Sensor dust Nikon D80

Jim Townsend <not.RemoveThis@real.address> wrote:
>But there are major differences between CRT screens and sensors. CRT
>screens have a charge of 20 to 40 thousand volts behind the glass.
>CMOS and CCD sensors only use 3 to 5 volts. I can't see much of a
>charge being built up.

It does not require thousands of volts to create an
attraction to dust. (And indeed, there is nothing like
any thousands of volts on the _front_ of a CRT screen!)

Consider that anti-static plastic (the pink stuff) was
"discovered" because polyplastic sample containers
required washing less often if the soap solution was
_not_ rinsed off! The soap acted as a water dispersant,
reducing the ability to retain a charge, and therefore
less dust attached to the surface. Not only was there
no thousands of volts, there wasn't even a few
millivolts!

>Not only that, but the surface of sensor itself is covered with an anti
>aliasing filter. This AA filter is coated with a thin layer of a clear
>conductive substance. (Indium tin oxide is commonly used on modern sensors).
>
>This conductive coating allows any electrical charge which may occur to bleed
>off before it can build up. In other words, the conductive coatings they
>use on the AA filter makes sure that a static charge can't occur.

Sure, now compare that to the example of polyplastic
contrainers, which collect dust and require washing
every few weeks because they become visually
unattractive when covered with dust, as opposed to
digital cameras which commonly go for many many months,
if not years, without a visible or measureable amount of
dust.

--
Floyd L. Davidson <http://www.apaflo.com/floyd_davidson>
Ukpeagvik (Barrow, Alaska) floyd.RemoveThis@apaflo.com
 >> Stay informed about: Sensor dust Nikon D80 

Chris Malcolm <cam DeleteThis @holyrood.ed.ac.uk> wrote:
>> Actually the difference is that the surface of a CRT
>> screen is well insulated while the terminals of a
>> battery are usually connected to conductors that drain
>> off and disperse any static charge instantly.
>
>It's obvious you don't understand the physics,

Yeah, right.

>because that example
>supports my point, not yours.

Wrong.

>Because unless the battery is shorted
>out,

That would have absolutely *no* effect on static charge.

>any circuit it is connected to will keep a potential difference
>between the postive and negative terminals even when it is switched
>on.

The difference between the terminals has nothing to do
with it. Dust will be attracted by an electrostatic
charge, not by a difference in voltage potential.

>Same goes for a naked unconnected battery -- a low voltage
>potential difference. Yet we do not see a dust collecting differential
>between the two terminals of a battery left out in the open air.

Static charge does not equate to the same thing as
voltage difference.

>>>What is more, operability
>>>at the low voltages at which camera sensors work implies a
>>>conductivity which would not permit the development of dust attracting
>>>static charges.
>
>> I don't follow that reasoning? There is no implication
>> of higher conductivity with low voltages.
>
>There is in the sense that some things unconductive enough to be
>considered insulators at low voltages are still conductive enough to
>leak off static charges, a fact that engineers often exploit in
>keeping static charges away from sensitive CMOS circuitry (a
>technology often employed in digital camera sensors, and almost
>always employed in the circuits connected to it).

So the glass used for the AA filter, or for lenses, is
not a good insulator????

You might want to look into time constants too. You'll
find that most static discharge circuits (wrist straps,
etc), have a 10MOhm or so resistor. That does prevent a
high voltage static buildup (which is what will damage
electronic components), but will also prevents a rapid
discharge (which might damage the human using the
device). Think about the time constants for dust
attraction and an open shutter on a DSLR...

>>>There could be a dust attracting static charge involved, but it could
>>>not be due to the low voltage electronic operation of the sensor. It
>
>> Why not?
>
>Check the physics of static attraction for the theory,

You probably should do that.

>or for a
>practical experiment check the differential dust collection between
>the termimals on a naked unconnected flashlight battery.

That does not constitute a practical experiment for
electrostatic adhesion.

>>>could be due to some kind of transparent protective coating. However,
>
>> The coating itself does nothing except perhaps act as a
>> very good insulator, which is one of the two
>> requirements for a static build up (the other being a
>> source of charge).
>
>In order to prevent the coating causing static build up problems, the
>engineers have arranged that it is not a good enough insulator to hold
>a static charge.

