Rear-View Mirrors

On Feb 2, 9:21*pm, wrote:
Frank Krygowski wrote:
In an ordinary, full-sized mirror (like, say, a dressing room
mirror) depth perception works exactly as it does with no mirror.
At close range (up to, say, 20 feet) depth is judged partially by
parallax (the difference in image perceived by your left and right
eye) and partially by perspective (the reduction in image size at
greater distances). *It doesn't matter if the image you're seeing is
in a mirror or not.

Oh ****.

Control yourself, Jobst. You don't want to get an e-mail criticizing
your posting style.

*We've been here many times on wreck.bike in the past. *Your
assessment is entirely wrong and has been tested often.

It's been tested countless times. I can test it now sitting in my
living room. I can tell that the computer screen is closer than my
shoe, which is closer than the candlestick, which is closer than the
fireplace... and the parallax effect is obvious. You can't see those
sorts of things?

Persons who believed this scenario were used for the test in which
their head was held in a "vise" that prevented head movement...

No head movement was needed for those judgments above.

... when
shown objects on a featureless plane at various distances from the
observer. *Those tested, could not tell anything about the relative
distances of the objects because the way humans assess distance in
depth is by relative motion when the position of observation changes,
either by the person moving or by moving just the head.

Sorry, you're wrong, at least for a certain range of distances.
There's an old parlor trick that involves having a person try (and
fail) to touch an object close to them with one of their eyes closed.
I just replicated it by failing to touch the corner of this new
computer, because one of my eyes was closed. Readers - or
contentious posters - can try it themselves.

At greater distances, parallax doesn't work. Motion helps, and so
does familiarity with the sizes of objects - but neither is hampered
by use of one eye, as with an eyeglass mirror.


Please do not perpetuate the old myth of binocular range finding with
human eyes. *You can do that with optical instruments, but not alone
with eyes.

It's a popular "myth"! It seems to be popular with ophthalmologists,
psychologists, biologists, and vision specialists of all stripes.
http://www.vision3d.com/stereo.html
http://en.wikipedia.org/wiki/Depth_perception
http://health.howstuffworks.com/eye10.htm

I don't know why you argue against something that is so easily
demonstrated!

With a one-eyed eyeglass mirror, parallax is no help; but you still
see the perspective effect. *It's easy to judge things like the
approach of a car, or the approach of a useful gap in traffic.

It's unclear what you mean by "perspective effect."

When things are further away, they appear smaller in your field of
view.


At least, it's easy for me. *YMMV, I suppose.

You are fooling yourself as did those in the test, who were sure they
cold range find with their eyes alone... and couldn't without relative
motion, the effect humans, and others, use to assess relative
distance.

Close one eye and touch your monitor's top corner.

Convex mirrors do have detriments, in that they mess with the
perspective component of depth. *"Objects in the mirror are closer
than they appear." *OTOH, they have benefits too: wider field of
view, and less trouble from vibration. *One of my motorcycles and
all the cars I drove in Europe had convex side view mirrors. *It's
certainly possible to adapt to them.

Are you making this up "on the fly" or where did you learn this?

Let's see, do you mean the part about convex mirrors having a wider
field of view? Or about their being on the cars I drove in Europe?
Or about the effect on vibration? Which of those don't you believe?

*The mirror is visible
through the upper portion of the glasses lens. *It's no problem at
all.

Of course. *Mirror distance has no effect, although distance to the
object does, but traffic is sufficiently far away and has motion.

Obviously, the distance of the mirror has no effect on focus. It has
no effect on depth perception via parallax, as long as one can use
both eyes. The eye treats the length of the reflected rays
(i.e.object to mirror to eye) the same as direct rays passing through
a window.

There is an effect of mirror distance, though; that's field of view.
A small mirror close to the eye gives a field of view equal to that of
a larger mirror placed further from the eye - again, exactly like a
window - or a peephole. Bear that in mind when you design your own
eyeglass mirror.

- Frank Krygowski

On Feb 2, 10:43*am, "Roger Zoul" wrote:
"landotter" wrote in message news:gm1pt7
Don't you have ears? Use 'em. Experienced cyclists can tell what cars are
doing behind them by listening.

Nonsense. *I have been in plenty of situations where I could not even hear a
car coming up behind me.

I
How stoned were you? I only worked a short time as a bike messenger,
but it learned me many things. You can feel traffic via sight, sound,
and even good ole vibration. If a car was too close to me on Michigan,
I could feel it in my toes.

::: Don't you have ears? Use 'em. Experienced cyclists can tell what
::: cars are doing behind them by listening.
landotter

::
:: Nonsense. I have been in plenty of situations where I could not even
:: hear a car coming up behind me.
Roger Zoul"


: Ilandotter wrote:

: How stoned were you? I only worked a short time as a bike messenger,
: but it learned me many things. You can feel traffic via sight, sound,
: and even good ole vibration. If a car was too close to me on Michigan,
: I could feel it in my toes.

