Ask A Scientist

Have a question for our scientists? Send us your questions about optics and photonics!
L S of USA asks...

Why does the human eyeball see the image upside down and turned it around.

In the case of the eye, the image formed in the retina upside down "travels" through the optic nerve to the parts of the brain where visual information is processed and where perception occurs. This, according to the experience of the reality that the other senses have given us since birth, shows us the image already perceived as right. That is, we do not see with the eyes but with the brain. Proof of this is an experiment in which subjects were placed some special glasses that inverted the images, after a certain time of taking them without taking them off they returned to see the world to the right, seeing it inverted again when taking them off.

Samuel Serna Otalváro, 2019 OSA Ambassador, USA/France

Vision is a very complex process, where the visual system transforms light stimuli into information that is processed by the brain. The eyeball acts as an optical instrument, a camera: light coming from an object is first focused by the eye’s optics (cornea and crystalline lens) to form an image on the retina, which  detects photons of light, sample the light distribution, that later is absorbed and converted into chemical and electrical signals (visual signals) by the retinal layers. These signals exit the eye via the optic nerve and are transformed into cortical representations in the brain.

The information reaching the retina is upside down, because the process of refraction through a convex lens, the eye’s optics is around 60 D, causes the image to be flipped. But at the same time, the same optics allows to adjust extraordinarily to changes in the illumination, color, contrast, as well as having a large field of view, that with other optical design will not be possible. So, yes the image is upside down for a reason! But we do not see the world upside down…and the brain is responsible for that. We don't see images with our eyes. We see images with our brain. Essentially, the brain takes the raw, inverted data and turns it into a coherent, right-side-up image, thanks to its ability to  adapt the sensory information it receives and make it fit with what it already knows.

Maria Vinas, 2019 OSA Ambassador, Spain

EXPLORE
E C of USA asks...

How are telescope mirrors made?

Telescope mirrors are slowly and methodically polished using hard grinding tools, and even diamond. Some mirrors are made from glass substrates several meters in diameter and require smoothness to fractions of the thickness of a sheet of paper. For example, the Hubble Space Telescope's primary mirror had an aberration only 1/50th the size of a human hair. That aberration required astronauts to service the telescope, installing additional optics to correct the aberration while the instrument orbited nearly 550 km above the Earth.

Adam Fleisher, 2019 OSA Ambassador, USA

Making a single giant mirror for an optical telescope is not so easy: mirrors larger than 8 metres (26 feet) are extremely expensive and difficult to handle – even their own weight can cause the mirror to distort, making the image blurry. The solution to this is to use many smaller mirrors which have been shaped and aligned to form a giant mirror. For example, the European Extremely Large Telescope will be the world’s largest telescope, whose primary mirror will be formed of 798 hexagonal mirrors, each around 1.4 metres (4.6 feet) across, to produce a mirror wider than 39 metres (128 feet)!

The mirrors for the Giant Magellan Telescope are so big (7 mirrors, each 8.4 metres, or 27.5 feet) that they are being made underneath the University of Arizona’s football stadium! These mirrors are made by heating chunks of glass to more than 1,000°C (more than 2000°F) until they melt, and then are poured into a special mold which is spun around to give the correct shape. The glass is then cooled really slowly, over several months, to avoid it cracking. Finally, the surface is polished to give an extremely smooth surface, and the glass is given a reflective aluminium coating to turn it into a mirror.

Gabrielle Thomas, 2019 OSA Ambassador, Germany

EXPLORE
L B of Canada asks...

What other surface could be used to reflect light

Every object interacts with light in 3 possible ways: reflect, transmit, or absorb. Interestingly, if you see an object you are actually seeing which colors of light are reflected off the surface. So a red apple looks red because it's absorbing every other color except red which is reflected into your eyes.

Kimberly Reichel, 2019 OSA Ambassador, Italy

EXPLORE
L H of Canada asks...

