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Science Forum Index » Optics Forum » flaws in eyeglasses - testing for? Best quality mfgr...
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 Posted: Sun May 04, 2008 8:39 am |
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Guest
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Does anyone know of a way to detect and document optical flaws in eye
glasses?
I am NOT referring to a mis-made lens that doesn't match the
prescription. Rather, I am trying to document flaws in the base
material or imperfections in the surfacing - much like you see in
cheap plastic toy magnifying lenses that have wavey, fuzzy, or
distorted patches.
Please pardon the long post, but this is not simple to explain.
Background:
I have a strong eyeglass prescription - and have for 30+ years.
-8.00 -1.25 x 40
-7.50 -2.25 x 83
with a +2.5 magnifier for presbiopia. (being over 40 has its
challenges!)
In the past, the new lenses I've received have always been fine - I
could see clearly from side to side, and up/down within the limits of
the lens and the progressive lens distance design.
However, with my most recent attempts I cannot get a pair in which
both lenses are of good optical quality. The first pair delivered were
badly flawed in both eyes. The optician said they "tested fine" on
their equipment, but agreed to remake the lenses because she had
experienced a similar failure herself.
The next pair the left eye is fine, but the right eye still has
wavey/fuzzy zones that limit me to small areas of clarity. If I turn
my head or move my eye slightly, and look through a different portion
of the lens, I cannot read print -on paper or on the computer screen.
Clarity is disrupted by several diagonal stripes of fuzzyness across
the field of view from upper left to lower right.
Since the clear spot on the right eye does not match the head position
for best vision on the left, I'm getting headaches from eye strain
when doing any close work.
Since the next optician generally only offers one free "remake," for
user preceived errors, they are delaying remaking the lens again.
(I've checked with other shops in the area, and this appears to be
standard policy).
Therefore, I am trying to construct a system for projecting light
through the lens and recording the resulting difraction/projection
pattern in hopes that this illustrate the imperfections and thus
substantiate my claims of a flawed lens. (Visually its obvious to me,
but I'm told by the optician that their testing tools showed no error
on either set of lenses.)
I have access to good photography equipment (digital), strobes, and a
laser pointer. I have thought it might be possible "paint" a time
lapse image of the laser light being passed through the lens onto
graph paper to detect any areas that are unevenly lit, (much as the
old science class wave tables showed the wave patterns on the paper
below.) However I lack the knowledge to figure out how to position and
move the laser to accurately map the lens.
Any suggestions are welcome!
PS - I've used this optical shop for years, the lenses are coming from
the lab they routinely use with good results.
In case anyone is familiar with lens manufacturers, these are
supposedly from Definity Progressive Lenses. www.definity.com
If I decide to bite the bullet and pay the $350+ remake fee myself, is
there another manufacturer anyone knows to be better/more reliable?
Thank you for your patience - this is making my life quite difficult
right now, and any help or thoughts are greatly appreciated. |
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| Posted: Sun May 04, 2008 10:05 am |
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Guest
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Look at each lens between crossed linear polarizer filters with a
light table backlight, you will see the opto-mech stress from the
mounting and most likely any bulk plastic issues, and you should be
able to photograph these patters with your digital camera and show the
optician. If you dont have any cross polarizers you should be able to
use the one's at the opticians shop, they have them for checking
stress polarization in glass lenses after heat treatement.
You can also get some polymer one's fairly cheap through edmund
optics.
If you suspect surface issues you can take the glasses off your head
and look at a reflection from a straight edged light source (like a
fluorescent light fixture in the ceiling or the top or edge of a
window in your house). Slowly rotate the reflection from the stright
edge across the outer and inner surface of the lens, when you see a
localized departure from a line or smooth curve this is a surface
defect in curvature.
I am making an assumption that these are polymer progressive lenses
from you note.
Progressive lenses will have surface irregularitities on either the
outer convex surface, or the inner concave surface or both.
Is this your first pair of progressive lenses? I know many people
that have tried them an hated them, many opticians say that it usually
take about 3 weeks to get used to them, if you like them at all.
Besides the excellent recommendations by AES you may also try
contacting the progressive lens company and try to get their R&D or
marketing dept to make you a "good" pair or to test them or to have
another one of their more experiened & qualified labs make them for
you.
