2 Compound Microscope Uses multiple lenses to: Collect light from the sampleThen a separate set of lenses to focus the light into the eye or cameraHeavier, larger, and more expensive than simple microscopes due to the increased number of lenses used in construction
4 Advantage of Multiple Lenses Improved Numerical ApertureReduced Chromatic AberrationExchangeable objective lenses to adjust the magnificationHas the ability to change the amount of light that is on the specimen
5 Improved Numerical Aperture Consenser: an opening through which light travelsYou can change the width of the condenserMore narrow: the light rays are more collectedSharp focus onto the image planMore wide: rays are more dispersedFocus is sharp around what the lens is focusing on and blurred towards the perimeter
6 Reduced Chromatic Aberration Chromatic aberration distortion in which there is a failure of a lens to focus all colorsThis occurs because the lenses have a different refractive index for different wavelengths of lightRefractive index – bending of light
7 Has the ability to change the amount of light that is on the specimen Iris Diaphragm: allows the different refractive indexes of the specimen to be observedRegulates the amount of light that passes through the condenser
8 Limitation of Multiple Lenses Cannot distinguish between objects that are less than 0.2 μm apart – the images are seen fused togetherThis is called the Resolution
11 ResolutionThe ability to discriminate between two close objects as separate
12 Resolving power is determined by the amount and physical properties of the visible light that enters the microscopeThe more light that enters the objective lens, the greater the resolutionThe size of the aperture (opening) of the lens decreases with increasing magnification, allowing less light to enter the objectiveSo you will need to increase the light intensity at the higher magnifications
13 How to properly carry a microscope UprightOne hand on its armOne hand supporting its baseAvoid swinging and jarring when setting it down
14 How to Clean the Lens Special grit-free lens paper Use circular motion to wipe the lensClean ALL lenses before and after use
15 Always begin focusing with the lowest-power objective (10x) objective lens in position, changing to the higher power as necessary.
16 Wet MountsUsed to look at cells and tissuesMix the cells with physiologic salineCan stain with methylene blueAlways use a coverslip with temporary (wet mount) preparations.
17 Returning the microscope to the storage cabinet: Remove the slide from the stageRotate the lowest-power objective lens into positionWrap the cord neatly around the baseReplace the dust cover or return the microscope to the appropriate storage area
18 Never remove any parts from the microscope; inform your instructor of any mechanical problems that arise.
19 Magnification Two lenses that magnify: Ocular Objective: Magnifies the specimen to produce a real imageThe real image is projected to the ocularThe real image is then magnified even further by the ocular to produce the virtual image
20 Total MagnificationTotal Magnification = Objective lens power * Ocular lens powerSo if:Ocular = 10xObjective = 45xTotal Magnification =
22 Diameter of a Microscopic Field As you increase magnification, the field decreasesKnowing the field size can tell you the size of your specimen
23 You can determine the size of the field: Diameter field A * Total magnification field A = Diameter field B * Total magnification fieldBDiameter field B = (diameter field A * Total magnification field A)/Total mag Field B