Nikon DX Cameras

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D500 The flagship model within Nikon’s DX-format DSLR line $1,896.95
D7500    
     
     
     
   

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Nikon Full Frame Cameras

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D5
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$6499.95
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D850
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$3299.00
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D750
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1800.00
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D750
(refurbed at nikon.com)
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$1300.00

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D610
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$1500.00
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D810
(refurbed at nikon.com)
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$2200.00

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The Byzantine Empire (330–1453)

Back to History Of The Middle Ages


  1. Introduction
    1. Maps of the Balkan Peninsula
    2. Chronology of Byzantine Empire
    3. A Narrative on Byzantine Empire by H G Wells
    4. List of Rulers of Byzantium
  2. Early Byzantium Emperors 324 -867 AD
    1. Constantine the Great, of IllyrianGreek origin
    2. Theodosius I,  379-392 (last emperor to rule over the full extent of the empire)
    3. Age of  Justinian (527-65)
    4. Gothic war between Byzantine and Ostrogoths 535-40AD
  3. Middle Byzantium Emperors 867 – 1204 AD
    1. Sack of Constantinople in 1204: Fourth Crusade
  4. Nicaean Emperors 1204-1261
  5. Late Byzantium Emperors (The Palaiologoi) 1259 – 1453
  6. Fall of Constantinople in 1453
  7. Relationship with the Kiev Rus north of Black Sea
  8. Relationship with the Muslims

Nikon Lenses

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25mm

35mm

50mm

100mm

200mm

400mm

800mm

1200mm

Assessment of different focal lengths — wide angle to telephoto — by taking picture of same object from the same place with the same camera.


Review of the basics


Choosing a Focal Length

Another snapshot

Lenses-Focal-Lenghts-03

Focal Lengths

 


Nikon FX (Full Frame) Lens Comparison Table

LENS PRICE CATEGORY WEIGHT APERTURE VR FILTER DX EQUIV.
Nikon 24-70mm f/2.8E  $2,397 Travel/portrait 37.7 oz. f/2.8 Yes 82mm 36-105mm
Nikon 50mm f/1.4G $447 Travel/portrait 9.9 oz. f/1.8 No 58mm 75mm
Nikon 14-24mm f/2.8 $1,897 Wide angle 35.3 oz. f/2.8 No None 21-36mm
Sigma 35mm f/1.4 Art $799 Street/travel 23.5 oz. f/1.4 No 67mm 52.5mm
Nikon 70-200mm f/2.8E  $2,797 Telephoto 50.4 oz. f/2.8 Yes 77mm 105-300mm
Nikon 85mm f/1.8G $477 Portrait 12.4 oz. f/1.8 No 77mm 127.5mm
Nikon 28-300mm f/3.5-5.6G  $947 All-in-one 28.2 oz. f/3.5-5.6 Yes 77mm 42-450mm
Nikon 16-35mm f/4G $1,097 Wide angle 24 oz. f/4 Yes 77mm 24-52.5mm
Nikon 24-70mm f/2.8G $1,797 Travel/portrait 31.8 oz. f/2.8 No 77mm 36-105mm
Nikon 105mm f/2.8G Micro  $897 Macro 25.4 oz. f/2.8 No 62mm 157.5mm
Nikon 70-300mm f/4.5-5.6E  $747 Telephoto 24 oz. f/4.5-5.6 Yes 67mm 105-450mm
Tamron 15-30mm f/2.8 $1,199 Wide angle 38.9 oz. f/2.8 VC None 22.5-45mm
Nikon 35mm f/1.8G $527 Street/travel 10.8 oz. f/1.8 No 58mm 52.5mm
Nikon 200-500mm f/5.6E $1,397 Super telephoto 73.7 oz. f/5.6 Yes 95mm 300-750mm
Nikon 24-85mm f/3.5-4.5G $497 Travel/portrait 16.4 oz. f/3.5-4.5 Yes 72mm 36-127.5mm

Lens loyalties
Camera bodies come and go, but lenses are a long-term investment. The Nikon D50 you bought years ago may be obsolete but the lens that came is just as good today as it was then.


Interchangibility of lenses between Full Frame (FX) and APS-C (DX) formats

Nikon started off making DX-format DSLRs and a whole range of DX-format lenses to go with them. If you do decide to upgrade to the full frame FX format you’ll almost certainly have to invest heavily in new lenses too.

You can use DX-format lenses on FX-format Nikons, but only in ‘crop’ mode. The camera restricts the sensor area to a DX-sized rectangle in the middle, and you don’t get the benefit of the sensor’s full resolution.

