Rear View Mirrors: Objects Closer Than They Appear

[AlchemistK]

In rearview mirrors (convex mirrors) of vehicles it is stated that " Objects are closer than they appear".
But as we see in the ray diagrams of a convex mirrors, the image formed is closer to the mirror than the object so the image is closer than it actually wouldve have been in the case of a plane mirror, so it should have been that the objects are further away than they appear.

Yet the image we see is further away and the objects really are closer than they appear.(I tried it with an actual convex mirror)

Can anyone help me what is causing this??

 

[jtbell]

The image in a convex mirror is actually closer to you, but it is also much smaller than it would normally be, so your brain perceives it as being further away.

 

[AlchemistK]

So is the dimnished image formed enough to form the illusion of a further image?

 

[jtbell]

Yes. Suppose that you have a convex mirror with focal length -0.50 m, and an object with size 1.0 m is a distance 10.0 m from the mirror. Calculate the actual image location and size.

Now suppose you are standing a distance 1.0 m from the mirror (with the object 9.0 m behind you). What is the angular size of the image, as seen by you? How far away from you would it have to be, in order to have the same angular size, if it were 1.0 m high? (This is how far away it appears to be.)

 

[Buckleymanor]

The image in a convex mirror is actually closer to you, but it is also much smaller than it would normally be, so your brain perceives it as being further away.

It's daft when you ponder about this.
Surely it's a number of accidents waiting to happen,especialy if you havn't read the small print or interpreted it wrongly.

 

[Redbelly98]

Why do you say "waiting to happen"? Millions of these mirrors have been in use for several decades already. If, after all that time, we are still waiting for this to someday cause an accident, that only proves it is not a major problem.

If people need to gauge the distance to something accurately, I think they mostly look directly at it or use the central rear-view mirror (which is flat and does not distort the true distance). At least that's what I do.

 

[Buckleymanor]

Why do you say "waiting to happen"? Millions of these mirrors have been in use for several decades already. If, after all that time, we are still waiting for this to someday cause an accident, that only proves it is not a major problem.

If people need to gauge the distance to something accurately, I think they mostly look directly at it or use the central rear-view mirror (which is flat and does not distort the true distance). At least that's what I do.

I can't comment on the amount of accidents these mirrors have or havn't caused.So I at leaste don't know if these are or could become someones major problem.
It does seem silly though to be forced by some manufacturers to use a sight adjustment device.
Imagine if these same producers made it a requirement that everyone had to wear optical glasses to adjust there vision irrespective of the quality of there eyesight,before they were allowed to drive forewards in one of there vehicles.
It would be thought as ludicrous.
In effect though that is what they are imposing on drivers when they reverse.
If a driver can't see properly from a flat mirror he should get himself glasses not the car maker.

 

[Doc Al]

I can't comment on the amount of accidents these mirrors have or havn't caused.So I at leaste don't know if these are or could become someones major problem.
It does seem silly though to be forced by some manufacturers to use a sight adjustment device.
Imagine if these same producers made it a requirement that everyone had to wear optical glasses to adjust there vision irrespective of the quality of there eyesight,before they were allowed to drive forewards in one of there vehicles.
It would be thought as ludicrous.
In effect though that is what they are imposing on drivers when they reverse.
If a driver can't see properly from a flat mirror he should get himself glasses not the car maker.

Realize that convex mirrors are only used for the passenger side view mirrors. The driver side mirror and inside rear view mirrors are flat. The use of a convex mirror for the passenger side mirror was a breakthrough; it offers a wider field of view, making it much easier to spot other cars sneaking up on your outside.

 

[Buckleymanor]

Realize that convex mirrors are only used for the passenger side view mirrors. The driver side mirror and inside rear view mirrors are flat. The use of a convex mirror for the passenger side mirror was a breakthrough; it offers a wider field of view, making it much easier to spot other cars sneaking up on your outside.

Which if true just confuses the issue and makes it even more daft.
Here in the U.K. all three of our vehicles have convex mirrors on the passengers side and drivers side, the rear view mirrors all appear to be flat, except for the Range Rover, which I am not sure if it has a true image or not.
I presume you are referring to cars in the U.S.A. which if true when I visit I must remember to stick my neck out of the window and risk a cricked one.

 

[russ_watters]

It does seem silly though to be forced by some manufacturers to use a sight adjustment device...

