Archive for the ‘Science’ Category

Why 28 mm is the best focal length for travel photography?


If you have no other focal lengths available or have to choose one only

Note: 28 mm is for Full Frame camera. For APSC sensors it is 19 mm and for Micro Four Third [MFT] sensor it is 14 mm.

First let us define what is meant by travel photography. This include different styles of photography like [but not limited to]:

⦁ Landscape [in clear day light, cloudy/overcast, rain etc.]
⦁ Street / city life
⦁ Indoor [museum, underground etc.]
⦁ Fast action [when shooting from moving vehicle/train etc.]
⦁ Night life at city
⦁ Environmental Portrait

Before going into debate of which focal length is best, let us first examine how human eyes see. Scientists say that human eyes’ focal length varies from 35 mm to 50 mm [in full frame camera terms]. Unlike a camera, human eyes see clearly things at the center of our vision and objects in our peripheral vision is blurred. It is important to understand we are talking of what our brain interprets of what our eyes see. To test this, raise your hand so that it is parallel to you ear and then wave your hand. Your eyes can detect the hand movement in your peripheral vision but you can’t see it clearly. This is also why we often can’t find things in our homes unless it falls into our hands or just in front of us.

Online camera forum users often discard lenses because those are not sharp at corners, yet in real life, when humans see photos, people hardly examine sharpness at the corners.

Anyway, coming back to the travel photography. You may think that 50 mm would be ideal for lens. But no – while 50 mm is considered good focal length for portraits, it is too narrow for general travel photography.

In travel photos, we want to capture the surroundings as much as possible. So we need a wide field of vision – but not necessarily an ultra wide angle lens because an ultra wide angle lenses distort perspective, especially at the periphery.

So we need a focal length which is wide enough yet does not distort things – especially human faces because people shoot lots of family photos in holidays.

Most mobile phone cameras have 27-28 mm [full frame equivalent] focal length for their primary cameras. However, you may have noticed, if you shoot selfie while holding phone too near to your face, your face looks bit distorted compared to if someone takes the photo of you holding camera bit far away from you.

Mobile phone manufacturers did lot of research to find out which focal length would keep most consumers happy. Many people now buys smartphones for shooting photos as primary purpose, other than sending messages in chat apps. So having offering a good camera is utmost important for mobile phone manufacturers.

Thus, for most travel shots we want to fit more things in our photos. 28 mm is a focal length which can fit things without distorting them. Go over 28 and it becomes difficult to fit things especially in places where you can’t move backward due to physical barriers or obstacles. Go below 28 and it starts to become too wide angle and thus things start to become distorted at the corners.

There are other advantages of this slightly wide angle focal lengths. Not all consumer cameras have in body image stabilizer or lens stabilizers. In day time, it is comparatively easier to keep hands steady with a short shutter speed, which results in sharp photos. Higher the focal length, more difficult it is to keep hands steady without shaking. Typical thumb rule is that if focal length of lens is f mm, then shutter speed must be less than 1/(f * crop factor). So for a MFT camera with 14 mm lens, the slowest shutter speed you can go is 1/(2*14) or 1/28 or typically 1/25 s to 1/30 s. This is good for night shots because usually in bright day light photos you keep shutter speed 1/125 s to 1/250 s depending on light intensity.

Of course there are special circumstances where you do need telephoto lenses like when you cannot physically reach nearer to your subject – like birds, wild life/safari etc.

However, many cameras offer some kind of built-in zoom features. This could be either digital zoom or tele-converter. With digital zoom, the camera computationally interpolates values so there is a chance of slight fall in image quality. Some proper cameras offer extended tele-converter feature, where effectively you get an in camera crop which does not reduce image quality – though it may reduce the resolution by a little bit due to cropping.

Sometimes you may find even 28 mm is not wide enough to capture the vista of a landscape. Usually you can use panorama feature in your phone or camera. If no such feature available in your camera, you can still achieve it albeit with few steps. Use [AE-L] or Auto Exposure Lock facility in your camera. Turn it on and make you exposure remains the same while you take few shots by panning your camera. Then on your computer you can stitch those photos to produce a stunning panorama.

If you shoot with a zoom lens in your camera then having an ideal focal length is less of an issue. Though, depending on camera and lens set up, such combination can be quite big and heavy to carry on. Hence, a small camera with a prime lens (which has single focal length) reduces the burden of camera gears to a great extent.

