Understanding Reflection of Light on a Concave Mirror

[SHASHWAT PRATAP SING]

The entire time, you seem to make the point that the person in the image, i.e. the object, is the one making the observation. This is clearly wrong!

Ok, Does this mean the person seeing in the concave mirror will see something different than us...

t is why knowing what's what is important. The camera that made that images here are NOT from real images, i.e. the light rays are diverging. They are from virtual images of that person (object).

What Does this mean ?
When the object (guy) is outside the focal length the image is real.

 

[hutchphd]

I am saying that if the camera were in the man's eye socket we would not see an image for the part of the trip between cc and focal point. There will be an image formed that is inaccessable to camera view.

 

[SHASHWAT PRATAP SING]

I am saying that if the camera were in the man's eye socket we would not see an image for the part of the trip between cc and focal point. There will be an image formed that is inaccessable to camera view.

I mean that the Real image what we are seeing-

And what the person is seeing in the concave are they both different-

Will this person(Object) see something different than us ?
Please tell this...

 

[A.T.]

I am saying that if the camera were in the man's eye socket we would not see an image for the part of the trip between cc and focal point.

Not an image at all for the entire range between cc and focal point? Or just not see a sharp image? Assuming a camera that can focus converging rays on the sensor (or a pinhole camera), would it not see an image like shown in the diagram?

 

[SHASHWAT PRATAP SING]

Not an image at all for the entire range between cc and focal point? Or just not see a sharp image? Assuming a camera that can focus converging rays on the sensor (or a pinhole camera), would it not see an image like shown in the diagram?

A.T. please reply me at my post-#63

 

[SHASHWAT PRATAP SING]

I am saying that if the camera were in the man's eye socket we would not see an image for the part of the trip between cc and focal point. There will be an image formed that is inaccessable to camera view.

hutchphd please reply me at my post-#63

 

[SHASHWAT PRATAP SING]

You really need to work on your description. Say exactly what you mean. Say exactly what each picture shows.

Try to avoid phrases like "image must be forming". If you are standing still the image is either there or it is not. It is not "forming". Try to avoid phrases like "real image in the mirror". The real image is not in the mirror. It is behind your head.

You have provided a number of pictures. Let us go through them slowly. Let us identify carefully what they show.

The first picture is of someone standing nose to mirror. There are two locations marked on the floor. One is marked "C". One assumes that this is at the center of curvature of the concave mirror. The other is marked "F". One assumes that this is at the focal length of the concave mirror.

This impression is reinforced by the fact that the distance from the mirror to C is approximately double the distance from the mirror to F.

But you are not asking about the situation in the first picture. So that picture is mostly wasted.The second picture is of someone standing between the focal point F and the center of curvature C. We see a blue shape drawn in space behind the person. One assumes that this is the place where the [inverted] real image of the person would form.

The person stands in the way of some of the reflected light that might otherwise go into forming this real image. As a result, the real image may not be viewable from all angles. However, this detail is irrelevant to the question that we are trying to address. Let us ignore that situation and proceed.The third picture is the same as the first but without the "C" and "F" labels drawn in. We can ignore it.The fourth picture is the same as the second. But instead of "C" and "F" labels and an image drawn behind the person, we have an arrow in front of him pointing toward the mirror.

This would appear to be an attempt to depict the person's line of sight toward the mirror.The final picture appears to have been taken from a little to one side as the man stands in the position depicted in the second and fourth pictures. That is, it was taken while the man is standing between the C and the F. It shows an inverted image.

This appears to be an attempt to show what the person himself sees. I may be mistaken, but that might be the camera's reflection in the person's right hand.If I understand your concern, it is that if we are looking away from a real image, we might not expect to be able to see that image. Certainly, our intuitive expectations learned from everyday life tend to support this. If person is standing behind me, I cannot see them when I am looking toward the front. If an image exists behind me, I might not expect to see it when I am looking toward the front.

This expectation is incorrect. The photographic evidence you have provided demonstrates that it is incorrect.

The light rays that hit your eyes are light rays that would have converged at the real image behind your head. But they did not converge there. Your eyes were in the way. The lens in your eyes (or in your camera) caused them to converge on your retina (or on the photodetector array in your camera) instead.

You "see" the image because the pattern of illumination on the retina (or on the photodetector array) corresponds to the shape of the person.

Human eyes are not designed to be able to clearly image converging light rays. It requires that they relax to a focal length longer than the distance from lens to retina. A focal length equal to the retinal distance would allow one to clearly focus on objects "at infinity". A shorter focal length allows one to focus on objects closer in. A longer focal length allows one to focus on images corresponding to convergent light rays -- that is real images behind the head.