Imagine if these same producers made it a requirement that everyone had to wear optical glasses to adjust there vision irrespective of the quality of there eyesight...

In effect though that is what they are imposing on drivers when they reverse.
If a driver can't see properly from a flat mirror he should get himself glasses not the car maker.

No, that's really not what is happening at all. The reason for the shape of the mirror has nothing whatsoever to do with the optics of you your eyesight, it is about the placement and geometry of the mirrors. In order to give you the same field of view with flat mirrors, they'd need to install more (or bigger) mirrors. These mirrors are not there to be "sight adjustment devices" like glasses, which obviously must be customized for each person's eyesight.

 

[Buckleymanor]

No, that's really not what is happening at all. The reason for the shape of the mirror has nothing whatsoever to do with the optics of you your eyesight, it is about the placement and geometry of the mirrors. In order to give you the same field of view with flat mirrors, they'd need to install more (or bigger) mirrors. These mirrors are not there to be "sight adjustment devices" like glasses, which obviously must be customized for each person's eyesight.

Sorry but any device that states.

" Objects are closer than they appear".

To my mind is some kind of sight adjustment device.
If you don't adjust reality to take into account of what you see when you are reversing you will crash.

 

[Redbelly98]

To my mind is some kind of sight adjustment device.
If you don't adjust reality to take into account of what you see when you are reversing you will crash.

Do you drive, yourself? It sounds like you don't. But if you do, how about an honest answer: what is your experience with these mirrors? Do you find them to be problematic when you actually use them?

From my experience, as an actual driver, I can tell you that these mirrors are not a hazard, and the wider field of view they offer is truly a help.

 

[Buckleymanor]

Do you drive, yourself? It sounds like you don't. But if you do, how about an honest answer: what is your experience with these mirrors? Do you find them to be problematic when you actually use them?

From my experience, as an actual driver, I can tell you that these mirrors are not a hazard, and the wider field of view they offer is truly a help.

Well if you bothered to read thread you would see that I mentioned we had three vehicles.
I suppose you could deduce from that I don't drive and just like to look at them.
As for problems when using these mirrors to be honest yes.

 

[Redbelly98]

Well if you bothered to read thread you would see that I mentioned we had three vehicles.
I suppose you could deduce from that I don't drive and just like to look at them.
As for problems when using these mirrors to be honest yes.

Fair enough. How many accidents have you had because of these mirrors?

 

[DaveC426913]

Buckley: your assumptions about the purpose of side view mirrors is in error. This is also incidentally causing you be driving improperly.

Side view mirrors are NOT for the purpose of determining the DISTANCE to an object. They are simply there so that the driver can determine IF there is an object there AT ALL.

If the mirrors were not convex, the field of view that they displayed of what is behind the driver would be so narrow as to be useless (I've done this, it's useless). There are only two ways to see a large field of view: make much larger mirrors (both impractical AND dangerous), or have small mirrors show a wider field of view.

As for problems when using these mirrors to be honest yes.

This makes sense. You are using them wrong.

Drivers manuals tell you that you do not TRUST your mirrors to give you the whole picture. It is your reponsibility to LOOK OVER YOUR SHOULDER.

 

[russ_watters]

Sorry but any device that states.
To my mind is some kind of sight adjustment device.
If you don't adjust reality to take into account of what you see when you are reversing you will crash.

I've never consciously adjusted reality when looking into a mirror but no doubt the wider field of view has helped. Under what circumstances have you found yourself making an adjustment and why? What would you suggest as an alternative to convex mirrors - huge mirrors on all cars?

I'm not going to argue about the definition of a term you made up: whatever you call them, they are very much unlike glasses.

 

[Buckleymanor]

Drivers manuals tell you that you do not TRUST your mirrors to give you the whole picture. It is your reponsibility to LOOK OVER YOUR SHOULDER.

Exactly couldn't agree more.So why the hell do car makers go to the bother of messing about with the field of view in the first place.
Do you reckon it might be a subtle ploy to force us into a position whereby we don't trust our mirrors and therefore this forces you to look over your shoulder.
Unfortunately the less subtle might not have read any manuals and expect to take what they see as expected.

 

[DaveC426913]

Exactly couldn't agree more.So why the hell do car makers go to the bother of messing about with the field of view in the first place.