If you travel with interchangeable lens camera [ILC] then 28 mm [or equivalent] prime lenses often have large apertures, allowing you to capture enough light for night/low light photos. Tpically kit zoom lenses don’t have such large apertures [barring few pro lenses, which are usually heavy and expensive].

If you want to buy a prime lens for your camera and confused which focal length to use, hopefully this article will help you decide that.

Majority of single focal length cameras use focal lengths around this value. For example,

⦁ Fuji X100 series camera uses 23 mm lens [35 mm FF eqv.]
⦁ Fuji X70 camera with 19 mm lens [28 mm FF eqv.]
⦁ Rico GR III camera uses 18 mm lens [27 mm FF eqv.]
⦁ Leica M2 camera uses 28 mm lens [FF]
⦁ Sony RX1R camera uses 35 mm lens [FF]

Abbreviations used
FF = Full Frame camera
APSC = APS-C sensor camera
MFT = Micro Four Third camera
FL = Focal Length

Covid19 – potential exit strategy

Please note that things are changing very fast on Corona virus. Scientists are working hard to find a vaccine. Hence, the content of this blog could become out of date very soon. This blog is for information purpose only and does not constitute as medical advise. Always follow the advise from your doctor and relevant medical authority in your country.
How can lock down be lifted?
The key question for most part of the world is now how to end the lock down without a massive risk of life of citizens.

As of this writing, there is no known cure for Covid19.

If nothing is done, entire population will eventually catch the virus and around 1% of them will die.

If we could confirm who are immune to the virus then we can easily identify the vulnerable and ask everyone else to carry on with life as usual. However, the problem is, other than identifying aged people (e.g. those with 65 years and above) and those with existing health conditions (e.g. obesity, cardiac issues, diabetes etc.) there is no finer way to identify the risk group. Even them, some young and healthy people are randomly affected in a serious manner, even resulting to death!

Millions of people around the world have got infected with Covid19. Some have suffered no or mild symptoms only. However, due to very little testing carried out, majority of people who think they have got Covid19 and recovered, have no way to confirm that that is actually the case!

The crux of the problem here is how to identify people who got Covid19, then recovered and thus assumed immune to it. These people can then come out of lock down and start leading a pre-Covid19 life.

So how do you confirm this? This is where the difficulty lies.

Presence of the virus can be confirmed in 2 ways – swab test and antibody test.

The swab test shows if the virus is present at the point in time (when patient is tested).

WhatsApp Image 2020-04-24 at 12.08.57
The antibody test can detect patients who suffered and recovered but up to a certain period of time. The big unknowns are [1] how long antibody will remain in the body [2] whether the antibody is due to Covid19 only or for some other viruses.

Although there are cases for person being affected again after recovery, but in this writing we are assuming subsequent infection would not be fatal .

Now if we take a person A, who got infected by Covid19 but suffered only mild symptoms and recovered after 21 days, then the question remains how to prove it? He can be tested for antibody and if IgG antibody is found, a reasonable conclusion can be drawn that person A is immune from Covid19 going forward.

But this approach has a major hurdle. Firstly, antibody test is not yet available to everyone. Secondly, by the time antibody test is available to everyone, the concerned person may have lost the antibody from his blood stream. In this case, it is back to square one!

WhatsApp Image 2020-04-24 at 12.12.16
This person is now in same position like one who has never caught Covid19 before (say person B).

To the public, person A is having same risk of person B. But in reality person A is possibly immune and carry far less risk than person B. But there is no way to prove it.

For person B, there is a risk that he could suffer mild symptom or sever symptom and could even die.

If the immunity can be proved beyond doubt, then it is a valid exit strategy.

Without proper tests, we have to adopt any of following situations.

[1] Lives saved but economy damaged

Continue lock down indefinitely. If everyone remains isolated, no one will get infected, hence no one is contagious and no new person gets infected. But this will destroy the economy and livelihood of billions of people. This is not acceptable solution to public – even though this is actually best solution for saving maximum amount of lives. After sometime public may revolt and might just start their normal life anyway.

[2] Economy survives but high number of casualties

Allow people to carry on as usual and achieve so called herd immunity. This means allowing everyone to catch the virus and accept 1% death of overall population. Effectively a situation a very large number of random people will die. This scenario does not try to prevent infection, rather relies entirely on individual’s body immunity to tackle the virus.

What is the future then? Well, only time will tell.

Thanks to Dr Somnath Mukherjee and Dr Shyam Das for their inputs.