There is no evolutionary call for eyeball lenses that can focus out past infinity. And little technical call for cell phone lenses that can do the same. The cell phone image of the reflected inverted man is not sharp. But with a narrow aperture, one can push the limits.

As jbriggs444 said, I think this is what happening in this case

 

[hutchphd]

Not an image at all for the entire range between cc and focal point

When I say image I mean that light from each point in the the object plane will be found at only one point in the image plane. This is a geometric optics construction (no diffraction limits) and assumes a perfect lens/mirror. With this (correct) definition for an image the statement stands. If you want to talk about fuzzy images and depth of field and circles of confusion that is fine, but it is a different and largely distinct conversation.

 

[SHASHWAT PRATAP SING]

The light rays that hit your eyes are light rays that would have converged at the real image behind your head. But they did not converge there. Your eyes were in the way. The lens in your eyes (or in your camera) caused them to converge on your retina (or on the photodetector array in your camera) instead.

You "see" the image because the pattern of illumination on the retina (or on the photodetector array) corresponds to the shape of the person.

As jbriggs444 says I think this is what happening in this case-

Please tell

 

[A.T.]

When I say image I mean that light from each point in the the object plane will be found at only one point in the image plane.

Replace the eye in my diagram with a camera that has a flat sensor at the back and a lens that creates an image in the plane of the sensor. Why couldn't this camera record a sharp picture?

 

[jbriggs444]

As jbriggs444 said, I think this is what happening in this case

After thinking further, the fact that you see an inverted image is relevant and indicates that the person is not actually positioned between the center of curvature (C) and the focal point (F).

If the person were positioned between C and F the resulting image would be real, would be positioned on the far side of the C and would be inverted. Rays coming from the person's head would arrive at the bottom of the image. Importantly, this means that they would arrive at a downward angle. Rays coming from the person's feet would arrive at the top of the image. Importantly, this means that they would arrive at an upward angle.

But your eyes are in the way. They intercept these rays. Instead of an inverted real image forming in space to the left of the C, these rays would form an inverted real image on your retina. The rays from the person's feet would arrive at an upward angle and would illuminate the top of the retina. The rays from the person's head would arrive at a downward angle and would illuminate the bottom of the retina.

But an inverted real image on your retina is what you get when looking at an ordinary upright person. If the scenario were actually as you describe, the image you perceived and the image that your camera perceived would have both have appeared to be upright.

Accordingly, I must retract my earlier analysis and conclude that you are actually standing to the left of the C and that the real image is in front of you.

 

[hutchphd]

Replace the eye in my diagram with a camera that has a flat sensor at the back and a lens that creates an image in the plane of the sensor. Why couldn't this camera record a sharp picture?

Perhaps.
I think that (as was shown by the Hubble fix) one could likely create a thick lens that would allow a correction at a particular point along the path. But it would not be an imaging system in the normal sense of the word. The optics would image a "virtual object" I think. A negative lens in front of the camera might suffice.
Need to think a little more...maybe not today!

 

[A.T.]

I think that (as was shown by the Hubble fix) one could likely create a thick lens that would allow a correction at a particular point along the path. But it would not be an imaging system in the normal sense of the word.

It seems you would need a thinner lens than usually, because the rays are already converging. You just have to shift the convergence plane from behind the camera to the sensor.

The optics would image a "virtual object" I think.

It looks like an intermediate case: The rays used by the camera would form a real image, but they are captured, so just like with virtual images they are never focused (outside of the camera).

 

[SHASHWAT PRATAP SING]

After thinking further, the fact that you see an inverted image is relevant and indicates that the person is not actually positioned between the center of curvature (C) and the focal point (F).

If the person were positioned between C and F the resulting image would be real, would be positioned on the far side of the C and would be inverted. Rays coming from the person's head would arrive at the bottom of the image. Importantly, this means that they would arrive at a downward angle. Rays coming from the person's feet would arrive at the top of the image. Importantly, this means that they would arrive at an upward angle.

But your eyes are in the way. They intercept these rays. Instead of an inverted real image forming in space to the left of the C, these rays would form an inverted real image on your retina. The rays from the person's feet would arrive at an upward angle and would illuminate the top of the retina. The rays from the person's head would arrive at a downward angle and would illuminate the bottom of the retina.

But an inverted real image on your retina is what you get when looking at an ordinary upright person. If the scenario were actually as you describe, the image you perceived and the image that your camera perceived would have both have appeared to be upright.

Accordingly, I must retract my earlier analysis and conclude that you are actually standing to the left of the C and that the real image is in front of you.

From this, I understand that for us (our eyes or the camera) The real image of the man is formed in front of us
than what about the person(object) standing between the centre of curvature and focus.
Does this mean the person seeing in the concave mirror would see a different Real image of himself than us.
What would the person see here from his perspective...Please tell.