You completely skipped over the salient bit, which answers your question quite nicely:

If the mirrors were not convex, the field of view that they displayed of what is behind the driver would be so narrow as to be useless (I've done this, it's useless). There are only two ways to see a large field of view: make much larger mirrors (both impractical AND dangerous), or have small mirrors show a wider field of view.

 

[Buckleymanor]

I've never consciously adjusted reality when looking into a mirror but no doubt the wider field of view has helped. Under what circumstances have you found yourself making an adjustment and why? What would you suggest as an alternative to convex mirrors - huge mirrors on all cars?

I'm not going to argue about the definition of a term you made up: whatever you call them, they are very much unlike glasses.

Frankly I was unaware that the rear view mirror is usualy a true image of what is viewed unlike the side mirrors which seem to vary depending on where you live.
I quite often drive relying more on this mirror than the side ones and now I know why.The field of view seems quite adequate.
Personaly I will rely more on the rear view mirror when reversing knowing that this will give me correct distances.I don't see why the side mirrors could not be flat to remove any confusion and if you needed a wider field of view then it should be up to the driver to look over his shoulder.
I could draw many similarities between the definition I described and glasses but I agree they are not the same.

 

[Redbelly98]

Personaly I will rely more on the rear view mirror when reversing knowing that this will give me correct distances.I don't see why the side mirrors could not be flat to remove any confusion and if you needed a wider field of view then it should be up to the driver to look over his shoulder.

I agree completely. If you don't know or understand the proper way to use a convex side-view mirror, then don't.

 

[DaveC426913]

I don't see why the side mirrors could not be flat to remove any confusion

Because you are trying to use them for a purpose for which are not intended. Stop before you kill someone.

 

[Buckleymanor]

Because you are trying to use them for a purpose for which are not intended. Stop before you kill someone.

Hey it's not me who is trying to kill someone.It is only recently that manufacturers have displayed on some of there side mirrors

" Objects are closer than they appear".

I imagine that the general public have been unaware that this is the case when using side mirrors and a majority are still unaware.
How many vehicles have this type of mirror and how many makers make this clear.

 

[DaveC426913]

Hey it's not me who is trying to kill someone.It is only recently that manufacturers have displayed on some of there side mirrors
I imagine that the general public have been unaware that this is the case when using side mirrors and a majority are still unaware.
How many vehicles have this type of mirror and how many makers make this clear.

You are the first person I've heard of who is having a problem with it.

Unless you have reason to suppose anyone else is, you're making a mountain out of a molehill.

 

[Buckleymanor]

You are the first person I've heard of who is having a problem with it.

Unless you have reason to suppose anyone else is, you're making a mountain out of a molehill.

Thats a bit rich after your last comment.

 

[Redbelly98]

(emphases added by Redbelly98)

It is only recently that manufacturers have displayed on some of there side mirrors

" Objects are closer than they appear".

No, they were doing this 25 years ago.

You didn't answer my earlier question. How many accidents have you had as a result of these mirrors?

 

[DaveC426913]

Thats a bit rich after your last comment.

How so?

 

[Buckleymanor]

(emphases added by Redbelly98)

No, they were doing this 25 years ago.

You didn't answer my earlier question. How many accidents have you had as a result of these mirrors?

I have three vehicles all manufactured after this time period and not one of them has this displayed.
One too many fortunately no one was injured.

 

[Buckleymanor]

How so?

Because I made the comment that it was my intention to use the rear view mirror look over my shoulder and also suguested that the side mirrors could be made in a similar way.
Your retort was to say to stop before I killed someone.
The last comment stop before I killed someone was making a mountain out of a mole hill.

 

[D H]

It is only recently that manufacturers have displayed on some of there side mirrors

" Objects are closer than they appear".

Only recently. Yeah, right.

 

[Redbelly98]

I have three vehicles all manufactured after this time period and not one of them has this displayed.
One too many fortunately no one was injured.

Are you sure these are convex mirrors?
Sorry to hear you had an accident, but frankly it is difficult to take some of the things you say seriously. I never use any mirror, even flat ones, to gauge where another car is if I really need to know that information. If I need to switch lanes or make a turn, I always look directly at the space where I want to go to, to see if anything is in the way.

 

[Buckleymanor]

Are you sure these are convex mirrors?
Sorry to hear you had an accident, but frankly it is difficult to take some of the things you say seriously. I never use any mirror, even flat ones, to gauge where another car is if I really need to know that information. If I need to switch lanes or make a turn, I always look directly at the space where I want to go to, to see if anything is in the way.