Actually these devices are indeed engineered to reduce
static build up as much as possible, and in relative
terms are only very slightly subject to static build up
as compared to many other objects where that is not
done. But by that token, a CRT screen can suffer
millions of times more dust in a week than would be
reasonable to have on the camera's sensor in several
months.

Which is to say that static build up has been reduced,
but it is not eliminated.

And I'll note that you've argued that that type of
engineering is unnecessary because the CCD does not
produce a static charge when operating... yet there it
is, to help eliminate the effects you say shouldn't be
there.

>>>As far as I know
>>>the camera sensor is protected by a glass screen, and that is what
>>>gets dirty and needs to be cleaned. I can't see why an optical glass
>>>screen should suffer any more from static problems than do your camera
>>>lenses.
>
>> The camera lenses don't have a source of charge, other
>> than interaction with dry air. And indeed, that is
>> certainly enough to cause them to attract dust if the
>> air is dry.
>
>That's not how it works -- the dust that glass attracts in dry air is
>charged dust. The charge (to begin with) is on the dust, not the
>glass. Unless you deliberately charge the glass by rubbing it with an
>appropriate cloth, and it happens not to be semi-conductive (which
>modern optical coated lenses often are on purpose) Which doesn't
>happen on the digital sensor.

If you pass dry air (with or without dust in it) over a
glass surface (a high quality insulator) the glass
surface will in fact become charged. And it will in
fact then collect dust if it exists, which will be
attracted by, and adhere to it because of, the static
charge.

(Incidentally, no externally supplied voltage is needed.)

>>>What is more, I note that some DSLR makers use various sensor
>>>vibration cleaning methods which they claim help to keep their sensors
>>>dust free. These would not operate in the presence of electrical
>>>static attraction.
>
>> That would be correct. The sensor is not energized when
>> the cleaning mechanism of operating.
>
>Energising the sensor does not involve voltages high enough to attract
>dust.

Wrong. *Any* amount of static charge will attract dust.
Any any amount of voltage can be used to generate a
static charge, plus as noted above, an external source
is not even necessary (though it will greatly increase the
static charge that can be generated).

>>>Nor would the special brushes that use static
>>>charged bristles to attract the dust, since they would transfer charge
>>>to the sensor and make things worse.
>
>> Hmmm... I'm not sure that is true or false. Might be!
>> Interesting thought.
>
>Look up induction and transfer of static charge. It can't be avoided
>if you touch an uncharged perfect insulator with a charged one.

Induction???

But... that doesn't answer my point. What if it is
true that the brush transfers charge to the sensor? So
what? Is the brush a negative or a positive charge? And
what if the charge is transfered *to* the brush?

And what about the dust?

If the brush transfers just the right amount of charge,
the dust might just *all* *fall* *off*!

>> But regardless, the point is to
>> clean the sensor when it is *not* charged.
>
>Which will charge it up as every engineer knows unless special
>precautions have been taken to arrange a charge leakage path in either
>the surface or the cleaning material.

There almost certainly *is* a leakage path. And in some
cases added leakage is provided by the method used for
cleaning.

>You persist in thinking that the operating voltages of a digital
>camera sensor are enough to generate dust attractive static
>charges.

Because they are. The typical "contact potential"
between a surface and a particle is less that 1 volt.
It may be true that Laser printers use 500 volts to
generate a charge for electrostatic adhesion, but it is
also true that 10 volts in a camera, producing only
1/50th as much static charge, could still be a total
disaster!

>That's very definitely false,

Cite?

>although a lot of photographers
>who dozed during their school physics lessons do obviously believe that
>strongly enough to include the claim in educational materials they

Do you have any experience with electronics, or
electrostatics?

>>>But these are just educated guesses on my part, and I could easily be
>>>wrong. Do you have any good sources of information on this? I note for
>>>example that Wikipedia contains more superstition than science on this
>>>topic.
>
>> I hadn't looked at Wikipedia before. I found this
>> article, and thought it was pretty good, though it only
>> has two references and the first one is of questionable
>> value.
>
>> http://en.wikipedia.org/wiki/Dust_reduction_system
>
>> Where is the superstition you saw?
>
>It mentions dust adhering to the sensor through electrostatic charges,

I see no reason to claim that is a supersition.

