Does lens coating effect chromatic aberration?
Prognathous
not change the dispersion qualities of a lens, it only reduces
aberrations such as glaring and flare and artifacts such as ghost
images.
Is this true?
TIA,
Prog.
Richard Ullakko
anytime the refraction index changes, thus making the lens much more
efficient.
Cheers
Sam Goldwasser
> According to everything I ever read on this subject, lens coating does
> not change the dispersion qualities of a lens, it only reduces
> aberrations such as glaring and flare and artifacts such as ghost
> images.
Dispersion is a bulk proper of the glass(es). Lens coatings only affect
the reflection at surfaces.
--- sam | Sci.Electronics.Repair FAQ Home Page: http://www.repairfaq.org/
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TP.
Your answer was factually correct but you didn't answer the question
that was asked.
The answer to the original question is "No". Lens coating is of great
benefit in many other ways, but it makes not one iota of difference to
chromatic aberration. Residual chromatic aberration is caused by poor
design and/or poor manufacture through ineptitude or penny pinching.
Bruce Murphy
> "Richard Ullakko" <ul...@nwlink.com> wrote:
>
> >It reduces the reflections that occur at any interface that is air-glass,
> >anytime the refraction index changes, thus making the lens much more
> >efficient.
>
>
> Your answer was factually correct but you didn't answer the question
> that was asked.
> The answer to the original question is "No". Lens coating is of great
> benefit in many other ways, but it makes not one iota of difference to
It makes no significant difference, but unless the coating material is
dispersionless, it /will/ make at least one, maybe two, iotas of
difference.
> chromatic aberration. Residual chromatic aberration is caused by poor
> design and/or poor manufacture through ineptitude or penny pinching.
Or originally through lack of materials capable of avoiding it in things
like extreme zooms.
B>
Stephen M. Dunn
$According to everything I ever read on this subject, lens coating does
$not change the dispersion qualities of a lens, it only reduces
$aberrations such as glaring and flare and artifacts such as ghost
$images.
Lens coating simply cuts down on reflections. Reflections can
cause glare and flare.
Aberrations such as curvilinear distortion, coma, spherical
aberration, and chromatic aberration are not cured by lens
coating.
--
Stephen M. Dunn <ste...@stevedunn.ca>
>>>----------------> http://www.stevedunn.ca/ <----------------<<<
------------------------------------------------------------------
Say hi to my cat -- http://www.stevedunn.ca/photos/toby/
TP.
>It makes no significant difference, but unless the coating material is
>dispersionless, it /will/ make at least one, maybe two, iotas of
>difference.
OK, let's split hairs. Look up the thickness of a lens coating and
its dispersive characteristics. Calculate the amount of dispersion.
If it is more than 0.1 iota, I will buy you a beer.
Repeating Decimal
progn...@hotmail.com wrote on 9/19/02 7:10 AM:
I have read a bunch of the replies.
If you shine a ray of light through a sequence of plane parallel plates of
glass, nout*sin (theta out) = nint*sin (theta in). That is, the media
between have no effect on the angle.
Bill
Bruce Murphy
Differing refractive indices with wavelength won't affect the exit
angle but they will cause lateral shifts to anything but normal rays
(You can convince yourself of this by looking at high n and low n
cases)
However, given that lenses are frequently not flat, the parallel plate
analogy is flawed. A coating of uniform thickness on a curved surface
is another lens, since it has a different radius of curvature.
B>
Repeating Decimal
pack...@rattus.net wrote on 9/19/02 7:08 PM:
> Differing refractive indices with wavelength won't affect the exit
> angle but they will cause lateral shifts to anything but normal rays
> (You can convince yourself of this by looking at high n and low n
> cases)
>
> However, given that lenses are frequently not flat, the parallel plate
> analogy is flawed. A coating of uniform thickness on a curved surface
> is another lens, since it has a different radius of curvature.
Assume a 25mm diameter sphere. Turn it down about a diameter to where you
have an almost cylinder, except for the spherical ends, 10 mm in diameter.
Now give it typical cheap AR coats on the ends of a quarter wavelength, say
of magnesium fluoride with n=1.38. Use a wavelength of 600 nm. If you could
remove those coatings intact, what would be the power of the equivalent
lens?
