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2023-06-02 20:11:22 How do we use lenses?

Concave Lens is used:
to correct myopia eye defects
to make spectacles
in peepholes in hotel room doors.
in the construction of certain types of telescopes.

Convex Lens is used:
to correct hypermetropia eye defects
in cameras and digital cameras as optical devices for producing a reduced, true, and inverted image on film.
in microscopes and telescopes
to produce a magnified image of an object.

Subtypes of convex lens are:
A bi-convex lens is a basic lens that consists of two convex surfaces in a spherical form with the same radius of curvature.
Plano-convex lenses are positive focal length elements that have one spherical surface and one flat surface
ConConvex lenses are also known as converging lenses since the rays converge after falling on the convex lens.

Subtypes of concave lenses are:
A bi-concave lens have two inward curved surfaces. These lenses have a negative focal length.
A plano-concave lens is an optical lens with one concave surface and one flat surface. It has a negative focal length and can be used for light projection, beam expansion, or to increase the focal length of an optical system.
A concavo-convex lens is a converging lens. This is because it is thicker in the middle and thinner at the edges allowing it to converge all the light that is incident on it.

The lens of our eyes is also convex. The inverted image of the item on the retina is formed by the eye lens.

3.5K views17:11
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2023-06-01 16:25:12
What is a lens and its types?

A lens is a piece of transparent material that is shaped to bend light rays in a specific way as they pass through it, whether that means causing the rays to converge to or diverge from a specific point.
The word “lens” derives from the Latin word “lentil,” owing to the shape similarities between a converging lens and a legume.

The types of lenses are:

concave lenses with following features
The light is spread out by a diverging lens.
Thinner in the centre than at the edges.
The image is on one side of the lens, while the object is on the other.
The focal length is positive.
The image will be erect, virtual, and diminished.


convex lenses with following features
The refracted rays are converged by a converging lens.
Thicker in the centre than at the edges.
The object and the image are both on the same side of the lens.
The focal length is negative.
The resultant image will be both real and inverted.

4.1K views13:25
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2023-05-31 20:29:09
What is a brief history of sunglasses?

The first sunglasses were invented sometime in 12th century China. They were a crude slab of smoked quartz that was made to block out the light from the sun. The frames were roughly shaped frame to hold them against the user's face.

Around 1430 vision-correcting eyeglasses were darkened and they were introduced into Italy via the Chinese.

In the 18th century, an English optician James Ayscough began experimenting with tinted lenses in spectacles but not to protect from the sun but to improve vision for those with poor or failing eye sight. He believed that by changing the color of the lenses to a blue/green tint, he could correct specific vision impairments.

The modern-type sunglasses appeared in the 20th century. In 1929, a US businessman Sam Foster, put sunglasses into mass production in America.

Since 1970s well-known fashion designers and movie stars escalated the sunglass craze with their brand-name lines.

4.1K views17:29
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2023-05-31 11:18:11
How progressive lenses were invented ?

The first patent for a design of progressive addition lenses (PAL) was obtained by Owen Aves in England in 1907. However, because of the limitations in manufacturing in those times, he was never able to produce and commercialize such lenses.

In the first half of the 20th century some other designs for progressive lens were patented but never successfully commercialized.

The first progressive with a modern design was patented by Bernard Maitenaz of France, in 1953.

The progressive lens has been evolving since then, with the help of manufacturers to improve usability and distortion-free viewing.

Progressive lenses are a giant leap in lens technology since they allow the wearer the ability to see distance, intermediate, and near fields all in one set of eyewear. This is especially helpful for viewing digital devices since they reside in the intermediate range, which distance and bifocal eyeglasses cannot reach .

4.2K views08:18
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2023-05-30 12:03:16
Who invented bifocals?

The first eyeglasses could only be used to rectify hyperopia or presbyopia, the eyeglasses for myopia appeared later. But there had been no single solution to help those who suffered from both types of vision impairments until 1784.

American polymath Benjamin Franklin is credited for inventing bifocals in 1784. He created them because he was tired of switching eyeglasses for far and near. Therefore, he combined the two lenses by cutting them and then combining the segments into one glass with a sharp switch between the upper and lower lenses.

In the 19th century, Louis de Wecker, a French ophthalmologist, helped to improve the original model by fusing the upper and lower sections.

Peter Williams, who invented trifocal lenses, is known for coining the term “bifocals” in 1824, although he credited Benjamin Franklin for the invention.