Why the Great Pyramids are still standing?


The Great Pyramids at Giza, Egypt are 5000 years old. It is astounding that such old structures are still standing. This is why they are considered among the most notable ancient wonders of the world.

A common question asked by public is that how come such old structure is still standing today yet some modern structures have fallen apart.

Let us understand the engineering principle and philosophy behind these legendary structures.

The pyramids were built as tombs – the resting place of mighty pharaohs!

These pyramids are built of lime stones and granite. Effectively these are huge rocks weighing 2500 kg each on average.

From the engineering point of view, the pyramids are built using compression elements only. A modern concrete building consists of columns, beams and slabs. The columns only carry compression force. However, the beams and slabs carry both compression and tension forces.

If you take a beam, for example, which is subjected to a load on its top, the areas above the center line will experience compression where as the area below the center line will experience tension. Concrete is weak in tension so reinforced steel bars must be placed inside concrete the carry then tension force. Any bending force on any structural member will introduce both compression and tension forces.

Rocks cannot carry tension forces. They will be break if they are designed to carry tension. But, they are extremely good at carrying compression forces! The blocks in pyramids were designed to carry compression forces only. They do not experience any kind of bending force, hence no resultant tensile stress because of this.

Also, as pyramids housed the deads only (excuse the pun), there are no moving mechanisms inside them. A modern house has lots of moving parts like doors, windows (opening/closing), water flowing thru pipes etc. The act of people living inside houses causes some wear and tear.

The pyramids experienced no such wear and tear arising from its inhabitants – because they were dead anyway. However, we need to keep in mind that pyramids experienced great forces of nature in the form of erosion and vandalism by humans over thousands of years.

The other important aspect contributing their longevity is the arid weather in the desert. The lack of moisture in the atmosphere meant there were no water trapped between joints in the structure. The blocks were placed so that they kind of attached to each other like Lego. They did use some mortars though. In other parts of the world, some water would have invariably trapped inside those mortars and would have expanded causing cracks. But in arid weather, there was no such thing of water expansion – because there were no water in the first place.

So to phrase it differently, if the pyramids were built in tropical area, say inside Amazon rain forest, it would have been experienced a different kind of destructive forces like water ingress and roots from trees. In fact, this is how a more modern (comparatively) Ankor Wat temple complex got deteriorated over shorter span of time.

In spite of all these, there is no equivalent yet for the Great Pyramids.

Why film cameras are making a comeback?

Film cameras at the moment covers only a niche corner in photography market. However, in recent years, their popularity has gone up for the first time after the mass consumption of digital photography.
The major disadvantages of film photography are:
  1. Not being able to view the photo immediately after shooting. So no corrective action is possible while being on the spot.
  2. Film speed (ISO) is fixed for the whole of shooting. In digital cameras, it is possible to change ISO for every photo depending on lighting condition.
  3. Limited photos that can be shot from each roll of film.
However, there are advantages of film photography:
  1. Due to limited photos available in each film, you will be forced to think about composition as not to waste film. This can, subjective though, can turn into a better photographer.
  2. 35-mm film cameras are cheaper than full frame digital cameras.
  3. 35-mm film cameras are often smaller than full frame (or even APS-C) digital cameras. This is because image processing happens outside film camera (during negative development) whereas in a digital camera, manufacturers need to put an image processing mechanism inside the camera. This makes digital cameras larger than film cameras.
  4. Flim photos last longer. Printed album is less susceptible to file corruption than digital forms.
  5. People are more likely to browse their printed photos compared to digital photos.
  6. Some people find hands-on film development more rewarding as hobby.
  7. Film cameras have nostalgic values to some people and they feel proud of that. Some shooters also feel film cameras can differentiate them from the digital camera mass crowd.
  8. Mechanical film cameras can operate without batteries.
  9. Longevity – digital cameras have typical life of 10 years whereas mechanical film camera can lasts over 50 years.

Happy shooting.

Difference between Indian and Western music notation


New musicians, especially who studied Indian swaralipi first and trying to study Western staff notation (and vice versa), often get very confused about how to align Indian swaralipi with western staff notation.

The key thing to understand here that in Western Music notation, each symbol represents an absolute note. For example, in a staff notation you always see whether it is C4 or C5.

However, in Indian swaralipi (= sa re ga ma pa dha ni) is made of relative notes!

The Sa can be C, D, E, F, G, A, B anything! In fact it can be C# or Ab too.