How do some optical illusions look like there moving?

Watch this TED Talk by Beau Lotto! He amazingly explains and demonstrates how optical illusions "trick" our brain.

Kimberly Reichel, 2019 OSA Ambassador, Italy

EXPLORE
s p of USA asks...

how do you look at optical illusions.

Watch this TED Talk by Beau Lotto! He amazingly explains and demonstrates how optical illusions "trick" our brain.

Kimberly Reichel, 2019 OSA Ambassador, Italy

EXPLORE
J B of Australia asks...

Why do some optical illusions appear to move? Please answer soon

Watch this TED Talk by Beau Lotto! He amazingly explains and demonstrates how optical illusions "trick" our brain.

Kimberly Reichel, 2019 OSA Ambassador, Italy

EXPLORE
J F of USA asks...

Can you tell me how illusions work further? I’m writing an essay on illusions (my personal choice) and I’m needing information on how they work, what they do and why they work. Thanks!

Watch this TED Talk by Beau Lotto! He amazingly explains and demonstrates how optical illusions "trick" our brain.

Kimberly Reichel, 2019 OSA Ambassador, Italy

EXPLORE
M F of USA asks...

Why is it that I could be drawing and then look at the tv and it is blurry?

Your eyes have the ability to change focus, meaning to make clear an object close or far away. It is like when you watch someone with a camera that is rotating a tube on the front, they are doing this same thing which is changing the focus. As you are drawing, you are looking at something close to you and your eyes are focused at a short distance. When you look up to an object futher away, such as the TV, your eyes need to re-focus to make sharp the image at a far distance.

Kimberly Reichel, 2019 OSA Ambassador, Italy

EXPLORE
B J of Jamaica asks...

Why does the light bulb stay in your vision after staring at it for 25 seconds

Your eyes see light because of photoreceptors at the back of the eye. If you shine too much light for a long time on these photoreceptors they get "saturated" and so seem to remember the light you were just watching. As these photoreceptors relax again then the image goes away.

Kimberly Reichel, 2019 OSA Ambassador, Italy

EXPLORE
d M of Pakistan asks...

Explain,how light is reflected from objects?

Every object interacts with light in 3 possible ways: reflect, transmit, or absorb. Interestingly, if you see an object you are actually seeing which colors of light are reflected off the surface. So a red apple looks red because it's absorbing every other color except red which is reflected into your eyes.

Kimberly Reichel, 2019 OSA Ambassador, Italy

EXPLORE
C A of India asks...

HOW ARE ILLUSIONS MADE???

Watch this TED Talk by Beau Lotto! He amazingly explains and demonstrates how optical illusions "trick" our brain.

Kimberly Reichel, 2019 OSA Ambassador, Italy

EXPLORE
J N of USA asks...

how does The Animal Illusion work?

Watch this TED Talk by Beau Lotto! He amazingly explains and demonstrates how optical illusions "trick" our brain.

Kimberly Reichel, 2019 OSA Ambassador, Italy

EXPLORE
C S of UnitedKingdom asks...

If light shines on to a black/indigo surface, how can it produce the colour purple?

Every object interacts with light in 3 possible ways: reflect, transmit, or absorb. Interestingly, if you see an object you are actually seeing which colors of light are reflected off the surface. So an indigo surface looks indigo because it's absorbing every other color except indigo which is reflected into your eyes.

Kimberly Reichel, 2019 OSA Ambassador, Italy

 

EXPLORE
h r of USA asks...

how do people make optical illusions plus think the one with the gray dot when there actually there not a gray dot is pretty cool

During the second half of the nineteenth century, pioneers of experimental psychology, such as Delboeuf, Hering, Müller-Lyer, and others, discovered a wide variety of so-called optico-geometric illusions to which they gave their name. These are illusions formed by geometric figures, they give rise to errors of estimation, dimension, interpretations, curvature, direction ... There are also artistic optical illusions, which are not manifestations of errors of interpretation of the human visual system but rather the conception of the work that misleads our eyes.