 

[A.T.]

What would the person see here from his perspective...Please tell.
View attachment 265811

My guess: A big blurry but not flipped image of himself.

In the video below (after 4:45) they move the camera towards the mirror. They claim the flip in the camera picture happens happens at F. But as I explained in post #35 the camera picture should flip at C, and not be flipped between C and F.

 

[SHASHWAT PRATAP SING]

My guess: A big blurry but not flipped image of himself.

Whattttttt How...?
From the rules of image formation in a concave mirror we know that-
When an object is placed between focus and the centre of curvature
A real and inverted image is formed beyond C.
then How can the person here standing between centre of curvature and focus from his perspective see a big blurry image, which is even not flipped how...?

 

[A.T.]

How can the person here standing between centre of curvature and focus from his perspective see a big blurry image, which is even not flipped how...?

See posts #35 and #71. Keep in mind that if the real image on the retina is flipped, then we see a not flipped picture. It's blurry because our eyes are trained for focusing diverging to parallel rays, not for the converging case.

 

[sophiecentaur]

How can the person here standing between centre of curvature and focus from his perspective see a big blurry image, which is even not flipped how...?

Look more carefully. The image you see will be blurry (of course) but it goes from inverted to non-inverted as you move either side of the exploding point. I really believe you are looking for something 'magic' about this rather than a rational explanation of a repeatable and identifiable situation. The only paradox is in the way you are assessing what you see.
Again, have you actually tried the spoon experiment?

 

[SHASHWAT PRATAP SING]

Look more carefully. The image you see will be blurry (of course) but it goes from inverted to non-inverted as you move either side of the exploding point. I really believe you are looking for something 'magic' about this rather than a rational explanation of a repeatable and identifiable situation. The only paradox is in the way you are assessing what you see.
Again, have you actually tried the spoon experiment?

sophiecentaur I have done that.Please read my post-#74 which is what I am confuse about...

Does this mean the real image what we are seeing and what the man is seeing is different.
would the person seeing in the concave mirror see a different Real image of himself than us ?

 

[SHASHWAT PRATAP SING]

Looking at that diagram again: Since the real image on the retina is flipped, you should see yourself not flipped in this case. Assuming your eye can still focus these rays.

So the distance at which the image on your retina flips, is not the focus point but the center of curvature. The focus point is merely the distance at which the not flipped virtual image behind the mirror is replaced by a real image behind you.

A.T. does this means that when the person is near the focus of the concave mirror he would see a big blurry but not flipped image of himself but as the person slowly moves backward when he is near the centre of curvature he would see a flipped and real image of himself in the concave mirror ?

 

[sophiecentaur]

Does this mean the real image what we are seeing and what the man is seeing is different.
would the person seeing in the concave mirror see a different Real image of himself than us ?

If we were in a different place then we would see a different image - OF COURSE. (There - now I am shouting). People see what they see, by the image on their retina and the light entering it. That image may or may not be in focus. The blurry image around the exploding zone will never be sharp for the man. If he put a correcting lens (convex) between his eye and the mirror, he could bring an image to a point in front of him and he would see it sharp but the lens would have to be way in front of him so that the image would be real, between him and the lens and beyond his 'near point'.

You say you have used a spoon but made no comment about what you saw. So I cannot comment on that but it's fairly crucial. Also, you ask @A.T. what the man 'would see'. What do you see?
If you have never done the experiment then use (borrow) a make-up /shaving mirror, if the spoon doesn't convince you.

 

[Vanadium 50]

Can we stop the bolding? If everything is bolded, nothiong is.

 

[SecularSanity]

Summary:: Please Explain me this problem in detail...

My Basic Question is-
Why can we see our inverted and real image inside a concave mirror when the image is formed in front of it and not behind?

If you say that our eyes tries to image the real image formed by mirror on the mirror itself then-

Imagine a situation where we have a concave mirror of large size and we ourself is object and we are directly seeing in the concave mirror and moving backwards so when I stand between focus and pole I see my virtual image slowly when I move backward between focus and centre of curvature then my image must be forming behind me then how my eyes are able to see my real image in the mirror….

Sir to image the real image my eyes must see the image first but in this case how without seeing the image my eyes can see the real image in the mirror it self HOW IS IT HAPPENING …..
Consider this video on youtube -https://youtu.be/7zv-4Zh-9R4

Please answer me in detail... sir i am eagerly waiting for answersView attachment 265660

A real image is seen when the light rays themselves actually converge. A virtual image is seen only where the light rays appear to converge. In other words, a virtual image is made when our eyes trace the rays back behind a mirror or lens. When you’re close to the concave mirror, between the focal point and the mirror, it’s a virtual image. The image will be upright and magnified. A real image is inverted and a virtual image is upright.