Now talk to me about the effect of curvature.
Bill
Bruce Murphy
You're not saying there *isn't* one, you're saying there isn't a
significantly large one to bother about. We were discussing a tiny
difference and your involved example pointing out that the difference
is very small doesn't actually add anything.
As far as lateral shifts go though, the additional curvature is less
significant than the fact that the lens isn't flat.
B>
Ian Stirling
Not always.
But, reducing chromatic aberration by adding bandpass filters is not
always appropriate.
--
http://inquisitor.i.am/ | mailto:inqui...@i.am | Ian Stirling.
---------------------------+-------------------------+--------------------------
"The theory of everything falls out trivially." -- Etherman, sci.physics kook.
brian
>
> If you shine a ray of light through a sequence of plane parallel plates of
> glass, nout*sin (theta out) = nint*sin (theta in). That is, the media
> between have no effect on the angle.
>
> Bill
Bill:
Its true that the angle of a single ray is unchanged after passing
through a sequence of parallel plates. However, if it enters the
sequence at an angle, then it will be displaced. If you place the
sequence of plates in a converging beam (eg. behind a lens) you will
thus introduce spherical aberration. In high aperture systems like
microscopes the effect becomes huge, and even an extremely thin plate
makes a big difference. That is why microscope objectives are
corrected with the coverglass in mind. If the converging beam is
tilted, then you also get astigmatism due to the parallel plates.
Prognathous
> Not always.
You mean that sometimes lens coating *does* introduce chromatic
aberration? and if so, how significant is it?
> But, reducing chromatic aberration by adding bandpass filters is not
> always appropriate.
I don't know about bandpass filters, but I would be very surprised to
discover that anyone tries to use lens coatings to "reducing chromatic
aberration", wouldn't you?
Prog.
Ian Stirling
>
> Ian Stirling <ro...@mauve.demon.co.uk> wrote in message news:<ameabt$lhu$1$8300de
> c...@news.demon.co.uk>...
>
>> Not always.
>
> You mean that sometimes lens coating *does* introduce chromatic
> aberration? and if so, how significant is it?
>
>> But, reducing chromatic aberration by adding bandpass filters is not
>> always appropriate.
>
> I don't know about bandpass filters, but I would be very surprised to
> discover that anyone tries to use lens coatings to "reducing chromatic
> aberration", wouldn't you?
If you coat a narrow-band filter onto a lens, you will greatly reduce
it's chromatic aberration.
--
http://inquisitor.i.am/ | mailto:inqui...@i.am | Ian Stirling.
---------------------------+-------------------------+--------------------------
"I am the Emperor, and I want dumplings." - Austrian Emperor, Ferdinand I.
Mike Tyner
"Ian Stirling" <ro...@mauve.demon.co.uk> wrote
> If you coat a narrow-band filter onto a lens, you will greatly reduce
> it's chromatic aberration.
That's true. Chromatic aberration is meaningless for a single wavelength. But
now the lenses are blue or yellow or red.
AR would be interesting on a mirror finish.
-MT
Paul Richards
band-pass filter) as
truly reducing the chromatic aberration. You might as well say any lens has no
chromatic aberration when used at a single wavelength.
BTW, it is "its chromatic aberration", not "it's chromatic aberration".
Prognathous
will never induce it.
Anyone thinks otherwise?
Prog.
Bruce Murphy
Yes, see the start of the thread. Of course whether you consider the amount
significant is another matter. :)
B>
Mike Tyner
Chromatic dispersion arises from the fact that blue light is bent slightly more
than red by most materials. Consequently blue light takes a slightly different
path through the lens than red does. A/R coatings can only affect reflections,
not the primary rays passing through the lens.
-MT
"Prognathous" <progn...@hotmail.com> wrote in message
news:e94173c3.02092...@posting.google.com...
Rudy Garcia
"Mike Tyner" <mty...@mindspring.com> wrote:
> I can't see any way for A/R coating to reduce chromatic.
>
> Chromatic dispersion arises from the fact that blue light is bent slightly
> more
> than red by most materials. Consequently blue light takes a slightly
> different
> path through the lens than red does. A/R coatings can only affect
> reflections,
> not the primary rays passing through the lens.