For example, in crop mode, the 36-megapixel D800 produces images of 15.3 megapixels, while the 16-megapixel D600 drops to 6.8 megapixels. So, using your DX lenses is not a long-term solution.

Of course, you may have some FX lenses already, like Nikon’s 70-300mm f/4.5-5.6 telephoto zoom, which is a popular choice for DX-format SLR owners but is actually an FX-format zoom.

If you are considering moving to an FX camera in the future, start investing in FX-format lenses now because they’ll work on any DX-format Nikon DSLR in the meantime.

Electricity and Magnetism

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Milestones in Electricity

  1. From Greek period to 18th Century: transient or ephemeral electricity in the form of sparks and shocks
  2. Invention of steady electricity: The Volta Pile in 1800s
  3. Faraday and Maxwell
  4. 1881: First International Exposition of Electricity at Paris
  5. 1893 World’s Columbian Exposition in Chicago: AC Power Generator
  6. Invention of Transistors

 

Development of Electricity

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During prehistoric times, early humans were aware of lightning, sting rays, electric eels, and static charges in dryclimates

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600 BC: The Greek philosopher Aristophanes was aware of the peculiar property of amber, which is a yellowish translucent resin. When rubbed with a piece of fur, amber developed the ability to attract small pieces of materials such a feather. For centuries this strange inexplicable peopety was thought to be unique to amber.

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Thales (640-546 BC) rubbed amber (elektron in Greek) with cat fur and picked up bits of feather.

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341 BC: Aristotle wrote about a fish called torpedo which gave electrical shocks and paralyzed muscles if touched.

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250 BC: A Galvanic cell composed of copper nd iron immersed in wine or vinegar called the Baghdad Batter was excavated in Baghdad by Wilheim Konig in 1938 and was dated back to 250 BC.

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1600 AD:

Gilbert also studied magnetism and in 1600 wrote “De magnete” which gave the first rational explanation to the mysterious ability of the compass needle to point north-south: the Earth itself was magnetic. “De Magnete” opened the era of modern physics and astronomy and started a century marked by the great achievements of Galileo, Kepler, Newton and others.

Gilbert recorded three ways to magnetize a steel needle: by touch with a loadstone; by cold drawing in a North-South direction; and by exposure for a long time to the Earth’s magnetic field while in a North-South orientation.

1600 AD: Sir William Gilbert (1544-1603), the Court Physician to Queen Elizabeth I, proved that many other substances besides amber displayed electrical properties and that have two electrical effects. When rubbed with fur, amber acquired resinous (negative) electricity; glass however, when rubbed with silk, acquired vitreous (positive) electricity. Electricity of same kind repels and of opposite kind attracts. Gilbert’s book On the Magnet and Magnetic bodies and on the great magnet the Earth published in 1600.
They did not realize that an equal amount of opposite electricity remained on the fur or silk. Dr. William Gilbert, realized that a force was created, when a piece of amber (resin) was rubbed with wool and attracted light objects. In describing this property today, we say that the amber is “electrified” or possesses and “electric charge”. These terms are derived from the Greek word “electron” meaning amber and from this, the term “electricity” was developed. It was not until the end of the 19th century that this “something” was found to consist of negative electricity, known today as electrons.

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1646: Walter Charlton coined the term electricity.

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1663: Otto von Guericke first published the phenomenon of static electricity snd built a machine to produce it. Also Read: The History of Electrical Machines

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1729 – Conductors and Nonconductors

Stephen Gray was the first to systematically experiment with electrical conduction. Until his work in 1729 the emphasis had been on the simple generation of static charges and investigations of the static phenomena (electric shocks, plasma glows, etc.). He also first made the distinction between conduction and insulation, and discovered the action-at-a-distance phenomenon of electrostatic induction.
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 1747: Ben Franklin during a thunderstoem demonstrated that lightning was an electrical discharge. The experiment was extremely hazardous, but the results were unmistakable: when he held his knuckles near the key, he could draw sparks from it. The next two who tried this extremely dangerous experiment were killed.
Watson passed an electrical charge along a two-miles long wire.

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Resolutions of the International Congress of Electricians, Paris, 1881

(1) That the cgs system of electromagnetic units be adopted as the fundamental units.

(2) That the practical units, the ohm and the volt, preserve their previous definitions, 109 and 108 cgs units respectively.

(3) That the unit of resistance, the ohm, be represented by a column of mercury 1 mm² in cross-section at the temperature of 0° C.