Your diagram is what’s confusing you. They’re not indicating that the image is formed behind you. They’re showing you the linear (sometimes called lateral or transverse) magnification equation.

 

[SHASHWAT PRATAP SING]

Your diagram is what’s confusing you. They’re not indicating that the image is formed behind you. They’re showing you the linear (sometimes called lateral or transverse) magnification equation.

SecularSanity please read my post-#63 and help me...

 

[SecularSanity]

SecularSanity please read my post-#63 and help me...

They’re not indicating that the object is behind. They’re showing you the magnification relative to the distance.

 

[SHASHWAT PRATAP SING]

A.T. and hutchphd please reply at my post-#80

 

[sophiecentaur]

Keep in mind that if the real image on the retina is flipped,

IMO, that's a red herring. The same thing happens with all images and all rays entering the eye. Light coming in from above the horizontal always hits the lower half of the retina.

A.T. does this means that when the person is near the focus of the concave mirror he would see a big blurry but not flipped image of himself but as the person slowly moves backward when he is near the centre of curvature he would see a flipped and real image of himself in the concave mirror ?

Why do you keep asking what someone 'would see'? If you have done the experiment (and everyone has a spoon) then the question should be 'why do I see. . . . . ..?' Do you not have access to a shaving / makeup mirror or are you, in fact a bot, coming up with the same question again and again just to wind us all up?

 

[SHASHWAT PRATAP SING]

IMO, that's a red herring. The same thing happens with all images and all rays entering the eye. Light coming in from above the horizontal always hits the lower half of the retina.Why do you keep asking what someone 'would see'? If you have done the experiment (and everyone has a spoon) then the question should be 'why do I see. . . . . ..?' Do you not have access to a shaving / makeup mirror or are you, in fact a bot, coming up with the same question again and again just to wind us all up?

I am asking the same question again and again because I am confused with this post-

The man is describing what the camera (you) are seeing not what he is seeing. He cannot see the image when it is behind his head. The camera is well beyond the center of curvature. Not a great video.

I have done the spoon experiment but in that I cannot place myself between the centre of curvature and focus of the spoon as it is at a very small distance. Due to which I am not able to understand what happens when we approach the centre of curvature and focus of the concave mirror.

The man in this video Talks as he is also seeing the same thing what we are seeing, sophiecentuar please see this video between 1:40 to 2:00


Sophiecentuar I really thank you for being engaged with me for this. ...really Thanks from my heart.

 

[sophiecentaur]

I have done the spoon experiment but in that I cannot place myself between the centre of curvature and focus of the spoon as it is at a very small distance.

I just did it. At a distance, you see yourself a long way off, upside down. You go in close and you see your eyeball the right way up. In between, there's the explosion and you see nothing because the image of your eye is behind you at first, then too near your eye to focus and then, there it is. You can tell it's the right way up when you blink.
Probably a teaspoon would be too small but I used a tablespoon and a soupspoon (spherical and better). Better still, a shaving mirror - or visit a funfair hall of mirrors.

I think you may be having a problem with confidence about understanding that video. Whatever you manage to make of it, the theory is supported by what you can actually see for yourself so you do not have to work too hard to reconcile what the guy says in the video. He is just peripheral to the real issue.
Quite frankly the video is very bad. If he wanted to show you what he was actually seeing then he should have carried the camera with him. As it is, he's actually lying to you about what he and the camera see! He's not too sharp, actually. He started off mixing up convex and concave names and then he fell over his floor marker - duh! Not worth worrying about it. Just repeat the experiment with the spoon and see your eye invert after the exploding region. Admittedly you don't see your eye in focus, up close (unless you have very strong accommodation muscles) but when you can see an image, it HAS to be in front of you.

Don't forget. You are not obliged to believe what you are shown in any video when it clearly doesn't make sense.

 

[hutchphd]

The man in this video Talks as he is also seeing the same thing what we are seeing, sophiecentuar please see this video between 1:40 to 2:00

The image he is seeing between the focal point and cc, if he has normal vision, not a clear image (it is very fuzzy and mostly indecipherable. If he is very farsighted (hyperopic) he will be able to` cheat the cc point a little.

Indeed using a negative (concave) lens one could devise a eyeball camera that could provide an in focused view for the man in the region between focal point and cc. It would not otherwise be useful, so we are better off with the cameras and eyeballs we have which work as @sophiecentaur just described and do not work well in that region.

Two things to take away: (1)an optical image means a very particular ideal one to one mapping...almost an image is not an image and (2) not all books/videos/teachers are worth your energy

If you can find a decent small mirror give it a go...nothing better than good play session. Good Luck