Absolutely you can see the difference quite clearly when looking at an object like a wall directly behind.
The two side mirrors show the wall to appear a further distance away than the rear view mirror.
Both the images in the side view mirrors appear to be at the same distance.
Done it checked it.

 

[DaveC426913]

The last comment stop before I killed someone was making a mountain out of a mole hill.

No it isn't.
1] That is not the appropriate expression for such a situation.
2] You are using the mirror incorrectly (as evidenced by the fact that you thought you could use them to judge distances and that you said you have had difficulties with using them this way), and that is dangerous.

suguested that the side mirrors could be made in a similar way.

They can't be made the same way. The geometry is all wrong. The rear view mirror is a foot from your face. The side view mirror can be as much as 3-4 feet from your face. This makes for a useless field of view.

 

[Buckleymanor]

No it isn't.
1] That is not the appropriate expression for such a situation.
2] You are using the mirror incorrectly (as evidenced by the fact that you thought you could use them to judge distances and that you said you have had difficulties with using them this way), and that is dangerous.

O! yes it is you made a total exageration and was a bit rude too.

They can't be made the same way. The geometry is all wrong. The rear view mirror is a foot from your face. The side view mirror can be as much as 3-4 feet from your face. This makes for a useless field of view.

What do you drive a crane.The geometry in my vehicles is OK.
The distance from my face to one of the side view mirror is about the same as the distance to the rear view mirror.
Even if it wasn't both mirrors could be positioned so they were, even in your crane.

 

[Doc Al]

The distance from my face to one of the side view mirror is about the same as the distance to the rear view mirror.

The distance to the passenger side mirror is much farther than the distance to either the driver's side mirror or the rear view mirror. More importantly, the angle is such that you need a wider field to see what's coming.

And what are you doing using your mirrors when backing up? Please turn your head and look behind you! (Only in some special cases will I back up using my center mirror--like backing into my garage. But that's it.)

Please stay off the road until you understand how to use your mirrors.

 

[Buckleymanor]

The distance to the passenger side mirror is much farther than the distance to either the driver's side mirror or the rear view mirror. More importantly, the angle is such that you need a wider field to see what's coming.

And what are you doing using your mirrors when backing up? Please turn your head and look behind you! (Only in some special cases will I back up using my center mirror--like backing into my garage. But that's it.)

Please stay off the road until you understand how to use your mirrors.

Just what I expected here is the original post.

They can't be made the same way. The geometry is all wrong. The rear view mirror is a foot from your face. The side view mirror can be as much as 3-4 feet from your face. This makes for a useless field of view.

No need to correct me Dave said and I repeat .The side view mirror can be as much as 3-4 feet from your face.He don't state if it's one or the other side mirrors.
Reckon you should stay of the road until you can read.

 

[DaveC426913]

Reckon you should stay of the road until you can read.

Well somebody's feeling a little wounded...

 

[DaveC426913]

The distance from my face to one of the side view mirror is about the same as the distance to the rear view mirror.

Sorry, I'll spell it out.

Distance is one factor. The other factor is how wide a field of view you need. While it is true that the driver's side mirror is the same distance as the rearview mirror, the requirement for field of view is not the same. Rearview mirror need only show what's directly behind you. Driver's side mirror needs to show everything from your left bumper all the way to the edge of your peripheral vision. This is much wider, and will not be captured by a flat mirror.



(P.S. The difficulty I'm having with you is that you are quick to judge (calling maufacturers "daft") without knowing the purpose or process that led to a design, and do not stop to ask yourself if maybe a hundred years of evolutionary design has given them a modicum of wisdom. I'd be much easier on you if you showed some humility. First, assume people know what they're doing; judge only as a last resort.)

 

[Buckleymanor]

Sorry, I'll spell it out.

Distance is one factor. The other factor is how wide a field of view you need. While it is true that the driver's side mirror is the same distance as the rearview mirror, the requirement for field of view is not the same. Rearview mirror need only show what's directly behind you. Driver's side mirror needs to show everything from your left bumper all the way to the edge of your peripheral vision. This is much wider, and will not be captured by a flat mirror.