>a phenomemon (so it claims) that can also be observed on LCD and CRT
>screens.

I see no reason to claim that is a supersition.

>That, as I have already explained, is a common superstition
>amongst photographers without a basic physics education.

As you have already misstated.

--
Floyd L. Davidson <http://www.apaflo.com/floyd_davidson>
Ukpeagvik (Barrow, Alaska) floyd DeleteThis @apaflo.com
 >> Stay informed about: Sensor dust Nikon D80 

Floyd L. Davidson <floyd DeleteThis @apaflo.com> wrote:
> Chris Malcolm <cam DeleteThis @holyrood.ed.ac.uk> wrote:
>>Floyd L. Davidson <floyd DeleteThis @apaflo.com> wrote:
>>> Jim Townsend <not DeleteThis @real.address> wrote:
>>>>Tully wrote:
>>>>
>>>>>--but the digital sensor
>>>>> with its static charge situation makes me even more cautious.
>>>>
>>>>What static charge?
>>
>>> The sensor is a electronic device, and when energized
>>> has a very significant static charge, which attracts
>>> dust particles in the air close to it.
>>
>>Checking sources of information on the web about this I find that many
>>of them are misinformed and get the science wrong. I checked because
>>just on first principles this sounds improbable. The voltages involved
>>in dust attraction are very high voltage static charges, whereas those
>>involved in the operation of a digital camera sensor are very
>>low.

> It isn't just high voltage circuits that have static
> charge problems. A low voltage circuit that transfers
> static charge to a very well insulated (and thus low
> leakage) collector will allow the accumulation of
> significant charge.

That involves movement and mechanical work against the static
repulsion which has to be engineered in the devices which exploit it
and is unlikely to be found by accident in a digital camera

> Keep in mind that something as apparently benign as
> rubbing two pieces of paper together can generate such a
> charge...

The rubbing is doing the work. There is no rubbing in the operation of
a digital camera sensor.

> And that virtually any high quality insulator
> in a dry atmosphere will 1) accumulate a charge,

And since such charges are very damaging to the camera's digital
electronics, the engineers have arranged that there are no high qualiy
insulators inside the camera capable of doing that.

>>That's why you get dust attracted to the surface of a CRT screen,
>>but not to the terminal of a torch battery.

> Actually the difference is that the surface of a CRT
> screen is well insulated while the terminals of a
> battery are usually connected to conductors that drain
> off and disperse any static charge instantly.

It's obvious you don't understand the physics, because that example
supports my point, not yours. Because unless the battery is shorted
out, any circuit it is connected to will keep a potential difference
between the postive and negative terminals even when it is switched
on. Same goes for a naked unconnected battery -- a low voltage
potential difference. Yet we do not see a dust collecting differential
between the two terminals of a battery left out in the open air.

>>What is more, operability
>>at the low voltages at which camera sensors work implies a
>>conductivity which would not permit the development of dust attracting
>>static charges.

> I don't follow that reasoning? There is no implication
> of higher conductivity with low voltages.

There is in the sense that some things unconductive enough to be
considered insulators at low voltages are still conductive enough to
leak off static charges, a fact that engineers often exploit in
keeping static charges away from sensitive CMOS circuitry (a
technology often employed in digital camera sensors, and almost
always employed in the circuits connected to it).

>>There could be a dust attracting static charge involved, but it could
>>not be due to the low voltage electronic operation of the sensor. It

> Why not?

Check the physics of static attraction for the theory, or for a
practical experiment check the differential dust collection between
the termimals on a naked unconnected flashlight battery.

>>could be due to some kind of transparent protective coating. However,

> The coating itself does nothing except perhaps act as a
> very good insulator, which is one of the two
> requirements for a static build up (the other being a
> source of charge).

In order to prevent the coating causing static build up problems, the
engineers have arranged that it is not a good enough insulator to hold
a static charge.

>>As far as I know
>>the camera sensor is protected by a glass screen, and that is what
>>gets dirty and needs to be cleaned. I can't see why an optical glass
>>screen should suffer any more from static problems than do your camera
>>lenses.

> The camera lenses don't have a source of charge, other
> than interaction with dry air. And indeed, that is
> certainly enough to cause them to attract dust if the
> air is dry.

