Guide to the practical teaching
of biology and genetics

Dry objectives, centring the objects, iris diaphragm function

TASK 1: Arranging the object in the visual field

Permanent preparation (PP) of a letter - "písmeno"

Put the permanent preparation with a block letter on the stage of microscope to be able to read the word (not reversed). Draw one asymmetrical letter (a, e, y, k...) using the smaller magnification of the objective (4×). What image can you see in the microscope?

TASK 2: Arranging the object using different magnifications 4×, 10×, 40×

PP: insect wing - "křídlo hmyzu" (or letter)

Observe the specimen under different magnifications. How does the free working distance, visual field size and resolution change based on magnification used?

Fig.: Different magnifications of objective (A - 4×, B - 10×, C - 40×) and visual field (insect wing).

TASK 3: The function of iris diaphragm

PP: feather - "prachové peří"

Observe the feather under different objectives (4×, 10× a 40×) with an opened and closed iris diaphragm. What is the difference and what principle arises from this observation?

TASK 4: Centring the object

PP: stained wool - "vlna barvená"

Place the stained wool (cross of fibers or other characteristic point) in the centre of the visual field under the smallest magnification (4×). Then use the 10× magnifying objective without drifting the object and observe the wool. Can you see some change? (Do the same with 40× magnifying objective). What principle arises from this observation?

Fig.: Centring the object (stained wool) and different magnification of objectives (A - 4×, B - 10×, C - 40×).