When you play a western staff music notation, you are expected to play exactly as it is written. That means, staff notation shows whether you will have to play C4 or G#3 etc.

However, when you play a Indian swaralipi, since only relative notes are shown, it is up to the player to choose which scale s/he wants to play in!

For example, here is Indian swarlipi notation for national anthem Jana Gana Mana (first line)

Sa Re Ga Ga | Ga – Ga Ga | Re Ga Ma – |

Now it is the player’s discretion whether s/he wants to start Sa in C or D or E or whatever.

Suppose, you have staff notation for this tune in C major. If you follow that notation, you have to play in C major. However, one can still play it in other scale like D major, F major etc. – by transposing it to a target scale (software like MuseScore can do it by flick of a menu).

In a way, the Indian notation is easier since it is entirely relative and you are free to play at any scale of your choice. Western staff notation is more rigid in this aspect (though you can re-write it by transposing – as mentioned earlier). However, staff notation is very rich and can convey timings, rhythm, chords etc. in much more details compared to swaralipi.

Any Indian tune or swaralipi can be always converted (manually) to staff notation. The reverse is also true, though you are likely to loose some complex information as there is no swaralipi equivalent of some concepts of staff notation.

There is a dearth of good quality written Indian tunes (compared to western music whether you can get notation of almost any popular tune). This is because Indian musicians predominantly play by ear where as western counterparts play by ear and/or sight as well.

If you are an Indian musician but unable to read staff notation, I strongly recommend that you learn it. It is not only versatile (in spite of steep initial learning curve) but universal too. People from anywhere can exchange music using this format.

Free software like MuseScore, make it very easy to compose music using staff notation.

PS: full scale example

Indian swaralipi and Equivalent Western notes (in C major)

Sa – C (C4 if mapping it with piano’s middle C key)
komal re – C# or Db
Re – D
komal ga – D# or Eb
Ga – E
Ma – F
kori ma – F# or Gb
Pa – G
komal dha – G# or Ab
Dha – A
komal ni – A# or Bb
Ni – B
Sa (next octave) – C

Indian swaralipi and Equivalent Western note (in D major)

Sa – D
komal re – D# or Eb
Re – E
komal ga – F
Ga – F#
Ma – G
kori ma – G# or Ab
Pa – A
komal dha – A# or Bb
Dha – B
komal ni – C
Ni – C# or Db


What are different types of watches?


Watches are broadly of 2 types – mechanical or quartz.

watch types

The easiest way to identify a quartz or mechanical watch is to look at the movement of second hand. Quartz watch will have second hand which jumps every second where as in a mechanical watch, the second hand moves continuously.

Mechanical watches don’t have batteries so they need regular winding to make them work. Obviously, in modern world such action is bit awkward. So there is a different watch type, called automatic. They are also mechanical watches but they are powered by normal hand movement as part of your standard day to day life.

AccuracyExtremely accurateCan gain/lose few seconds every day.

Feature Quartz Mechanical
Identification Second hand jumps or digital display. Second hand moves continuously and analog display.
Popularity 85-90% of all watches in the world are quartz. Only 10-15% of world’s watches are mechanical.
Power source Battery (some are rechargeable via light) Stores energy in springs via manual winding or normal hand movement (automatic).
Maintenance Don’t require any maintenance (other than battery replacement if necessary) Besides winding, these watches require servicing in every few years.
Like for like cost Cheaper Expensive
FeaturesAlso called “complications” in watch industry terms Can offer lots of features like multiple times, alarm, stopwatch etc. They can offer similar features too but such watches tend to be too expensive.
Manufacturing Automated via tools Some manual craftsmanship is often required.
Longevity Can last 10-20 years. With proper servicing, can last 50-100 years.
Accuracy Very accurate Can gain/lose few seconds every day.


The world of watches is very fascinating. Read about it on the internet in your spare time.

How a steam loco differs from diesel-electric loco?


A diesel-electric (DE) loco is a constant power machine. We know that, Power = Force x Velocity. This means, when hauling heavy loads (especially on an uphill), a DE loco can increase draw bar pull by reducing speed. This also shows why most shunting locos are DE locos as they need to haul heavy load but at low speed.


However, due to the way a steam loco is designed (i.e. its boiler, piston and other mechanisms), a steam loco behaves as a constant force machine up to cruising speed (usually around 25 MPH or 40 km/h). Beyond that, a steam loco behaves like a constant power machine like a DE loco.