That's not how it works -- the dust that glass attracts in dry air is
charged dust. The charge (to begin with) is on the dust, not the
glass. Unless you deliberately charge the glass by rubbing it with an
appropriate cloth, and it happens not to be semi-conductive (which
modern optical coated lenses often are on purpose) Which doesn't
happen on the digital sensor.

>>What is more, I note that some DSLR makers use various sensor
>>vibration cleaning methods which they claim help to keep their sensors
>>dust free. These would not operate in the presence of electrical
>>static attraction.

> That would be correct. The sensor is not energized when
> the cleaning mechanism of operating.

Energising the sensor does not involve voltages high enough to attract
dust.

>>Nor would the special brushes that use static
>>charged bristles to attract the dust, since they would transfer charge
>>to the sensor and make things worse.

> Hmmm... I'm not sure that is true or false. Might be!
> Interesting thought.

Look up induction and transfer of static charge. It can't be avoided
if you touch an uncharged perfect insulator with a charged one.

> But regardless, the point is to
> clean the sensor when it is *not* charged.

Which will charge it up as every engineer knows unless special
precautions have been taken to arrange a charge leakage path in either
the surface or the cleaning material.

You persist in thinking that the operating voltages of a digital
camera sensor are enough to generate dust attractive static
charges. That's very definitely false, although a lot of photographers
who dozed during their school physics lessons do obviously believe that
strongly enough to include the claim in educational materials they

>>But these are just educated guesses on my part, and I could easily be
>>wrong. Do you have any good sources of information on this? I note for
>>example that Wikipedia contains more superstition than science on this
>>topic.

> I hadn't looked at Wikipedia before. I found this
> article, and thought it was pretty good, though it only
> has two references and the first one is of questionable
> value.

> http://en.wikipedia.org/wiki/Dust_reduction_system

> Where is the superstition you saw?

It mentions dust adhering to the sensor through electrostatic charges,
a phenomemon (so it claims) that can also be observed on LCD and CRT
screens. That, as I have already explained, is a common superstition
amongst photographers without a basic physics education.

--
Chris Malcolm cam DeleteThis @infirmatics.ed.ac.uk DoD #205
IPAB, Informatics, JCMB, King's Buildings, Edinburgh, EH9 3JZ, UK
[http://www.dai.ed.ac.uk/homes/cam/]
 >> Stay informed about: Sensor dust Nikon D80 

Chris Malcolm wrote:

> Check the physics of static attraction for the theory, or for a
> practical experiment check the differential dust collection between
> the termimals on a naked unconnected flashlight battery.

Would you mind amusing the class by trying to explain why you think
batteries and static charges have any practical relationship here?

/me opens a bag of microwave popcorn and waits for the inevitable
"well, umm.... they're both electrical stuff" reply.

> It mentions dust adhering to the sensor through electrostatic charges,
> a phenomemon (so it claims) that can also be observed on LCD and CRT
> screens. That, as I have already explained, is a common superstition
> amongst photographers without a basic physics education.

You, sir, are a retard. It's nothing *but* physics that lays waste to
all of your blubbering. Modern sensors operating on nothing *but*
static charges and how photons dislodge electrons with stored
potential, and as any 9th grade general science student can tell you
the laws of conservation of energy deem that potential a problem for
digital photographers no matter how dedicated engineers may be to
"bleeding off" said charges. In fact, the very words from the engineers
you're pretending to cite would give an intelligent being the clues
they need to come to a logical conclusion about how static electricity
affects dist inside a modern digital camera, and why it most certainly
*is* a problem.
 >> Stay informed about: Sensor dust Nikon D80 

Tully wrote:

> All of that is interesting, but really doesn't relate to the OP's
> question. To the extent that I opened this can of worms by mentioning
> static, I regret it.

You shouldn't regret it, the people who are bickering about static
charge not existing on sensors/filters are simply being obtuse and
displaying their general ignorance. Of *course* sensors build up static
charges. That's how they function... part of their design.

The problem here is that Usenet is infested with self proclaimed
"experts" who would rather make laughable attempts to convince others
they're right than expend even the rudimentary effort it would take to
actually educating themselves about something so obvious.

Here's the first free clue: CCD stands for "Charge Coupled Device".