(P.S. The difficulty I'm having with you is that you are quick to judge (calling maufacturers "daft") without knowing the purpose or process that led to a design, and do not stop to ask yourself if maybe a hundred years of evolutionary design has given them a modicum of wisdom. I'd be much easier on you if you showed some humility. First, assume people know what they're doing; judge only as a last resort.)

Appreciated though I am trying to get some points across even if I am a bit judgmental.
Earlier in the thread it was mentioned that the drivers side mirror was flat and it was only the passengers side that was convex.
It was pointed out that in the U.K. at least this was not the case and I have a sneaking suspicion that the same applies in the U.S.A.
In effect both side mirrors are convex and with the passengers mirror 3-4 feet further away than the other mirrors does this not cause a certain amount of inconsistency with your argument.

 

[DaveC426913]

In effect both side mirrors are convex and with the passengers mirror 3-4 feet further away than the other mirrors does this not cause a certain amount of inconsistency with your argument.

It's not an inconsistency, it's an interplay between three parameters for the sake of one end result.

Simply put: field of view is the fixed, required end result. The interplay of three parameters will achieve this: the size of the mirror, its distance and its convexity.

Size and distance are factors that are optimaized - but only up to the constraints of the geometry dictated by the car itself. If the FoV is still not met, the only thing left to do is change the optics of the mirror(s) as needed.

 

[Buckleymanor]

Sorry, I'll spell it out.

Distance is one factor. The other factor is how wide a field of view you need. While it is true that the driver's side mirror is the same distance as the rearview mirror, the requirement for field of view is not the same. Rearview mirror need only show what's directly behind you. Driver's side mirror needs to show everything from your left bumper all the way to the edge of your peripheral vision. This is much wider, and will not be captured by a flat mirror.

So to clear things up are the drivers side mirrors in the U.S. convex like the passengers and not flat.Unlike an earlier post that said they were.
If they are convex do they take into account that they are nearer to the driver than the passengers side mirror and have slightly different optics, to allow for the factor of distance.

 

[Doc Al]

So to clear things up are the drivers side mirrors in the U.S. convex like the passengers and not flat.Unlike an earlier post that said they were.
If they are convex do they take into account that they are nearer to the driver than the passengers side mirror and have slightly different optics, to allow for the factor of distance.

All the drivers side mirrors I've seen (in the US) have been flat, not convex. (Although a double mirror is not uncommon, where the smaller top part is convex while the main part is flat.) Only passenger side mirrors are convex.

 

[pallidin]

All the drivers side mirrors I've seen (in the US) have been flat, not convex. (Although a double mirror is not uncommon, where the smaller top part is convex while the main part is flat.) Only passenger side mirrors are convex.

Driver side flat mirror is necessary for accurate distance perception.
Passenger convex mirrors are only intended for "enhanced angular view", NOT for driving while looking at them.

Basically, the convex mirrors, though producing a distorted distance image, allows a "threat" observation only. Do not try to change lanes while only viewing a convex mirror. Do, however, glance at that to determine your threat environment.

 

[Buckleymanor]

All the drivers side mirrors I've seen (in the US) have been flat, not convex. (Although a double mirror is not uncommon, where the smaller top part is convex while the main part is flat.) Only passenger side mirrors are convex.

Can this be true.
Daves allready stated.

You completely skipped over the salient bit, which answers your question quite nicely:


If the mirrors were not convex, the field of view that they displayed of what is behind the driver would be so narrow as to be useless (I've done this, it's useless).

And

The difficulty I'm having with you is that you are quick to judge (calling maufacturers "daft") without knowing the purpose or process that led to a design, and do not stop to ask yourself if maybe a hundred years of evolutionary design has given them a modicum of wisdom. I'd be much easier on you if you showed some humility. First, assume people know what they're doing; judge only as a last resort.)

Driver's side mirror needs to show everything from your left bumper all the way to the edge of your peripheral vision. This is much wider, and will not be captured by a flat mirror.

Me thinks someone else should show a modecum of humiliation.

 

[Doc Al]

Can this be true.

It's true. What pallidin stated in post #42 is essentially correct. (See: http://www.garamchai.com/askadesi/ask07.htm" ; it seems accurate to me.)

Daves allready stated.

Dave's statement about driver-side mirrors in the US being convex is incorrect.

In my experience, most folks do not know how to adjust their (flat) driver-side mirror to eliminate most of the blind spot. When you glance at your driver-side mirror you should not see the side of your car.