I will say that you rx is probably fairly challenging, mine is about
1/2 of your power's and I had a very hard time getting some rx wrap
around sunglasses made into a nice looking frame. Once I got them
made about 6 months later in a baskeball game with my daughter she was
going for a rebound and gave me a good elbow on the way down and broke
the plastic hinge at the temple - I have been using a piece of wire
ever since.
Let us know what happens, and good luck.
Michael
www.oscintl.com |
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| AES... |
| Posted: Sun May 04, 2008 1:56 pm |
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In article <nter1494d1g13gbmcb1e9midtlvnm0bq2r at (no spam) 4ax.com>,
a_held at (no spam) hotmail.com wrote:
Quote:
If I decide to bite the bullet and pay the $350+ remake fee myself, is
there another manufacturer anyone knows to be better/more reliable?
Man, at that price, I absolutely would not give in without making a
large ruckus --- maybe a visit to Small Claims Court, maybe a letter
from an attorney, maybe have an independent lab check 'em out, maybe a
strong letter to local Chamber of Commerce, maybe some posts to local
consumer group websites --- or maybe an initial threat to do all of the
above, coupled with a compromise offer to pay an $35 "restocking fee"
for turning in the defective pair and getting a remade pair --- this fee
to be paid ***once a re-made pair that meet specs have been delivered to
you***.
What kind of garbage is this "deliver faulty product, refuse to correct
the defect" approach?!?!?! |
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| Helmut Wabnig... |
| Posted: Sun May 04, 2008 2:11 pm |
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On Sun, 04 May 2008 11:56:51 -0700, AES <siegman at (no spam) stanford.edu> wrote:
Quote: In article <nter1494d1g13gbmcb1e9midtlvnm0bq2r at (no spam) 4ax.com>,
a_held at (no spam) hotmail.com wrote:
If I decide to bite the bullet and pay the $350+ remake fee myself, is
there another manufacturer anyone knows to be better/more reliable?
Man, at that price, I absolutely would not give in without making a
large ruckus --- maybe a visit to Small Claims Court, maybe a letter
from an attorney, maybe have an independent lab check 'em out, maybe a
strong letter to local Chamber of Commerce, maybe some posts to local
consumer group websites --- or maybe an initial threat to do all of the
above, coupled with a compromise offer to pay an $35 "restocking fee"
for turning in the defective pair and getting a remade pair --- this fee
to be paid ***once a re-made pair that meet specs have been delivered to
you***.
What kind of garbage is this "deliver faulty product, refuse to correct
the defect" approach?!?!?!
But he has to produce proof that the lenses are faulty.
I wonder if a polarization test would reveal streaks in the glass?
w. |
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| Posted: Sun May 04, 2008 10:27 pm |
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Thanks to everyone for the excellent suggestions!
I will follow Michael's technical suggestions next week - I assume I
can use a couple photographic polarizing filters?
I have worn progressives for over six years, and have a pair with just
a weaker version of the same basic prescription that are without these
flaws. So I agree, there IS a learning curve for them - but that's
clearly not my problem here.
Again, thanks. (and AES - NOT TO Worry - I'm a tenacious SOB when it
comes to fair dealing - and if I can document a real problem, I
believe this vendor will come through-- but it's a process that
today's dialog may well help me get through faster.
Regards,
Art
On Sun, 4 May 2008 13:05:20 -0700 (PDT), mpate at (no spam) oscintl.com wrote:
Quote: Look at each lens between crossed linear polarizer filters with a
light table backlight, you will see the opto-mech stress from the
mounting and most likely any bulk plastic issues, and you should be
able to photograph these patters with your digital camera and show the
optician. If you dont have any cross polarizers you should be able to
use the one's at the opticians shop, they have them for checking
stress polarization in glass lenses after heat treatement.
You can also get some polymer one's fairly cheap through edmund
optics.
If you suspect surface issues you can take the glasses off your head
and look at a reflection from a straight edged light source (like a
fluorescent light fixture in the ceiling or the top or edge of a
window in your house). Slowly rotate the reflection from the stright
edge across the outer and inner surface of the lens, when you see a
localized departure from a line or smooth curve this is a surface
defect in curvature.
I am making an assumption that these are polymer progressive lenses
from you note.
Progressive lenses will have surface irregularitities on either the
outer convex surface, or the inner concave surface or both.
Is this your first pair of progressive lenses? I know many people
that have tried them an hated them, many opticians say that it usually
take about 3 weeks to get used to them, if you like them at all.