>
> -MT
Theoretically speaking, the AR coatings have a refractive index and are
curved with a radius very close (identical?) to the radius of the
underlying lens element. The AR coating's refractive index will also
vary with the wavelength of the impinging light (ie. the will have a
computable Abbe number). Thus, the AR coatings can, in principle,
affect the resultant chromatic aberration.
Does the lens designer take the AR coating effect into the design?
Probably not.
Is the contribution to the lens' chromatic aberration from the AR
coating discernible from the contribution of the different elements in
the prescription?
Probably not.
--
Rudy Garcia
Mike Tyner
is zero. How thick do you think these coatings are?
-MT
"Rudy Garcia" <ru...@jps.net.invalid> wrote in message
news:rudyg-CAE9BD....@nnrp03.earthlink.net...
D. Glenn Arthur Jr.
Mike Tyner <mty...@mindspring.com> wrote:
>Chromatic dispersion increases with thickness, and vanish to zero when
>thickness is zero. How thick do you think these coatings are?
Actually, we know how thin these coatings are: 1/4 of the
wavelength that a particular coating is targeted at. For a
single-coated lens with only the front of the front element
coated, that'd be some frequency middle-ish in the visible
spectrum. For lenses with with multiple coated surfaces and
multi-layer coatings (uh, that's pretty much any lens made in
the past few decades, right?) my understanding is that they
make each coated surface act on a different frequency so as
to spread the benefit of the coatings around the spectrum a
bit, which is why the reflections you see looking into a
complex lens are different colours.
So that means between 1000 and 2000 Angstroms, or between
0.00001 cm and 0.00002 cm.
--
D. Glenn Arthur Jr./The Human Vibrator, dgl...@radix.net
Due to hand/wrist problems my newsreading time varies so I may miss followups.
"Being a _man_ means knowing that one has a choice not to act like a 'man'."
<a href="http://www.radix.net/~dglenn/">Glenn's page</a>
Bruce Murphy
> Chromatic dispersion increases with thickness, and vanish to zero when thickness
> is zero. How thick do you think these coatings are?
Not zero :)
B>
Prognathous
Of course whether you consider the amount significant is another
matter. :)
Do *you* consider it significant or even visible at all? it seems
fairly theoretical to me.
Prog.
Rudy Garcia
"Mike Tyner" <mty...@mindspring.com> wrote:
> Chromatic dispersion increases with thickness, and vanish to zero when
> thickness
> is zero. How thick do you think these coatings are?
>
> -MT
Usually a quarter wave thick. That is why I said their contribution to
chromatic aberrations are not discernible.
--
Rudy Garcia
Mike Tyner
-MT
"Bruce Murphy" <pack...@rattus.net> wrote in message
news:m2vg4yj...@fuscipes.rattus.net...
Bruce Murphy
> Not zero, but not measurable.
I disagree, they're only not measurable, or at least not measured on
extraordinarily bad lenses such as those by Quantaray, Sigma, or
Canon.
B>
sibirer
"TP." <t...@nomailthankyou.com> wrote in message
news:9npjou4p56pagglmj...@4ax.com...
OK , design a lens system that can be fabricated to cover -20D to + 14 D
with up to 10D of toric curves while allowing up to +3D of power for near
reading. Now take into consideration that the eye can move and will rotate
off axis at least 25 to 30 degrees while the lens is fixed. Oh, let's also
add that you have no control over how far from the eye the lens is placed or
what angle horizontally or vertically it will be sitting at. Finally, it
must be affordable by at least most citizens of the industrialized world.
When a design is adaptable enough to work as a spectacle lens. There will be
tradeoffs in performance. The fact that the trade offs are as small as they
are indicates extremely advanced designs from highly educated and thoughtful
people with large bankrolls behind them.
Carl
Nuuccha
certainly reduce the observed chromatic aberration
Neuman - Ruether
<nuu...@mail.ru> wrote:
>In case the coating cuts a narrow band from input spectrum, it will
>certainly reduce the observed chromatic aberration
>Mike Tyner wrote:
>> Not zero, but not measurable.