Samuel Serna Otalváro, 2019 OSA Ambassador, USA/France

EXPLORE
L x of USA asks...

why do optical illusions always seem to move

The human eye gets tired very quickly when it is forced to stare at an object. If, on the other hand, the object's gaze is allowed to slip, it is thus avoided to fix too intensely and the image strikes other segments of the retina having their full capacity. The muscles of the eye allow not only to follow an object but also to perceive it exactly. It is also proven that there are movements when the latter strongly fixes an object. This is the reason why imaginary movements occur. The effects of movement arise when the remanent images conflict with those displaced by the movements of the eyes.

Samuel Serna Otalváro, 2019 OSA Ambassador, USA/France

EXPLORE
I S of USA asks...

What exactly goes on in the brain when we see illusions ?

Each brain is different. In fact, in humans, the physical mechanism for perceiving the information is the same in everyone: you use, for example, your eyes to capture visual information. The optical illusions appear when the visual system : eyes+brain makes a mistake in the interpretation. our eyes transmit an incredible amount of information to our brain. He must treat it to send us back an image. But for that, he uses simplifications, to help us see what is most important. This feature has no doubt helped the first humans to escape their predators, but today it is a perfect playground for optical illusions.

Samuel Serna Otalváro, 2019 OSA Ambassador, USA/France

EXPLORE
E F of Georgia asks...

How are prisms made?

In optics, a prism is an object, made of a transparent material, capable of refracting, reflecting and decomposing light in the colors of the rainbow (spectral content). Generally, these objects have the shape of a triangular prism, hence their name. In geometry, a prism is a polyhedron limited by two equal and parallel polygons called bases, and several parallelograms called side faces. Used in antiquity for its decorative side, in the form of pearls or to decompose the light, the prism knows its first rise as a scientific instrument during the late Middle Ages.

Samuel Serna Otalváro, 2019 OSA Ambassador, USA/France

EXPLORE
A Z of USA asks...

how to optical illusions work?

We see objects when light is reflected off of them. Our eyes have lenses (like spectacles) that capture this light and focus it at the back of the eye. The eye just collects the light, and sends it to the brain for processing via the optical nerve. The brain tries to interpret all the images that it receives. Sometimes the images can be made in such a way to 'trick' the brain. After all, the brain is trying to 'decode' all this new information that it receives and can interpret things slightly differently to what they are in reality!

Amol Choudhary, 2019 OSA Ambassador, Australia

EXPLORE
A X of Georgia asks...

When did you start wanting to be a Scientist?

I had always enjoyed studying science and reading about how things were made when I was growing up. However, I read the Brief History of Time by Stephen Hawking when I was in tenth grade and was fascinated by it. I think it was then that I realised that I wanted to be a scientist!

Amol Choudhary, 2019 OSA Ambassador, Australia

EXPLORE
M T of USA asks...

How big is the lab you work in?

60 M2 - the size of a small apartment!

Clara Saraceno, 2019 OSA Ambassador, Germany

EXPLORE
D g of Georgia asks...

why do we need optics

Think about your regular day. You wake up and open your eyes. Now you see the objects in your room. How do you see them? The light rays reflected from the objects enter your eyes and they pass through a tiny lens to form the images. This image formation process follows the principles of optics. If your vision is blurry, then you wear your eyeglasses to fix the problem. Such eyeglasses are also produced by using the principles of the optics. Then you look out your window and see that there is a rainbow. What a nice day! If you know that the rainbows are caused by the dispersion, reflection, and refraction of light in tiny water droplets, the day is even nicer to you! Because you observe a natural phenomenon on an ordinary day and since you know optics, you understand it better. Of course, you want to take a photo of this nice rainbow, you use your camera which is designed by using optics and it operates similar to your eye. Then you decide to go to the supermarket. All of your items have barcodes on them. At the checkout counter, a person scans your items by using a barcode scanner (Blip! Blip! Blip!). Scanning head shines light onto barcode, white areas of the barcode reflect more light than the black areas and the scanner easily identifies the item. This simple and time-saving process depends on the optics technology. Similarly, wireless technologies, CDs, virtual reality devices, sunglasses, 3D movies etc. they are all based on optics technologies. You might think that ‘okay, optics is useful for entertainment or every day works but what about the state of the art applications?’ By using optics-based technologies, scientists investigate gravitational waves (LIGO), build huge telescopes (Hubble), search for extraterrestrial intelligence (Optical-SETI), reveal ancient cities (Laser mapping), and diagnose diseases (optical coherence tomography). Without optics, our lives will be dull and our technologies will be incomplete.