So, you're saying you never ride out in the countryside like the rest of us?
Never out in the wind or along a winding road? You don't "feel vibration"
out on Farm to Market roads in Texas.

The whole world ain't downtown.

Pat in TX

Roger Zoul wrote:
"landotter" wrote in message news:gm1pt7
Don't you have ears? Use 'em. Experienced cyclists can tell what cars are
doing behind them by listening.


Nonsense. I have been in plenty of situations where I could not even hear a
car coming up behind me.

It's amazing what crap people write in the internet when they don't have to
be accountable for any of it.

It's not just that, it's what they write when they have no idea of what
they're talking about! The attitude about mirrors seems to be a
knee-jerk reaction against them, even when they've never used them. The
classic response in this thread was from someone who wrote about how
distracting they were and how they blocked your field of view and how he
hated them, but preceded those pearls of wisdom with a statement of how
he had never used one.

Personally I think they should be required equipment, as they greatly
increase safety. I read that bicyclists with mirrors are 60% less likely
to be in an accident. Mirrors should be considered as important as
lights at night.

The Portland (OR) Department of Transportation has a publication on
bicycle safety and writes:

Equipment solutions to improve bicycle safety:

The toolbox of solutions to improve bicycle safety includes equipment
measures, such as the following:
- Mirrors on vehicles, including bicycles, to improve visibility and
reduce or eliminate blind spots
-Metal plates and guide bars to prevent people from going under vehicles
-Reflective signs warning people not to scoot up alongside the vehicle
-Proximity sensors that sound a buzzer in the cab when an object is next
to the truck
- Audible warning devices that sound when the right turn signal is on
- Cameras to provide video feed into the vehicle of a wide angle view of
the outside environment
- Noisemakers, bells, and whistles for bicycles and cyclists



Women cyclists might want to have a mirror to help them put on their
make-up while riding.

On Feb 3, 8:43*am, SMS wrote:
Roger Zoul wrote:
"landotter" wrote in message news:gm1pt7
Don't you have ears? Use 'em. Experienced cyclists can tell what cars are
doing behind them by listening.

Nonsense. *I have been in plenty of situations where I could not even hear a
car coming up behind me.

It's amazing what crap people write in the internet when they don't have to
be accountable for any of it.

It's not just that, it's what they write when they have no idea of what
they're talking about! The attitude about mirrors seems to be a
knee-jerk reaction against them, even when they've never used them.

Step off yoursoap box of asinine assumptions before your ego blows out
your sinuses. Some of us have used every single commercially available
bike mirror and found them a terrible panacea for the thing called the
neck and ears. Most of them are built like **** as well. I broke six
Cat-Eyes or so before I came to the conclusion that mirrors are much
like Brooks saddles--a distraction.

What are they good for? Perhaps practicing pacelines--which in itself
is idiotic activity--drafting is really a fancy name for tailgating,
no? Also good for folks with spinal injuries who can't turn their
necks easily.

On Feb 3, 10:00*am, landotter wrote:

Some of us have used every single commercially available
bike mirror and found them a terrible panacea for the thing called the
neck and ears. Most of them are built like **** as well. I broke six
Cat-Eyes or so before I came to the conclusion that mirrors are much
like Brooks saddles--a distraction.

I agree that almost all are very poorly built. That's what led me to
build my own. It's not hard to improve greatly on commercial models,
especially if you're making them to fit only your own glasses.

What are they good for? Perhaps practicing pacelines--which in itself
is idiotic activity--drafting is really a fancy name for tailgating,
no? Also good for folks with spinal injuries who can't turn their
necks easily.

It's not only spinal injuries that hamper turning one's head like an
owl. Recumbent riders have problems because of their bike geometry,
and many people over 60 have problems due to fairly normal cervical
disk degeneration.

And as mentioned, I've found mirrors to have value even though I can
turn my head reasonably well. They allow a quick, general assessment
of rearward traffic which I find useful for judging gaps prior to left
turns. They also allow keeping tabs on fellow riders.

But the incidents that first tempted me to use a mirror involved
passing cars. Yes, I can usually hear upcoming cars (assuming the
wind isn't too strong), but I realized that I couldn't tell if I was
being passed by one car or two, or how closely I was being passed.
And when riding our pothole minefields, I found it very handy to know
whether a passing car was moving clear to the next lane or not. I can
easily tell these things with an eyeglass mirror.

I have no problem at all with people who say they don't need them. I
have no problem with people who say they've tried them but don't like
them, or can't get the hang of them. But I think the "oh ****"
vitriol they attract is pretty weird!

- Frank Krygowski

On Feb 3, 12:44*am, wrote:
Frank Krygowski wrote:
In an ordinary, full-sized mirror (like, say, a dressing room
mirror) depth perception works exactly as it does with no mirror.
At close range (up to, say, 20 feet) depth is judged partially by
parallax (the difference in image perceived by your left and right
eye) and partially by perspective (the reduction in image size at
greater distances). *It doesn't matter if the image you're seeing
is in a mirror or not...