(4) That an international commission be charged with the determination, by new experiments, of the length of the mercury column 1 mm² in cross-section at a temperature of 0° C.

(5) That the current produced by a volt in the ohm be called an ampere.

(6) That the quantity of electricity produced by a current of 1 ampere in one second be called a coulomb.

(7) That the unit of capacity be called a farad, which is defined by the condition that a coulomb in a farad raises the potential 1 volt.


The term electroscope is given to instruments which serve two primary purposes: 1) to determine if a body is electrified, and 2) to determine the nature of the electrification. An electrometer, on the other hand, is a specialized form of electroscope that includes a calibrated scale for reading the strength of the charge.

Electricity:

  1. Progress before the invention of Volataic Battery
  2. Invention of the Voltaic Battery
  3. Post Voltaic Battery

  1. Otto Guericke Ref 1, Ref 2, Ref 3
  2. Next

Heinrich Hertz

Back to Master Index of Science


Heinrich Hertz’s Wireless Experiment (1887)

Spark-Gap Transmitter


Hertz-Experimental-Setup-00

Hertz’s Experimental setup schematic diagram

Hertz-Experimental-Setup-05

Hertz-Experimental-Setup-03

Hertz Experimental Setup

Electro-Magnetic-Wave-00

EM Wave from Hertz’s experimental setup


Electro-Magnetic-Wave-01_In_3D.gif

The EM wave in 3D Animation

Electro-Magnetic-Wave-08

 


Hertz Experiment

Hertz-Experimental-Setup-00

Hertz-Experimental-Setup-03

The existence of electromagnetic waves was confirmed experimentally by Hertz in 1888. This experiment is based on the fact that an oscillating electric charge radiates electromagnetic waves. The energy of these waves is due to the kinetic energy of the oscillating charge.

Due to high potential difference across S1 and S2, the air in the small gap between the spheres gets ionized and provides a path for the discharge of the plates. A spark is produced between S1 and S2 and electromagnetic waves of high frequency are radiated. Hertz was able to produce electromagnetic waves of frequency about 5 × 107 Hz.

Here the plates A and B act as a capacitor having small capacitance value C and the connecting wires provide low inductance L. The high frequency oscillation of charges between the plates is given by

Hertz-Experimental-Setup-04


EM-Wave-Spectrum-05

Our eyes are designed to detect a small portion of the electromagnetic spectrum. This part of the spectrum is called the visible light region. The visible light region ranges in wavelengths from about 380 or 400 nm to 700 or 780 nm.  In terms of frequency, this corresponds to a band in the vicinity of 430–770 THz.

Light waves travel at very high speeds and are absorbed or reflected by various objects. If all the waves are absorbed and none reach our eye then we do not see anything and the image before us appears as having the color of black. If the object reflects all wavelengths of light equally then the object appears to be the color of white. If an object on the other hand reflects light of certain wavelengths but absorbs others then the color of the object will match the wavelengths that are reflected.


EM-Wave-Spectrum-01

Table 5.1 shows various regions of electromagnetic spectrum with source, wavelength and frequency ranges of different electromagnetic waves.

Spectrum_of_waves_06_With-Energy

Spectrum of waves

spectrum_of_waves_05


Other areas of 19th century physics were challenged by discovery after discovery tied to improvements in technique and materials. Hitherto unknown types of radiation were detected, not directly by the human senses, but by their physical effects. Thus 1799 brought the discovery of infrared rays; 1800, ultraviolet rays; 1886, radio waves; 1895, x-rays. The apparent stability of matter itself was shattered with the discovery of radioactivity by Henri Becquerel in 1896.

The high point of this scientific turmoil was the discovery of two new types of universal forces: electricity and magnetism. Alessandro Volta’s pile, the first battery, was assembled in 1800. Flowing electricity was found to create magnetism by Hans Ørsted in 1820. Michael Faraday showed that changing magnetic fields created electricity in 1831, and thus created the basis for modern electrical power generation. Faraday also first described magnetism using the concept of a field of magnetic lines existing in definite physical relations with other forms of matter. Contemporaries viewed this field as merely a mathematical abstraction, but the later work of Maxwell and much of 20th century physics showed that fields do in fact exist as an independent material reality.

The full theory of these phenomena was worked out by James Clerk Maxwell, whose equations of 1861 and their refinement in 1865 would unify electricity and magnetism into a new theory of electromagnetism. This theoretical unity for a natural force was matched only by Newton’s work on gravitation, two centuries previously. The great physicist Ludwig Boltzmann gave some voice to the impact Maxwell’s contribution made when he quoted Goethe’s Faust: “Who was the god who wrote these lines?”