I think MT's answer is correct...
At least on any "normal" lens, if the
coating filtered a color strongly
enough to affect observed CA, it would
be unacceptable for use as a lens for
general photography...
David Ruether
rp...@cornell.edu
http://www.ferrario.com/ruether
Hey, check out www.visitithaca.com too...!
Don Stauffer
use narrow bandpass filters, and did not put a tight spec on chromatic
aberration of lens.
But for color photography, you cannot narrow spectrum that much with
coatings, or the result would NOT be a color camera.
Long time ago (mid eighteenth century) films were not very red
sensitive, so lenses in those days were not as well corrected for
chromatic aberration. Not true today, of course.
--
Don Stauffer in Minnesota
stau...@usfamily.net
webpage- http://www.usfamily.net/web/stauffer
Jim Klein
have chromatic aberrations and in this way you could say coatings
help. It is just that they don't really help the non-multiple
reflection chromatic aberration to any great extent.
Jim Klein
Neuman - Ruether
Nice in theory, but the reflections would not be focused,
removing their chromatic aberration problem - but even that
is not relevant, since even if the reflected CA problem
were imaged on the film, it would be at a level too low to
register visibly on the film...;-) In other words, forget
coatings as a way to correct CA (unless, of course, they
are applied thick, with controlled and varying thicknes,
and are designed to modify the lens element curvature in
a way that is able to correct CA...;-).
Watch King
with a "reply" function that showed up in my usenet posting vehicle
for this thread.
Okay so define coating please. Tamron uses one surface of a glass lens
as the surface to "coat" with a very thick (0.1mm-1.0mm thickness)
asherical "plastic" material whose sole purpose is to correct for a
variety of distortions in their zoom lenses and some of these are
chromatic distortions. Of course both surfaces of this new
multi-material lens are then coated with anti-reflection materials to
reduce material to air reflections, but was the original plastic
molded onto the glass lens a coating or not.
Also to correct the statement about extremely narrow bandbass coatings
making a lens unusable for photography, it can in fact make the lens
more useful for photography. When an extremely narrow bandpass coating
or multicoating is applied to a rather plain glass lens so that only
the H Alpha range of visual spectrum will pass through a lens, details
about the surface of the sun become visible which would not normally
be visible to either the eye or film. The surface of the sun is quite
fascinating when viewed through lenses made of a single piece of
glass, specifially not color corrected, but coated so there is total
rejection of all visible light except for .1 nanometer's worth of the
H Alpha visible spectrum.
Normally I only lurk here unless I have questions, but being an
amateur astrophotgrapher I use very narrow band filters (produced by
coatings on glass)all the time for night sky light pollution
rejection, narrow band viewing of barely luminous objects in deep
space and solar viewing. WK
We don't get enough sand in our glass
rp...@cornell.edu (Neuman - Ruether) wrote in message news:<3deb8b5e...@newsstand.cit.cornell.edu>...
Repeating Decimal
watchki...@lycos.com wrote on 11/30/02 7:29 PM:
> Also to correct the statement about extremely narrow bandbass coatings
> making a lens unusable for photography, it can in fact make the lens
> more useful for photography. When an extremely narrow bandpass coating
> or multicoating is applied to a rather plain glass lens so that only
> the H Alpha range of visual spectrum will pass through a lens, details
> about the surface of the sun become visible which would not normally
> be visible to either the eye or film. The surface of the sun is quite
> fascinating when viewed through lenses made of a single piece of
> glass, specifially not color corrected, but coated so there is total
> rejection of all visible light except for .1 nanometer's worth of the
> H Alpha visible spectrum.
>
With all the posting on lens coating, I thought that it is time to point out
that THIN-FILM coating has virtually no effect on the refraction or any
lens. The coating described above should be considered to be an additional
refractive element rather that a thin-film coating used for anti-reflection.
If you at Snell's law, the direction a ray takes on the outside of a lens is
determnined only by ratio of indexes between the outsid and the inside of
the lens. This assumes that the coating is indeed so thin that it cannot act
as an additional lens element. There may some physical optical effects such
as evanascent field, but I have a hard time thinking of an application where
that would be important.
