most microscopes have a mechanical stage that can be moved vertically or horizontally by means of adjustment controls. Less sophisticated micro-scopes have clips on the fixed stage, and the slide must be positioned manually over the central opening. Illumination The light source is positioned in the base of the instrument. Some microscopes are equipped with a built-in light source to pro-vide direct illumination. Others are provided with a mirror; one side flat and the other concave. An external light source, such as a lamp, is placed in front of the mirror to direct the light upward into the lens system. The flat side of the mirror is used for artificial light, and the concave side for sunlight. Abbe Condenser This component is found directly under the stage and contains two sets of lenses that collect and concentrate light passing upward from the light source into the lens sys-tems. The condenser is equipped with an iris diaphragm, a shutter controlled by a lever that is used to regulate the amount of light entering the lens system. Body Tube Above the stage and attached to the arm of the microscope is the body tube. This structure houses the lens system that magnifies the specimen.

The upper end of the tube contains the ocular or eyepiece lens. The lower portion consists of a movable nosepiece containing the objective lenses. Rotation of the nosepiece posi-tions objectives above the stage opening. The body tube may be raised or lowered with the aid of coarse-adjustment and fine-adjustment knobs that are located above or below the stage, depending on the type and make of the instrument. Theoretical Principles of Microscopy To use the microscope efficiently and with minimal frustration, you should understand the basic principles of microscopy: magnification, resolution, numerical aperture, illumination, and focusing. Magnification Enlargement or magnification of a specimen is the function of a two-lens system; the ocular lens is found in the eyepiece, and the objective lens is situated in a revolving nose-piece. These lenses are separated by the body tube. The objective lens is nearer the specimen and magnifies it, producing the real image that is projected up into the focal plane and then magnified by the ocular lens to produce the final image. The most commonly used microscopes are equipped with a revolving nosepiece containing four objective lenses possessing different degrees of magnification.

When these are combined with the magnification of the ocular lens, the total or overall linear magnification of the specimen is obtained. Resolving Power or Resolution Although magnification is important, you must be aware that unlimited enlargement is not possible by merely increasing the magnifying power of the lenses or by using additional lenses, because lenses are limited by a property called resolving power. By definition, resolving power is the ability of a lens to show two adjacent objects as discrete entities. When a lens cannot discriminate, that is, when the two objects appear as one, it has lost resolu-tion. Increased magnification will not rectify the loss, and will, in fact, blur the object. The resolv-ing power of a lens is dependent on the wave-length of light used and the numerical aperture, which is a characteristic of each lens and imprinted on each objective. The numerical aper-ture is defined as a function of the diameter of the objective lens in relation to its focal length. It is doubled by use of the substage condenser; which illuminates the object with rays of light that pass through the specimen obliquely as well as directly.

Thus, resolving power is expressed mathematically, as follows: Resolving power = Wavelength of Light . 2 (Numerical Aperture) Based on this formula, the shorter the wave-length, the greater the resolving power of the lens. Thus, short wavelengths of the electromag-netic spectrum are better suited than longer wavelengths in terms of the numerical aperture. However; as with magnification, resolving power also has limits. You might rationalize that merely decreasing the wavelength will automati-cally increase the resolving power of a lens. Such is not the case, because the visible portion of the electromagnetic spectrum is very narrow and borders on the very short wavelengths found in the ultraviolet portion of the spectrum. The relationship between wavelength and numerical aperture is valid only for increased resolving power when light rays are parallel. Therefore, the resolving power is dependent on another factor, the refractive index. This is the bending power of light passing through air from the glass slide to the objective lens. The refractive index of air is lower than that of glass, and as light rays pass from the glass slide into the air, they are bent or refracted so that they do not pass into the objective lens.

This would cause a loss of light, which would reduce the numerical aperture and diminish the resolving power of the objective lens. Loss of refracted light can be compensated for by interposing mineral oil, which has the same refractive index as glass, between the slide and the objective lens. In this way, decreased light refraction occurs and more light rays enter directly into the objective lens, producing a vivid image with high resolution. Illumination Effective illumination is required for efficient magnification and resolving power. Since the intensity of daylight is an uncontrolled variable, artificial light from a tungsten lamp is the most commonly used light source in microscopy. The light is passed through the con-denser located beneath the stage. The condenser contains two lenses that are necessary to produce a maximum numerical aperture. The height of the condenser can be adjusted with the con-denser knob. Always keep the condenser close to the stage, especially when using the oil-immersion objective. Between the light source and the condenser is the iris diaphragm, which can be opened and closed by means of a lever; thereby regulating the amount of light entering the condenser. Excessive illumination may actually obscure the specimen because of lack of contrast.