Maxwell’s equations, tested by Heinrich Hertz’s deliberate construction of equipment to produce and detect the predicted waves we now call radio, suggested the various other “rays” already discovered composed a common form as electromagnetic waves. What distinguished them was simply the wavelength between crests in an electromagnetic spectrum of radiation.

Into this ferment was born Albert Einstein in 1879, just months before Maxwell’s death. The young Einstein was captivated by Maxwell’s work. In autobiographical notes, he stated, “The most fascinating subject at the time I was a student was Maxwell’s theory.” Inspired by Maxwell’s study of light, a 16-year-old Einstein conducted his first significant gedankenexperiment (thought experiment). He imagined what it would be like to ride along such an electromagnetic wave at the same speed. Would it appear frozen, since the motion would be along its crest, like surfing along an ocean wave? The equations did not admit this possibility. More intriguingly, the theory of electromagnetism posited a fixed velocity—the speed of light—while Newton’s equations implied no such limit, instead describing the force of gravity operating with instantaneous effect.


References

  1. https://www.wsws.org/en/articles/2015/12/07/ein1-d07.html
  2. Hertz and Radio Waves Explained by High School Physics Explained
  3. PHYS 101/102 #1: Electromagnetic Waves by Cornell University — Youtube Video

Newtonian Gravity Vs General Relativity

Back to Issac Newton


General relativity & Gravity by stevebd1 Youtube


Warping of space around the sun

GETTING A GRIP ON GRAVITY  Einstein’s general theory of relativity explains gravity as a distortion of space (or more precisely, spacetime) caused by the presence of matter or energy. A massive object generates a gravitational field by warping the geometry of the surrounding spacetime.


If a light ray happens to pass close to a massive object such as a star, it will be forced to bend in order to follow the curved space around it.

Notice that in the above figure, the star at position at location “Real” can only be seen at position “Observed” from the earth if the light bends as shown. If the light did not bend, you would not see the star because it will be blocked by the sun shown in the middle.

The picture above shows how the direction of light will be affected by the  curved space around the sun. Light emanating from the “Real” position will curve around the outermost fringe of the curved space around the sun, and then, once out of the curved space, will travel in a straight line to the earth. From the earth, it will appear like the star is at the “observed” position when, it actually is at the “Real” position.

bending-of-light-03

bending-of-light-02

Newton first computed the angle of the bending light as 0.87 arc second, Einstein in 1915 modified it to be the double of that which is 1.75 arc second. From the angle of bend, the physicists computed the weight of light.

When the sun is not anywhere close to the path between the earth and the star, you could see the star at the “Real” position because the light will travel in a straight line to the earth.


Gravitational Lensing

Gravitational_lens-full

Gravitational lensing was first observed in 1979, but Einstein had suspected its possibility in 1912, even before his theory had been completed.

The bending of light by gravity can lead to the phenomenon of gravitational lensing, in which multiple images of the same distant astronomical object are visible in the sky.

This diagram shows how light from a distant galaxy bends around a massive object in the foreground, perhaps a neutron star or a black hole. The orange arrows show the apparent position of the background galaxy. A duplicate or multiple image can be observed from Earth. The white arrows show the path of light from the true position of the source.


Angle of the bending light

Einstein  in 1911 obtained a deflection angle of (radians) = 0.87 arc second,  which is the Newtonian value.

About four years after his first paper in 1911, Einstein had developed the General Theory of Relativity (1915) which prompted him to modify the above Newtonian value by adding the effect of curved space thus doubling the bending angle resulting in a new value of 1.75 arc seconds (1.7505395 arc second). The new result was published by Einstein on November 18, (1915) and was experimentally verified by Crommelin and Eddington during the solar eclipse expeditions of May 29, 1919.


Any large mass distorts the geometry of space around it (Note the word “around”), for instance making parallel light rays diverge or converge. One consequence, described by Einstein’s general theory of relativity is that objects behind a body such as the Sun may look magnified or distorted as the optical path of light goes through the region of warped space.

The bending of light in gravitational fields is much better explained by Snell’s law of refraction (see Fig. 1) which was experimentally established by Willebrod Snell and theoretically by René Descartes over three hundred years ago.


Bending Light
The first prediction put to test was the apparent bending of light as it passes near a massive body. This effect was conclusively observed during the solar eclipse of 1919, when the Sun was silhouetted against the Hyades star cluster, for which the positi ons were well known.