There's variations of course, but virtually all modern image sensors in
digital still cameras are little more than a plate with a series of
tiny little capacitors on it, packed full of static charge, which
release electrons when light hits them. Static electricity is the very
tool they use to capture images for God's sake, and while every
precaution within reason is taken to make that static charge less of a
problem to the consumer it's still a problem. You can't ignore physics,
and the fact that electrical potential sets up magnetic fields which in
turn can even create new potentials. That's just the way life is folks,
welcome to reality.
 >> Stay informed about: Sensor dust Nikon D80 

Chris Malcolm <cam.DeleteThis@holyrood.ed.ac.uk> wrote:
>Floyd L. Davidson <floyd.DeleteThis@apaflo.com> wrote:
>> Jim Townsend <not.DeleteThis@real.address> wrote:
>
>>>But there are major differences between CRT screens and sensors. CRT
>>>screens have a charge of 20 to 40 thousand volts behind the glass.
>>>CMOS and CCD sensors only use 3 to 5 volts. I can't see much of a
>>>charge being built up.
>
>> It does not require thousands of volts to create an
>> attraction to dust. (And indeed, there is nothing like
>> any thousands of volts on the _front_ of a CRT screen!)
>
>Perhaps not always, and not if it has good anti-static treatment, but
>it's not hard to find at least hundreds of volts on the surface of a
>non-static-treated CRT screen in dry air. And it's not difficult to
>produce thousands of volts by rubbing a suitable plastic on the sleeve
>of a pullover.

Which of course can be done with the TV *unplugged* too.

>The simple test is whether you can produce any kind of
>spark. The tiniest spark, just a little snap which is hardly visible,
>requires nearly 400 volts at normal temperatures and pressures.

What does that test tell you though? It says *nothing*
about an power supply voltages in the equipment
attached! You can get that much voltage from sliding two
pieces of paper together, from pulling a 2 inch strip of
Skotch Tape off of a piece of paper, from walking across
a dry carpet, or from putting 100 high precision
resistors into a paper envelope.

Not one of those actions requires any hundreds or
thousands of volts from an external power supply to
generate a static charge than can arc and spark.

Blow up a balloon and rub it on you head, and it will
cling to a wall. Does that mean your head has thousands
of volts inside???

>You
>can generate well over a thousand volts by stroking a dry cat in dry
>air with dry hands.

Any there's *no* power supply required!

>Attracting dust through air to a charged surface requires a potential
>difference of at least hundreds of volts.

Chris, that is simply not true. It requires no external
voltage, and the "contact voltage" that actually causes
adhesion is less than 1 volt.

--
Floyd L. Davidson <http://www.apaflo.com/floyd_davidson>
Ukpeagvik (Barrow, Alaska) floyd.DeleteThis@apaflo.com
 >> Stay informed about: Sensor dust Nikon D80 

Chris Malcolm <cam.TakeThisOut@holyrood.ed.ac.uk> wrote:
>Floyd L. Davidson <floyd.TakeThisOut@apaflo.com> wrote:
>> Chris Malcolm <cam.TakeThisOut@holyrood.ed.ac.uk> wrote:
>
>>>> Actually the difference is that the surface of a CRT
>>>> screen is well insulated while the terminals of a
>>>> battery are usually connected to conductors that drain
>>>> off and disperse any static charge instantly.
>
>>>It's obvious you don't understand the physics,
>
>> Yeah, right.
>
>Right, as will become clear.
>
>>>Because unless the battery is shorted
>>>out,
>
>> That would have absolutely *no* effect on static charge.
>
>Try and follow the argument. I'm not claiming that it does.

You mentioned it just because the words sounded nice?
Therapeutic noise is a wonderful thing. But please leave
it out of this discussion, okay?

>>>any circuit it is connected to will keep a potential difference
>>>between the postive and negative terminals even when it is switched
>>>on.
>
>> The difference between the terminals has nothing to do
>> with it. Dust will be attracted by an electrostatic
>> charge, not by a difference in voltage potential.
>
>If the electrostatic charge is not sufficient to cause a potential
>difference of at least hundreds of volts it's not going to be able to
>attract a dust particle to it through air.

That is 1) untrue, and 2) beside the point anyway.

All that really matters is if a dust particle that lands
on the sensor will adhere to it or not. The "contact
potential" required for adhesion is less than 1 volt.