5.0K views09:03
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2023-05-29 18:14:12
How did the first wearable eyeglasses look like?

Most historians believe that the first form of eyeglasses was produced in Italy by monks or craftsmen around 1285-1289. These magnifying lenses for reading were shaped like two small magnifying glasses and set into bone, metal, or leather mountings that could be balanced on the bridge of nose.

The first known artistic representation of the use of eyeglasses was Tommaso da Modena's painting in 1352, depicting monks reading and writing manuscripts . One monk uses a magnifying glass, but another wears glasses perched on his nose .

Later, the first eyeglass frame temples were made by Spanish craftsmen in 1600s. They affixed ribbons of silk or strings to the frame and looped them over the user's ears.

The modern style of eyeglasses frame, which could be placed over the ears and nose, was invented in the 18th century in England. These early eyeglasses had glass lenses set into heavy frames of wood, lead or copper.

5.0K views15:14
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2023-05-28 19:06:40
When did humans start to improve vision?

Scientists suppose that the first vision aid, called a reading stone, was invented around 1000 AD. The reading stone was a glass sphere that was laid on top of the reading material to magnify the letters.

One of the earliest historical reference to magnification dates back to ancient Egyptian hieroglyphs in the 5th century BC, which depict "simple glass meniscal lenses".

The written record of magnification also dates back to the 1st century AD, when Seneca the Younger, a tutor of Emperor Nero of Rome, wrote: "Letters, however small and indistinct, are seen enlarged and more clearly through a globe or glass filled with water". Nero is also said to have watched the gladiatorial games using an emerald as a corrective lens .

According to researchers, spectacles were invented more than 1000 years ago in ancient China and were in widespread consumer use in by the Chinese Imperial family, aristocrats and rich civilians.

5.6K views16:06
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2023-05-25 15:30:01
Who are much more venomous than land-based snakes?

Sea snakes are far more venomous than land snakes, including the Inland Taipan.

Being underwater the venom gets diluted, so it has to be more potent.

Just 1.5 mg of venom from the hook-nosed sea snake (Enhydrina schistosa) is estimated to be enough to kill 22 people. This one of the most venomous snake in the world is found in the ocean off Australia, New Zealand, and Asia. They grow to mature lengths up to 1.5 meters (3-5 feet) and weigh in at up to 1.8 kg (4 pounds).

Also known as the Faint-Banded Sea Snake, the Belcher’s Sea Snake (Hydrophis belcheri) is also extremely venomous. According to some studies, its venom is 100 times stronger than the Inland Taipan. They can grow to lengths of up to 1 m, have a slender body with a yellow case and green crossbands and are found among the tropical reefs of the Indian Ocean.

Luckily for humans, these dangerous snakes are also found to be of a shy and timid temperament.

7.5K views12:30
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2023-05-25 06:30:00
Does the deadliest snake in the world have the most potent venom?

The Saw-Scaled Viper
(Echis Carinatus) has the reputation of the world’s deadliest snake as it is believed to be responsible for more human fatalities than all other snakes put together.

They have a stout body with a pear-shaped head which is distinct from the neck. They can grow up to 0.9 m and come in shades of brown, grey, or orange with darker dorsal blotches and lateral spots.

They are nocturnal, feed on different small animals, move sideways (sidewinding locomotion) and can be found in arid regions north of the Equator across Africa, India, Sri Lanka, Pakistan, and the Middle East.

Their venom is far from being as potent as that of the most venomous land snakes. However, they are often found in populated areas where a lack of readily accessible antivenom in rural areas adds to their lethality. So, the potency of the venom has no bearing on the list of world’s deadliest snakes.

6.5K views03:30
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2023-05-24 12:53:12
What’s the difference between venom and poison?

The terms "venom" and "poison" are not interchangeable, the distinction is more about style than substance.

Venom is injected directly by an animal, whereas poison is delivered passively, such as by being touched or ingested.

Poison and venom don't always work the same way. Venom won't necessarily hurt someone unless it enters the bloodstream while some poisonous animals can cause immediate death if ingested.

Scientists proposed a third category of natural toxins: the "toxungens” that are actively sprayed or hurled toward their victim without an injection. For example, spitting cobras can spew toxins from their fangs.

If the distinctions between poisons, venoms and toxungens seem a little arbitrary, it's because they sort of are; in some languages, there is only one word for both "venom" and "poison." In Spanish, for example, both are translated as "veneno."

6.0K views09:53
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