Polaroid MicroCam manual Microscope parts, Koehler illumination

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Microscope parts (17)

aPhototube eyepiece

bPhototube

cViewing eyepiece

dRevolving nosepiece

eObjective lens

fSpecimen

gSpecimen stage

hSubstage condenser

iAperture diaphragm adjustment

jCondenser centering screws

kField diaphragm adjustment

lField diaphragm

mCondenser focusing knob

nCoarse and fine focusing knobs

oLamp

pLamp voltage control

Filter placement

Filters should be placed in the filter holder (18-q) if the microscope has one. Alternatively, they can be placed where the light exits from the microscope base (18-r). If the latter location is used, be sure the filters are clean and undamaged. The nearer they are to the field diaphragm, the more likely any blemishes on the filter will be focused with the specimen.

The addition of certain color filters may change the effective focus of the microscope (depending on the optical characteristics of the objective lens). After adding filters, re-focus the image before taking pictures.

Koehler illumination

Most modern compound microscopes are designed for Koehler illumination, which is ideal for photomicrography. This technique involves proper alignment of the light source, alignment and focus of the substage condenser (17-h) and field diaphragm (17-l), and adjustment of the aperture diaphragm (17-i). Koehler illumination provides even lighting and, in addition, enables the objective lens to produce optimum resolution.

Alignment and focus of the substage condenser and the field diaphragm

1Place a specimen on the stage and focus it accurately. Slowly close the aperture diaphragm of the substage condenser to a point where you see a distinct reduction in brightness through the eyepiece. (See also Adjusting the aperture diaphragm.)

2Close the field diaphragm to its smallest setting. Viewing through the eyepiece, raise or lower the substage condenser until the edge of the field diaphragm is sharply focused with the specimen image (19).

3Open the field diaphragm to about 3/4 of the visual field and refocus the edge of the diaphragm, as above (20).