>>>Same goes for a naked unconnected battery -- a low voltage
>>>potential difference. Yet we do not see a dust collecting differential
>>>between the two terminals of a battery left out in the open air.
>
>> Static charge does not equate to the same thing as
>> voltage difference.
>
>No, but there is a minimum potential difference resulting from the
>charge necessary to attract dust through air.

The voltages used in the camera have *nothing* at all to
do with the amount of static charge. *NOTHING*.

>>>>>What is more, operability
>>>>>at the low voltages at which camera sensors work implies a
>>>>>conductivity which would not permit the development of dust attracting
>>>>>static charges.
>>>
>>>> I don't follow that reasoning? There is no implication
>>>> of higher conductivity with low voltages.
>>>
>>>There is in the sense that some things unconductive enough to be
>>>considered insulators at low voltages are still conductive enough to
>>>leak off static charges, a fact that engineers often exploit in
>>>keeping static charges away from sensitive CMOS circuitry (a
>>>technology often employed in digital camera sensors, and almost
>>>always employed in the circuits connected to it).
>
>> So the glass used for the AA filter, or for lenses, is
>> not a good insulator????
>
>Insulation is relative to voltage.

On very rare occasions that is true, but this is not one
of them. A high enough voltage can indeed break down
the insulation and ionize it.

That is not something that relates to this discussion.

>It's usually treated with something
>which will provide at least enough conduction to allow static charge
>to leak away. That can still be a good enough insulator at the
>operating voltages of a digital image sensor.

The AA filter does not have to be an insulator at all.
If it were a very good conductor it would not affect
operation of the sensor.

Which is to say, your discussion is totally irrelevant.

The point is simply that the material used to make AA
filters happens to be a very good insulator. It is in
fact treated in an attempt to reduce its quality as an
insulator. That is done because static charge, despite
what you claim, *is* significant.

>> You might want to look into time constants too. You'll
>> find that most static discharge circuits (wrist straps,
>> etc), have a 10MOhm or so resistor.
>
>I don't need to "find" that. I've spent years of my working life
>wearing those things.

It doesn't appear that you understand how they work,
given the amount of incorrect information you've stated
in this thread.

>> That does prevent a
>> high voltage static buildup (which is what will damage
>> electronic components), but will also prevents a rapid
>> discharge (which might damage the human using the
>> device). Think about the time constants for dust
>> attraction and an open shutter on a DSLR...
>
>Which is why you might need even more than hundreds of volts in order
>for static charge dust attraction to be problem on digital camera
>sensors

You can't make a logical connect with that claim. There
is no relationship. Those wrist straps are not there to
prevent dust accumulation.

The time constant, however, *is* significant.

>>>or for a
>>>practical experiment check the differential dust collection between
>>>the termimals on a naked unconnected flashlight battery.
>
>> That does not constitute a practical experiment for
>> electrostatic adhesion.
>
>Because a potential difference of several volts, which is all that is
>involved in the operation of a digital camera sensor, no matter with
>how much charge, is far too little to attract dust through air.

You aren't paying attention to detail. We don't really
care whether it attracts dust through the air. What we
care about is whether dust adheres to the surface once
it comes into contact.

Regardless, you still haven't understood that the
voltage of an operating circuit, or across a battery
terminal, does *not* relate to the amount of static
charge which can accumulate.

Or even apparently that it isn't the voltage on the
conductors that attracts dust, even at high voltages.

>But if I were to stand the battery on top of a metal plate charged by
>a Wimhurst machine it would attract dust, which shows that nothing in

Which show virtually *nothing* about the battery.

>the battery except its potential with respect to the dust is what
>normally stops it from attracting dust.

I'm impressed. But 40 some years ago I worked with a
Van de Graaf particle accelerator that could burn through
2x4's. So I'm not impressed much...

>> And I'll note that you've argued that that type of
>> engineering is unnecessary because the CCD does not
>> produce a static charge when operating... yet there it
>> is, to help eliminate the effects you say shouldn't be
>> there.
>
>You haven't been following the argument.

You are the one who isn't following what's being discussed!