This difference is crucial. For a steam loco to haul heavy load (or on an uphill), if it can’t deliver enough draw bar pull, it has no way to increase the force like a DE loco, because for steam loco, force is constant at low speed. So, a steam loco won’t be able to climb a slope like a DE loco. It will literally run out of puff under such circumstance. However, once a steam loco has crossed its cruising speed, it will have no problem pulling heavy trains as it behaves in same way as DE loco i.e. constant power loco.


There are obviously other differences between these two types of locos. A DE loco is more thermally efficient than a steam loco. The later requires far more maintenance than the former and needs more crews to operate them.


No wonder, due to these reasons, most of old steam locos have been replaced by DE locos in all but heritage routes. Please note that a pure electric loco will also behave similarly as of a DE loco.


What is heart attack?


The blood circulation in our bodies provides nutrition and oxygen to all cells. The muscles in heart are responsible for contraction and expansion of the heart. When enough oxygen do not reach to heart muscles, the heart cannot function properly. This usually happens when there are blocks or restriction to blood vessels, which carries blood to heart muscles. If heart cannot function properly it cannot push blood to other parts of the body, which in turn causes other body parts to malfunction. For this reason if heart attack is not treated immediately it can cause death.

There are several reasons why blockage occurs in blood vessels to heart. It can be due to age, lifestyle (like eating fatty food and not having enough exercise), genetic issue or other medical problems.

During heart attack, patients usually feel pain in chest and subsequently in many other body parts.

Heart attack is different from “stroke”. In heart attack, there is reduced blood flow to heart. In stroke, there is reduced blood flow to brain. Since brain controls functions of body, stroke is often associated with paralysis as a consequence. Since brain is divided broadly between left and right sections, stroke in one part of brain can often impair functionality of other side of the body (i.e. paralysis).

Both heart attack and stroke should be treated immediately as any delay can be fatal.


Air-cooled vs water cooled engine


Most likely your modern car has a water-cooled engine. When an internal combustion engine operates, it creates high amount of heat. Unless there is a mechanism to dissipate the heat, it will damage the engine components. In modern automobile engines, a coolant system is used to keep the engine cool. Usually a chemical coolant is used (although named water cooled, water is not used anymore now as coolant) within a sealed system (you rarely need to top up). The cooling system creates a jacket outside the engine. It also keep the engine in constant temperature. The proof is your car’s temperature gauge which usually stays halfway to H and C mark.

In air-cooled engine, air is used to cool the engine down. Thus, it does not require radiator and cooling system – which makes the whole engine a lot simpler. It uses radiator fins (easy to see in motorcycles) which are used to cool the engine. But there are drawbacks too. Unless there is steady flow of air, the engine may get overheat quickly. They are also very noisy as the radiators fins vibrate when engine is in operation.

Air-cooled engines are used mainly in motorcycles, some 3-wheels (like India’s Bajaj autorickshaws), some cars (classic VW Beetle, old Porsches etc.) and some propeller aircrafts.

For aircrafts, they are not a big problem. Unlike a car, an aircraft does not get stuck in traffic jams. Aircraft engines operate within their 80-100% RPM range most of the time and due to high speed cruising plenty of air pass over the radiator fins to keep them cool. This also explains why old propeller aircrafts with such engine sound so loud.

But problem might happen in air-cooled car engines! If the car is stuck in traffic or moving slowly over extended period of time, the engine may overheat (which may lead to seizure of engine).  On the other hand, they are quite good at cold weather condition as chance of overheating is lower.


Why auto stop start is modern cars?


Many new cars of today feature auto stop start feature. This is also known as Intelligent Stop and Go and similar names.

Cars with this feature, turns of engine as soon as you stop and take your foot off the clutch. Then as soon as you press clutch again to engage the gear, it switches on the engine.

Manufacturers do this because they claim it saves fuel while waiting in traffic.  This also allows them to quote higher fuel economy figures and CO2 emission (on which most cars are taxed nowadays). This makes these cars statistically more attractive (because of lower fuel consumption and tax) to the buyers.

On the other hand, many drivers find it as a psychological challenge. It also requires a stronger (thus more expensive) battery and starter motor. So how much money is saved at the end (for drivers) is open to debate.

Fortunately, if you do not like this feature, it can usually be turned off via a switch on dashboard.

As of now, automatic cars do not have this feature but in future this may be offered in autos as well.