The amount of light entering the microscope differs with each objec-tive lens used. A rule of thumb is that as the mag-nification of the lens increases, the distance between the objective lens and slide, called working distance, decreases, whereas the numerical aperture of the objective lens increases. Use and Care of the Microscope You will be responsible for the proper care and use of microscopes. Since microscopes are expensive, you must observe the following regu-lations and procedures. The instruments are housed in special cabinets and must be moved by users to their laboratory benches. The correct and only acceptable way to do this is to grip the microscope arm firmly with the right hand and the base with the left hand, and lift the instrument from the cabinet shelf. Carry it close to the body and gently place it on the laboratory bench. This will prevent collision with furniture or co-workers and will protect the instrument against damage. Once the microscope is placed on the laboratory bench, observe the following rules: 1.Remove all unnecessary materials such as books, papers, purses, and hats from the laboratory bench. 2.Uncoil the microscope's electric wire and plug it into an electrical outlet.

3.Clean all lens svstems; the smallest bit of dust, oil, lint, or eyelash will decrease the efficiency ot the microscope. The ocular; scan-ning, low-power, and high-power lenses may be cleaned by wiping several times with acceptable lens tissue. Never use paper tow-eling or cloth on a lens surface. If the oil-immersion lens is gummy or tacky, a piece of lens paper moistened with methanol is used to wipe it clean. If the lens is very dirty it may be cleaned with xylol however the xylol cleansing procedure should be performed only by the instructor, and only if necessary. Consistent use of xylol may loosen the lens. The following routine procedures must be followed to ensure correct and efficient use of the microscope while focusing. 1. Place the microscope slide with the specimen within the stage clips on the fixed stage. Move the slide to center the specimen over the opening in the stage directly over the light source. 2. Rotate the scanning lens or the low power lens into position. While watching from the side to insure that the lens doesn't touch the specimen, turn the coarse focus knob to move the stage as close as it can get to the lens without touching the lens.

(Always watch from the side whenever you move a specimen towards any objective lens to make sure the lens doesn't crash through the specimen and get damaged!) 3. Now, while looking through the ocular lens, turn the coarse focus knob carefully, and slowly move the stage away from the lens until the specimen comes into vague focus. Then, use the fine focus knob to bring the specimen into sharp focus. 4. If this is the first specimen of the day, you should Kohler your microscope at this point (while it is in focus). Otherwise, if your microscope has already been Kohlered you won't need to do it again 5. Routinely adjust the light source by means of the light source transformer setting, and/or the iris diaphragm, for optimum illumination for each new slide and for each change in magnification. 6. Our microscopes are parfocal, which means that when one lens is in focus, other lenses will also have the same focal length and can be rotated into position without further major adjustment. In practice, however; usually a half-turn of the fine-adjustment knob in either direction is necessary for sharp focus. 7.

Once you have brought the specimen into sharp focus with a low-powered lens, preparation may be made for visualizing the spec-imen under oil immersion. Place a drop of oil on the slide directly over the area to be viewed. Rotate the nosepiece until the oil-immersion objective locks into position. Care should be taken not to allow the high-power objective to touch the drop of oil.The slide is observed from the side as the objective is rotated slowly into position. This will ensure that the objective will be properly immersed in the oil. The fine-adjustment knob is readjusted to bring the image into sharp focus. 8. During microscopic examination of microbial organisms, it is always necessary to observe several areas of the preparation. This is accomplished by scanning the slide with-out the application of additional immersion oil. This will require continuous, very fine adjustments by the slow, back-and-forth rotation of the fine adjustment knob only. On completion of the laboratory exercise, return the microscope to its cabinet in its original condition. The following steps are recommended: 1.Clean all lenses with dry, clean lens paper. If you need to, you can use a drop or two of methanol to help clean the lens. Use xylol to remove oil from the stage only.

2. Place the low-power objective in position and bring the stage and objectives close together. 3.Center the mechanical stage. 4.Coil the electric wire around the body tube and the stage. 5.Carry the microscope to its position in its cabinet in the manner previously described.

Question: Which flower has the same name as a diaphragm in the eye?
Answer: Iris