Sample Article:
What You Need To Know About
The Kellner Telescopic Eyepieces
- Kellner eyepieces are designed to use a combination of concave and convex lenses.
- When put together the lenses produce eyepieces that are able to correct and reduce chromatic aberration.
- The eyepieces produce much clearer and sharper images than the simple lens by designed Ramsden
Chromatic Aberration
Chromatic aberration or colour distortion happens when the glass lens used does not bring all the colours to the same focal point. The resulting effect is blurry images similar to the rainbow.
- This is because there are different wavelengths of light on any given lens. For example the wavelength of a blue light does not focus to the same flat surface or plane as the wavelength of a red light. The longer the wavelength, the lesser the relative speed of light (Refractive index).
- The work of achromatic lenses such as the Kellner eyepiece is to focus the different. wavelengths of light on to the same flat surface in order to improve colour.
- The technique of attaching together two lenses with varying refractive index results in what is called a doublet lens.
- The Kellner eyepiece is the first known achromatic doublet. Its design uses three elements grouped in to two as follows;
1. achromatic doublet eye lens
2. plano convex field lens.
The resulting output is sharper and brighter images at low to medium power. Their main drawback is that there are internal reflections. These can be easily corrected with anti- reflection coating.
Achromatic Doublet Eye Lens
The doublet consist of a concave and a convex glass lens being cemented together to become an image magnifier. The two lenses when attached together become the doublet. One lens acts to eliminate distortions from the other lens and vice versa.
Features of an achromatic doublet
- A Concave Lens made of flint glass: Flint glass has high refractive index. Meaning that the speed of light travelling through is comparatively higher than other types of glass lenses.
- Flint glass also combines a low Abbe Number. Generally an Abbe number is the measure of distortion of a material in relation to the speed of light (refractive Index). Abbe Number, is also known as the V-number or Constrigence.
- A Convex Lens made from Crown Glass. Crown glass has a low refractive index and a low Abbe Number. This means that light travels relatively slowly and the rate of distortion is low.
- Plano Convex lens Located near the image field, the plano convex lens has one flat lens (plano) and the other is curved (convex).
Kellner eyepieces provide quality images at a comparatively cheap price. They have an apparent field of view that ranges between 40 – 50 degrees. At 17 degrees angular field and 15mm field stop, the lenses are considered useful on small and medium telescopes.
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Sample Article: The A,B,C of Fire - How to Identify and fight a Fire
Panic is usually the instinctive reaction of most people when faced with a breakout of fire. A sudden fire can be unerving especially when you do not know how to deal with it.
In this article you will learn about the following;
- What causes fire
- Types of fire
- How to extinguish a fire
In order for a fire to burn, three elements must exist. these are;
- Oxygen
- Fuel
- Heat
Types of Fire
Fire is classified according to the main combustible or flammable material burning. However, when for example burning gas causes wood and cloth to burn, a fire extinguisher with combined properties is used to put out the fire.
There are four main classifications of fire as set out below;
Class A
This is the most common type of fire. Burning wood,paper, cloth, and rubbish fall in this category.
The fire Extinguisher marked A is to be used in such a fire.
Class B
Flammable gases and liquids such as cooking gas, paint, petrol/gasoline and oil fall here.
The Fire Extinguisher to use for such fires is marked A,B
Class C
This type of fire involves burning electrical wires, cables, as well as electrical equipment.
The danger of getting an electric shock during such a fire is real. It is important to avoid touching electricity conductors qhwn the power supply is on. The first thing you must do is switch of the main power supply.
A,B,C fire extinguishers are used in this type of fire.
Class D
This type of fire is found in factories dealing with industrial chemicals and metal alloys. It is useful to note that the fire extinguisher to reach for is the one marked A,C
How to Extinguish a Fire
The Acronym to remember when putting out a fire is P.A.S.S. Think of it as an exam you need to pass.
The procedure is very simple as set out below:
P Pull the the pin that locks the extinguisher at the top
A Aim the nozzle of the extinguisher at the base of the fire
S Squeeze the handle of the extinguisher to eject the extinguishing agent
S Spread the extinguishing agent at the base of the fire
The easiest way to put out this type of fire is to switch of the main power supply. .
Always remember to ;
- first asses whether a fire is small enough for you to handle. If not, evacuate the area calmly but quickly.
- Always fight a fire with your back to the nearest exit
- should your clothes catch fire, immediately drop to the ground and roll until the flames die The easiest
- Identifying and classifying a fire
- Using the appropriate fire extinguisher for each fire
- Fighting a small fire
Burns are usually categorised according to the damage they cause to the skin tissue. First Degree Burns are also referred to as Superficial burns which cause painful damage to the top layer of skin. Second and third degree burns affect the second and third layers respectively.
First and most second degree burns can be treated at home. here is what you need to do;
- Cool the burn with cold preferably running water for atleast ten minutes or until the burning pain dissipates. This will stop theheat from the burn from further damaging the inner tissue of the skin
- Soak the burn in cold whole milk for up to 15 minutes then thoroughly rinse out your skin.
- Soothe the burn with home remedies such as camomille Tea bags, Aloe Vera, Lemon Juice, Lavendar Oil, and dilute vinegar. These remedies contain antiseptic and/or soothing properties.
- If the burn is an open wound, use steralised gauze or cling film to cover the wound. Be sure not to bind the wound tightly to allow for circulation.
Do Not :
- Puncture a blister as this opens up the wound which may cause it to fester and take longer to heal
- Apply greasy oil which only traps the heat inside the skin and makes the burn worse.