Sir Arthur Eddington stationed himself on an island off the western coast of Africa and sent another group of British scientists to Brazil. Their measurements of several of the stars in the cluster showed that the light from these stars was indeed bent as it grazed the Sun, by the exact amount of Einstein’s predictions. Einstein became a celebrity overnight when the results were announced.

The apparent displacement of light results from the warping of space in the vicinity of the massive object through which light travels. The light never changes course, but merely follows the curvature of space. Astronomers now refer to this displacement o f light as gravitational lensing.


Important Historical Anecdote: The solar eclipse of 1919 

Albert Einstein’s prediction of the bending of light by the gravity of the Sun, one of the components of his general theory of relativity, can be tested during a solar eclipse, when stars with apparent position near the sun become visible.

Two expeditions were made to measure positions of stars during this eclipse. The first was led by Sir Frank Watson Dyson and Sir Arthur Eddington to the island of Principe (off the west coast of Africa), the second by Andrew Claude de la Cherois Crommelin and Charles Davidson to Sobral in Brazil.

The expedition to observe the eclipse proved to be one of those infrequent, but recurring, moments when astronomical observations have overthrown the foundations of physics. In this case it helped replace Newton’s Law of Gravity with Einstein’s theory of General Relativity as the generally accepted fundamental theory of gravity.

Following were the three possibilities: There might be no deflection at all; that is to say, light might not be subject to gravitation. There might be a `half-deflection’, signifying that light was subject to gravitation, as Newton had suggested, and obeyed the simple Newtonian law. Or there might be a `full deflection’, confirming Einstein’s instead of Newton’s law.


The nice thing about using mass instead of mass is that mass is a property that all observers agree on, whereas mass is not. There aren’t that many properties of an object that are like this.  Take the speed of an object; different observers won’t agree on what it is.  For instance, there goes a car; how fast is it moving? Well, from your point of view, standing by the road, perhaps it is moving at 80 kilometers per hour.  But from the point of view of the car’s driver, the car isn’t moving at all; you’removing.  And from the point of view of someone in a car going the other direction, the first car may be moving at, say, 150 kilometers per hour.  The bottom line?  Speed is a relative quantity; you cannot ask, what is the speed of the car, because it has no answer.  Instead you must ask, what is the object’s speed relative to a particular observer.  Every observer has an equal right to make the measurement, but different observers will get different answers.  Galileo’s principle of relativity (long before Einstein’s principle of relativity, which involved adjusting Galileo’s principle)  already incorporated this idea.

This dependence on the observer also applies to energy, and to momentum.  And it applies to relativistic mass.  That’s because relativistic mass is simply the same as energy, divided by a constant — namely, c² — and so, if you define mass to be “relativistic mass“, then different observers disagree about an object’s mass m, though all agree that E=mc².

But rest mass, or, as I would call it, “mass“, does not depend on the observer, which is why it is also called invariant mass.  All observers agree on an object’s mass m, with this definition.  And all observers agree that if you were stationary with respect to the object, you would measure its energy to be mc², and otherwise you would measure its energy to be larger.[3]


Newton’s equations still differed from Maxwell’s equations in that they implied instantaneous action, that is, infinite velocities. Special relativity had decisively shown that the fastest velocity was that of light, thus limited the speed at which even gravity could influence matter.


E equals m cee squared

One of the consequences of Einstein’s theory is that mass and energy, rather than subject to separate and independent conservation laws, are conserved together and are therefore at some fundamental level equivalent. This famous equivalence of mass and energy is expressed in the equation known across the world: E=mc2. The speed of light links small amounts of mass to enormous amounts of potential energy. Originally thought to be only of academic interest, this conversion was later carried out through the mechanism of the nuclear fission chain reaction. The energy released by the two atomic bombs dropped by the United States at the end of World War II, which each incinerated a city, was the equivalent of less than one gram of mass.


 

References

  1. http://archive.ncsa.illinois.edu/Cyberia/NumRel/GenRelativity.html
  2. https://www.forbes.com/sites/startswithabang/2017/08/04/americas-previous-coast-to-coast-eclipse-almost-proved-einstein-right/#214629e737c3
  3. https://profmattstrassler.com/articles-and-posts/particle-physics-basics/mass-energy-matter-etc/more-on-mass/the-two-definitions-of-mass-and-why-i-use-only-one/
  4. http://ircamera.as.arizona.edu/Astr2016/lectures/physicallaws.htm
  5. https://www.sciencenews.org/article/einsteins-genius-changed-sciences-perception-gravity
  6. https://www.wsws.org/en/articles/2015/12/07/ein1-d07.html