Isinsu Baylam, Turkey, 2019 OSA Ambassador

EXPLORE
l k of Andorra asks...

what is a waveleghth

When you draw a wave, you picture it with top and bottom points. Wavelength is the distance between two identical bottom or top points. You can define a wavelength for an electrical signal or a light wave. For example, if you say that the wavelength of my laser pointer light is 532 nm (green), you mean that the distance between two crests of your electromagnetic wave (your light) is 532 nm. For an electromagnetic wave, wavelength of the light multiplied by the frequency (number of wave cycles per time) of the light gives you the fundamental and constant number of 300.000 m/s, the speed of light. Hence, if you have an electromagnetic wave with a longer wavelength, its frequency will be lower (such as radiowaves with wavelengths comparable to heights of mountains). On the other hand, if the wavelength is very short, the frequency of the electromagnetic wave will be higher (such as x-rays with wavelengths around nanometers).

Isinsu Baylam, Turkey, 2019 OSA Ambassador

EXPLORE
M B of Canada asks...

how was light made?

Light is both wave and particle. If you consider its wave nature, light undergoes constructive or destructive interference just like the water ripples. Different from the water waves, light is an electromagnetic wave similar to radiowaves, microwaves, UV, and x-rays. They have different names because we classify them according to their frequencies. If you think about its particle nature, light is made of photons. They are very very small particles which are always in motion at a speed of nearly 300.000 m/s and they carry the energy packets of the electromagnetic wave.

Isinsu Baylam, Turkey, 2019 OSA Ambassador

EXPLORE
J A of USA asks...

how long do you work a day

I am a lucky person because I have the job that I always wanted. So, during my hours at work, I do not count the ticks of the clock to go home. Of course, I have some regular duties such as meetings, trainings, and organizing research activities. Depending on the time of the year, a full workday is usually sufficient for me to finish my regular duties. When my duties are done, the fun part for me starts. I perform experiments up to late hours, read scientific papers about my research area or whatever area that I want, I attend seminars, and I study my undergraduate courses just to remember some important concepts again. If you are passionate about learning and you have that curiosity, you never stop. So, I cannot say that I am working exactly 8 hours every day because how many hours I work changes from day to day. Sometimes I finish my duties early and I start my experiments or reading activities early, sometimes I read/write about my research at home up to late hours.  The best advice is that choose a career path for yourself such that you feel happy while you work.

Isinsu Baylam, Turkey, 2019 OSA Ambassador

EXPLORE
G m of Rwanda asks...

What is the lens maker equation?

The focal length and focusing characteristics (diverging or converging) of a lens depends on the characteristics of the two spherical surfaces of the lens and the refractive index of the lens material. The lens maker equation can be used to obtain the focal length of a lens in terms of its refractive index and radii of curvature of its spherical surfaces. However, the equation is valid if you use a thin lens and if the media which surround the lens have the same refractive index at both sides of the lens. For a lens to be thin, the radii of curvature of its surfaces should be much larger than the thickness of the lens and so that you can assume that it is thin. It is a powerful equation because one can manufacture a lens with the desired focusing properties by selecting a suitable material and radii of curvature and it is widely used by lens manufacturers. In addition, the lens maker equation also provides information about the focusing power of the designed lens.