Besides the excellent recommendations by AES you may also try
contacting the progressive lens company and try to get their R&D or
marketing dept to make you a "good" pair or to test them or to have
another one of their more experiened & qualified labs make them for
you.
I will say that you rx is probably fairly challenging, mine is about
1/2 of your power's and I had a very hard time getting some rx wrap
around sunglasses made into a nice looking frame. Once I got them
made about 6 months later in a baskeball game with my daughter she was
going for a rebound and gave me a good elbow on the way down and broke
the plastic hinge at the temple - I have been using a piece of wire
ever since.
Let us know what happens, and good luck.
Michael
www.oscintl.com
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| Salmon Egg... |
| Posted: Mon May 05, 2008 1:06 am |
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Guest
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In article <nter1494d1g13gbmcb1e9midtlvnm0bq2r at (no spam) 4ax.com>,
a_held at (no spam) hotmail.com wrote:
Quote: Does anyone know of a way to detect and document optical flaws in eye
glasses?
As you said, your post was long and I did not read it all.
I would guess that your best bet is a schlieren arrangement. See
Wikipedia.
To summarize, A point source of light or laser is focused to a spot. A
stop at that spot prevents light from getting past that spot. If you
back toward the source (presuming the source is the only light source,
you see nothing because the stop prevents any light from reaching the
eye. Remember, when using an intense source, BE EYE SAFE.
If you place the test sample in the path of the light, any nonuniformity
in the medium will scatter light in such a way as to miss the stop. Now
you can look back at the object and see what part is doing the
scattering.
If the object being tested is a lens, you have to figure where and what
kind of stop to use and compensate for the test objects refraction.
The Foucault knife test can be considered to be a schlieren test.
Bill |
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| Joe... |
| Posted: Mon May 05, 2008 8:28 am |
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Guest
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If your photo setup uses autofocusing lenses, the polarizers will be
circularly-polarized, and won't be what was suggested. Polarizers for
the "old fashioned" manual focus lenses are what you want (or a couple
of lenses from polarizing sunglasses will do).
Joe
On Sun, 04 May 2008 21:27:32 -0600, a_held at (no spam) hotmail.com wrote:
Quote: Thanks to everyone for the excellent suggestions!
I will follow Michael's technical suggestions next week - I assume I
can use a couple photographic polarizing filters?
snip
Regards,
Art
On Sun, 4 May 2008 13:05:20 -0700 (PDT), mpate at (no spam) oscintl.com wrote:
Look at each lens between crossed linear polarizer filters with a
light table backlight, you will see the opto-mech stress from the
mounting and most likely any bulk plastic issues, and you should be
able to photograph these patters with your digital camera and show the
optician. If you dont have any cross polarizers you should be able to
use the one's at the opticians shop, they have them for checking
stress polarization in glass lenses after heat treatement.
You can also get some polymer one's fairly cheap through edmund
optics.
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| Posted: Mon May 05, 2008 10:19 pm |
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Guest
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You are 100% correct - they are CPL filters.
Thanks for saving me from THAT mistake.
I'll get some cheapies and give 'em a try.
On Mon, 05 May 2008 09:28:49 -0400, Joe <see_real_one at (no spam) sig.lin> wrote:
Quote: If your photo setup uses autofocusing lenses, the polarizers will be
circularly-polarized, and won't be what was suggested. Polarizers for
the "old fashioned" manual focus lenses are what you want (or a couple
of lenses from polarizing sunglasses will do).
Joe
On Sun, 04 May 2008 21:27:32 -0600, a_held at (no spam) hotmail.com wrote:
Thanks to everyone for the excellent suggestions!
I will follow Michael's technical suggestions next week - I assume I
can use a couple photographic polarizing filters?
snip
Regards,
Art
On Sun, 4 May 2008 13:05:20 -0700 (PDT), mpate at (no spam) oscintl.com wrote:
Look at each lens between crossed linear polarizer filters with a
light table backlight, you will see the opto-mech stress from the
mounting and most likely any bulk plastic issues, and you should be
able to photograph these patters with your digital camera and show the
optician. If you dont have any cross polarizers you should be able to
use the one's at the opticians shop, they have them for checking
stress polarization in glass lenses after heat treatement.
You can also get some polymer one's fairly cheap through edmund
optics.
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