*We've been here many times on wreck.bike in the past. *Your
assessment is entirely wrong and has been tested often.

It's been tested countless times. *I can test it now sitting in my
living room. *I can tell that the computer screen is closer than my
shoe, which is closer than the candlestick, which is closer than the
fireplace... and the parallax effect is obvious. *You can't see
those sorts of things?
...
No head movement was needed for those judgments above.

I doubt it, knowing the history of this flawed belief.

Sorry, you're wrong, at least for a certain range of distances.
There's an old parlor trick that involves having a person try (and
fail) to touch an object close to them with one of their eyes
closed. *I just replicated it by failing to touch the corner of this
new computer, because one of my eyes was closed. *Readers - or
contentious posters - can try it themselves.

As long as the distance is such that the cross-eyed angle is steep,
binocular focus helps, but assessing how far away things are that are
out of reach does not work. *Persons with only one functioning eye can
drive cars and get around without seeing-eye dogs well. *I've known a
few war related cases.

Yes, I've had several friends with only one functioning eye. That
merely demonstrates that binocular vision is not the _only_ method of
judging distance, which I already made clear. Similarly, my color-
blind friends have other ways of telling whether a traffic light is
red or green; that fact doesn't prove that color vision is not
effective!

Binocular vision works better at close range, and diminishes with
distance. The trigonometry is obvious. But the effect does not go to
zero beyond arm's reach. There's an outdoor stair rail about eight
feet from my eyes. Gazing at the snow and trees 20 feet beyond it
(yes, with my head motionless), I can easily see the double image of
the stair rail in the foreground. That's all the brain needs to know
the rail is closer, and to judge approximate distance.

Have you never seen a ViewMaster? Did you not understand how it
worked?


*http://www.vision3d.com/stereo.html
*http://en.wikipedia.org/wiki/Depth_perception
*http://health.howstuffworks.com/eye10.htm

There you see it again. *The myth is perpetuated by people who did no
research on the issue. *The Wiki article reiterates the folklore.

I think it's time for you to post references for your claims, rather
than just claim my references must be wrong.

Keep in mind, I've never said binocular vision is the only means of
judging distance, or relative distance; and I've said from the
beginning that its capability diminishes with distance. But your
notion seems to be that it doesn't work at all beyond three feet.
Tell us who has published confirmation of that.

- Frank Krygowski

Frank Krygowski wrote:

I have no problem at all with people who say they don't need them. I
have no problem with people who say they've tried them but don't like
them, or can't get the hang of them. But I think the "oh ****"
vitriol they attract is pretty weird!

I like mirrors, generally.

I prefer glasses mounted, as I usually dedicate a pair of glasses to
cycling and don't always wear a helmet.

I agree that most mirrors are pretty badly designed. I've used the
plastic ball socket ones, which are light and cheap, but develop slop
quickly and are really fussy to mount.

I find a mirror to be mostly useful in urban riding. I frequently shift
my line to avoid obstacles and find a mirror check is faster than a head
check. I just check to make sure there's sufficient room to weave out a
little. If in doubt, I don't. I haven't found my ears to be completely
reliable in noisy urban settings.

The visual obstruction is a bit distracting, but being in the upper
left, it usually doesn't mask hazards.

I do rely on a mirror completely when wearing one, I don't head check
for redundancy, even when crossing lanes. I always head check when
driving, but I don't have blind spots with a cycling mirror when I
rotate my head slightly.

:
: I have no problem at all with people who say they don't need them. I
: have no problem with people who say they've tried them but don't like
: them, or can't get the hang of them. But I think the "oh ****"
: vitriol they attract is pretty weird!
:
: - Frank Krygowski

That's my position, too. I don't care if people use or do not use mirrors. I
won't say that makes better or worse than other people. Hell, it doesn't
affect me if you use a mirror--or don't. Why the vitriol on this subject?
It's just a personal preference.

BTW: The "Take a Look" mirror is well-made. It's the best mirror I've seen.

Pat in TX

Tom Keats wrote:
In article ,
" writes:


The way you say that, I must assume your roads are not used by riders
like me although I am sure I have ridden on every kind of road you can
imagine. You paint a picture of imaginary roads used by murdering
motorists. That doesn't wash!


Try riding them on a weekday with 5 semi truck trains going by at 65 MPH
and you might get knocked off of your high and mighty attitude, for good.
There is a damn good reason I ride wrong side on certain sections of
road. Get over yourself, you have been lucky. If you don't think it
washes, just ride Hammonton/Smartsville road between Linda and
Smartsville on a weekday and see if you survive.


Who is forcing you to ride on this dangerous road?



It is the **ONLY** road that will get me to the mountains!!