Isinsu Baylam, Turkey, 2019 OSA Ambassador

EXPLORE
D g of Georgia asks...

is it hard to be a scientist

Being a scientist is about having a passion for the understanding and development of science. When you have a passion for a subject you are driven to succeed and in that sense being a scientist is not difficult. It is important to identify where your passion lies.

Yaseera Ismail, South Africa, 2018 OSA Ambassador

EXPLORE
A H of USA asks...

what kind of equipment do you use to study light?

There are many different research activities that relate to the study of light and how light interacts with matter. And depending on which activity you work on, the instruments you use are going to vary. I like to build lasers and I use, for example, cameras to acquire images of the laser beam so I can properly measure how the beam looks like (the size, how the energy is distributed across the beam, etc). I also use something called a spectrometer, which is something similar to a prism (in fact, a prism may be part of a spectrometer), and allows me to study which colors my laser is made of. In the lab we use many other instruments, and somtimes we have to build our own instruments because we want to measure something that has not been measured before, so the instrument that we need does not yet exist.

Federico Furch, Germany, 2018 OSA Ambassador

EXPLORE
O H of Mexico asks...

Why is optics important

Optics is important as it provides an understanding of light and its uses. Optics can be explained by either physical optics or geometrical optics. Physical optics deals with the nature of light and its properties. Geometrical optics is the study of the path that is travelled by a ray of light in reflection, transmission and refraction. Optical instruments that you can relate to are telescopes, glasses, microscopes and fibre optics. We make use of optics daily in laser printers, cameras and communication just to name a few.

Yaseera Ismail, South Africa, 2018 OSA Ambassador

EXPLORE
k V of Azerbaijan asks...

How hot is the sun????

The Sun's core is about 27 million degrees Fahrenheit (15 million degrees Celsius).

The Sun is the largest and most massive object in the solar system. If the Sun were as tall as a typical front door, Earth would be about the size of a nickel.

It is about 93 million miles (149.5 million km) from Earth. That distance is called an astronomical unit, or 1 AU, and is used to measure distances throughout the solar system. The Sun's light and heat takes about eight minutes to reach us, which leads to another way to state the distance to the sun: 8 light-minutes.

The Sun is the center of our solar system and makes up 99.8 percent of the mass of the entire solar system.

Dr. Jelena Pesic OSA Ambassador Research Engineer, Bell Labs, NOKIA

EXPLORE
D F of USA asks...

How come in the demonstration with the water the question asks "Are the arrows going the same way" and if you look at the answer it says "No" why is this there it is actually wrong because if you move the glass the arrows are going the same way.

Thank you for your question as it caused a lively debate amongst the scientists. It really comes down to how you view the glass so we have updated the illusion to have a clearer question and we also changed the answer!

Dan Christensen, USA, 2018 OSA Ambassador

EXPLORE
k a of Georgia asks...

Is it fun being a scientist

Doing science as a job is like any other job or profession, in the sense that one has responsibilities, things that from time to time might stress you out, or that you don't like.

However, there is in my opinion something quite unique about being a scientist: You are all the time doing new things. You spend your time thinking about ideas that nobody thought of before, or inventing new devices and machines that can do things that were impossible before. In a sense, you are shaping the future and that is super exciting and fun.

Federico Furch, Germany, 2018 OSA Ambassador

EXPLORE
K C of USA asks...

How do optical illusions look like both of the images? How do you see both things??

This question iparticularly interesting because it combines both the fields of optics andcognitive science. Our brains are constantly guessing what we're looking at and trying to match it to something we recognize as an object. With these kinds of optical illusions, our brains are matching the image to multiple things it recognizes and can't decide what it is really looking at! This is a phenomenon called multistable perception.

Dan Christensen, USA, 2018 OSA Ambassador

EXPLORE