Microbiology Lab Practical 1: Microscope

3 Lenses on a Light Microscope

1. Ocular lens

2. Objective lens

3. Your eyes

Eyepieces (Ocular Lenses)

Lens that the viewer looks through. Contains a lens that magnifies about 10x

Objective Lenses

4 pieces that have various magnification powers from 4x, 10x, 40x, & 100x.

Fine and Course Adjustment Knobs Function

Used to visualize the sample.

Fine Focus Knob

Fine tunes the focus, increases the detail.

Coarse Focus Knob

Brings specimen into general focus.

Condenser

Focuses the concentration of light.

Iris Diaphragm

Adjusts the amount of light.

Observation Tube

Connects the eyepiece to the objective lenses.

Revolving Nose Piece

Rotating turret that houses the objective lenses.

Stage

Platform where you put the slide.

Slide Clip

Metal piece that holds the slide in place.

Microscope Frame

The part that connects the observation tube to the stage as well as the rest of the microscope.

Arm

Connects the eyepiece to the base.

Base

Bottom part of the microscope that contains the light source & supports the microscope

Abbe's Equation Definition

Demonstrates how immersion oil works to improve resolution.

Abbe's Equation

(mathematical resolution definition)

d = 0.61(λ) wavelength / nSin𝜃

Layman's Definition of Resolution

The shortest distance between two objects where one can still discern two distinct objects.

d stands for?

Minimal Distance

λ stands for?

Wavelength / Visible light

0.61 stands for?

Constant (always there)

nSin𝜃 stands for?

Angle of Refraction

Do you want resolution or "d" to be a small or large number?

Small (10/5=2)

How to decrease the resolution?

Increase the denominator

How do you achieve an improvement in resolution when you increase your magnification to 1000 times?

Immersion oil on the 100x objective lens works to improve resolution when the magnification is increased to 1000 times.

What is total magnification and how do we calculate it?

Total magnification is ocular lens x objective lens.

Calculate the total magnification of 4x.

4x * 10x = 40x

Calculate the total magnification of 10x.

10x * 10x = 100x

Calculate the total magnification of 40x.

40x * 10x = 400x

Calculate the total magnification of 100x (oil).

100x (oil) * 10x = 1000x

What is the difference between the iris diaphragm and the condenser on a light microscope in terms of managing light?

The condenser focuses the concentration of light through the specimen. The iris diaphragm controls the amount of light passing through the specimen.

Increase the Magnification

Loses clarity or resolution of an image.

If you increase in magnification, what do you generally have to do with your light? (2)

The light intensity decreases as magnification increases. Higher magnification means the light is bent more. At a certain point, the light is bent so much that it can't make it through the objective lens. You have to perform oil immersion with your light.

If you increase in magnification, what do you generally have to do with your light? (1)

Increase the brightness of bulb.

Oil Immersion (1)

At 100x you'll need to put a drop of oil between your specimen and the objective lens. The oil "unbends" the light to stretch out the working distance and make it possible to image at high magnifications.

Oil Immersion (2)

It increases the angle of aperture or the light rays and focuses the light into the specimen.

1. What is the total magnification when viewing a sample using the 40X objective lens?

Ocular lens 10x *x* Objective lens 40x = 400x

2. How does a condenser affect light compared to the iris diaphragm?

Condenser = Focuses whole light.

vs.

Iris Diaphragm = Controls amount of light.

3. When you increase magnification do you generally have to increase or decrease light?

The light intensity decreases as magnification increases.

4. What is the layman's definition of resolution?

Shortest distance between two objects where one can still discern two distinct objects.

5. How does immersion oil improve resolution?

It increases the angle of aperture and/or the light rays.

6. When you looked at the prepared slides were larger organisms best viewed at higher or lower magnification?

Larger organisms were best viewed at lower magnification because it has the largest field of view compared to higher magnification where the field of view closes in.