Bill
Don Stauffer
is not what 99% of camera purchasers want, I believe.
--
Bob May
photography, the concept was for full color photography of something in real
time. Yes, filters like the Ha filter can be used for photographing stuff
but the intention is to filter the light to just something of interest, not
take a picture of a pretty girl on the beach.
Chromatic aberration is a problem with any refractive optics and this is a
large part of why astonomical imagers stopped trying to get bigger and
better lenses for astronomical usage. Part of its problem is that the
different glasses just don't match up for dispersion and have different
refraction. This makes errors as the light goes through as the different
colors of light get refracted different amounts.
--
Bob May
Global WARMING???
What I want to know is when I can start growing wheat in Greenland again!
David Littlewood
<watchki...@lycos.com> writes
>Hello all, just using this post to "reply" because it's the only one
>with a "reply" function that showed up in my usenet posting vehicle
>for this thread.
>
>Okay so define coating please. Tamron uses one surface of a glass lens
>as the surface to "coat" with a very thick (0.1mm-1.0mm thickness)
>asherical "plastic" material whose sole purpose is to correct for a
>variety of distortions in their zoom lenses and some of these are
>chromatic distortions. Of course both surfaces of this new
>multi-material lens are then coated with anti-reflection materials to
>reduce material to air reflections, but was the original plastic
>molded onto the glass lens a coating or not.
No, it is really an optical element, just one which is made in an
unusual manner.
>
>Also to correct the statement about extremely narrow bandbass coatings
>making a lens unusable for photography, it can in fact make the lens
>more useful for photography. When an extremely narrow bandpass coating
>or multicoating is applied to a rather plain glass lens so that only
>the H Alpha range of visual spectrum will pass through a lens, details
>about the surface of the sun become visible which would not normally
>be visible to either the eye or film. The surface of the sun is quite
>fascinating when viewed through lenses made of a single piece of
>glass, specifially not color corrected, but coated so there is total
>rejection of all visible light except for .1 nanometer's worth of the
>H Alpha visible spectrum.
Interesting. Not exactly photography, though; more like spectroscopy
with directional information :-)
>
>Normally I only lurk here unless I have questions, but being an
>amateur astrophotgrapher I use very narrow band filters (produced by
>coatings on glass)all the time for night sky light pollution
>rejection, narrow band viewing of barely luminous objects in deep
>space and solar viewing. WK
>
>We don't get enough sand in our glass
--
David Littlewood
David Littlewood
<bob...@nethere.com> writes
>Chromatic aberration is a problem with any refractive optics and this is a
>large part of why astonomical imagers stopped trying to get bigger and
>better lenses for astronomical usage. Part of its problem is that the
>different glasses just don't match up for dispersion and have different
>refraction. This makes errors as the light goes through as the different
>colors of light get refracted different amounts.
>
cause chromatic aberration; it is the method used to cure it.
--
David Littlewood
Watch King
> >as the surface to "coat" with a very thick (0.1mm-1.0mm thickness)
> >asherical "plastic" material whose sole purpose is to correct for a
> >variety of distortions in their zoom lenses and some of these are
> >chromatic distortions. Of course both surfaces of this new
> >multi-material lens are then coated with anti-reflection materials to
> >reduce material to air reflections, but was the original plastic
> >molded onto the glass lens a coating or not.
>
> No, it is really an optical element, just one which is made in an
> unusual manner.
<snip>Then why does Tamron say that they coat a glass element with a
thin layer of resin to creat an aspherical surface? When does a
coating stop being a coating?
> Interesting. Not exactly photography, though; more like spectroscopy
> with directional information :-)
> >
<snip>These look like photographs to me. They are called photographs
too. Most use H Alpha narrowband filters but a few use slightly
different rejection filters.
Don Stauffer
we'd make lenses with no chromatic.
--
Repeating Decimal
watchki...@lycos.com wrote on 12/2/02 6:24 AM:
> <snip>Then why does Tamron say that they coat a glass element with a
> thin layer of resin to creat an aspherical surface? When does a
> coating stop being a coating?
It is of course a matter of definition. I think of an *optical thin-film
coating* as a series of thin layers of optical material used to modify
transmission or reflection of light by means of interference.
Bill