The Microscope

Compound Microscope Uses multiple lenses to: Collect light from the sample Then a separate set of lenses to focus the light into the eye or camera Heavier, larger, and more expensive than simple microscopes due to the increased number of lenses used in construction

Compound Microscope

Advantage of Multiple Lenses Improved Numerical Aperture Reduced Chromatic Aberration Exchangeable objective lenses to adjust the magnification Has the ability to change the amount of light that is on the specimen

Improved Numerical Aperture Consenser: an opening through which light travels You can change the width of the condenser More narrow: the light rays are more collected Sharp focus onto the image plan More wide: rays are more dispersed Focus is sharp around what the lens is focusing on and blurred towards the perimeter

Reduced Chromatic Aberration Chromatic aberration distortion in which there is a failure of a lens to focus all colors This occurs because the lenses have a different refractive index for different wavelengths of light Refractive index – bending of light

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 observed Regulates the amount of light that passes through the condenser

Limitation of Multiple Lenses Cannot distinguish between objects that are less than 0.2 μm apart – the images are seen fused together This is called the Resolution

Condenser Iris Diaphragm

Resolution The ability to discriminate between two close objects as separate

Resolving power is determined by the amount and physical properties of the visible light that enters the microscope The more light that enters the objective lens, the greater the resolution The size of the aperture (opening) of the lens decreases with increasing magnification, allowing less light to enter the objective So you will need to increase the light intensity at the higher magnifications

How to properly carry a microscope Upright One hand on its arm One hand supporting its base Avoid swinging and jarring when setting it down

How to Clean the Lens Special grit-free lens paper Use circular motion to wipe the lens Clean ALL lenses before and after use

Always begin focusing with the lowest-power objective (10x) objective lens in position, changing to the higher power as necessary.

Wet Mounts Used to look at cells and tissues Mix the cells with physiologic saline Can stain with methylene blue Always use a coverslip with temporary (wet mount) preparations.

Returning the microscope to the storage cabinet: Remove the slide from the stage Rotate the lowest-power objective lens into position Wrap the cord neatly around the base Replace the dust cover or return the microscope to the appropriate storage area

Never remove any parts from the microscope; inform your instructor of any mechanical problems that arise.

Magnification Two lenses that magnify: Ocular Objective: Magnifies the specimen to produce a real image The real image is projected to the ocular The real image is then magnified even further by the ocular to produce the virtual image

Total Magnification Total Magnification = Objective lens power * Ocular lens power So if: Ocular = 10x Objective = 45x Total Magnification =

Total Magnification Total Magnification = Objective lens power * Ocular lens power So if: Ocular = 10x Objective = 45x Total Magnification = 10 * 45 = 450

Diameter of a Microscopic Field As you increase magnification, the field decreases Knowing the field size can tell you the size of your specimen

You can determine the size of the field: Diameter field A * Total magnification field A = Diameter field B * Total magnification fieldB Diameter field B = (diameter field A * Total magnification field A)/Total mag Field B