>My claim was that contrary to
>your claim the operating voltages of digital camera sensors are not
>enough to cause dust attracting electrostatic charges. But that's not
>the only way a surface can acquire a static charge, as you yourself
>point out later in this post. Hence the need for static discharge
>measures, even though the operating voltages won't cause electrostatic
>dust attraction problems.

You still think the voltage of the operating circuit is
directly related to the amount of static charge. That
is not true.

But worse yet, you've *totally* missed the point of the
original discussion, which was not whether the dust is
*initially* attracted to the sensor by static voltage
from an operating sensor! (And you have the nerve to
tell me I haven't been following the argument!).

The original point was that it is difficult if not
impossible to clean dust off the sensor when using the
"bulb" setting to open the shutter for access to the
sensor, as opposed to the camera's mirror lockup option
for cleaning, which gives access without energizing the
sensor.

The significant point was that electrostatic adhesion is
going to cause dust on the sensor to remain on the
sensor if the CCD is energized.

As I've repeated pointed out, electrostatic adhesion is
a function of "contact potential", and is typically less
than 1 volt.

Your discussion of high voltages is irrelevant. High
operating voltages for circuits are *not* required for
electrostatic charge build up. High operating voltages
may well make it more difficult to avoid, but not having
a high enough voltage is not a guarantee of not having
an electrostatic charge.

You are the only one excited about attracting dust. The
discussion was about removing the dust from the sensor,
not how it got there to start with.

....

>The numbers matter. While what you say is theoretically true, you need
>a certain dryness of air and strength of "passing" in order to
>generate enough charge to attract dust through air. I think you'd find
>it rather difficult to subject your camera to such conditions

Pick up your camera and walk across the room. In many
places (though granted not everywhere in the damp
climate you live in) that will be all it takes to
generate a huge electrostatic charge for your camera!

That isn't difficult at all...

>I think our terminology may be too loose here. A static charge is
>simply one that isn't moving.

There is a huge difference between the charge in a
battery (or other typical "power supply") and an
electrostatic charge!

>The static charges in CCD sensors are
>for example too low to generate enough electrostatic attraction to
>pull dust through air

The "contact potential" is less than 1 volt, and I dare
say that CCD sensors operate at a higher voltage than
that.

>, and while static, are far from the minimum
>voltages ususally considered necessry to become considered as
>electrostatic charges capable of exerting significant electrostatic
>attraction.

One volt.

>Dust attracting electrostatic forces start somewhere with
>effective potential differences in the hundreds of volts.

Chris that's bullshit. Less than 1 volt...

>>>>>Nor would the special brushes that use static
>>>>>charged bristles to attract the dust, since they would transfer charge
>>>>>to the sensor and make things worse.
>>>
>>>> Hmmm... I'm not sure that is true or false. Might be!
>>>> Interesting thought.
>>>
>>>Look up induction and transfer of static charge. It can't be avoided
>>>if you touch an uncharged perfect insulator with a charged one.
>
>> Induction???
>
>I suspected you were the one who was a bit light on electrostatic
>physics! Look up electrostatic induction in Wikipedia. It's important
>and fundamental and quite a different animal from the electromagnetic
>induction which I suspect you're confusing it with.

If you mean "electrostatic induction", that is what you
have to say. If it is "important and fundamental and quite
a different animal" than what you said, you need to correct
yourself rather than insult someone who gently points out
your mistake.

But I guess this sort of thing is to be expected, given
that your main source of information is Wikipedea...

>> But... that doesn't answer my point. What if it is
>> true that the brush transfers charge to the sensor? So
>> what? Is the brush a negative or a positive charge? And
>> what if the charge is transfered *to* the brush?
>
>Due to the electrostatic induction which you've never heard of that's
>rather difficult to arrange

So you have a brush that, according to you, cannot be
charged???? Yet, darned if it isn't.

That's just more nonsense...

>> And what about the dust?
>
>> If the brush transfers just the right amount of charge,
>> the dust might just *all* *fall* *off*!
>
>You're technically correct,

You've mentioned several times now that I am technically
correct. You might just ponder for awhile the concept
that I continue to be technically correct again and
again.

>but the idea is very difficult to put into
>practice.

Actually it's fairly easy.

1) Use an conductive coating on the sensor, to make sure
static charges are dissipated.
2) De-energize the CCD, to avoid adding static charge.
3) Vibrate the sensor.

You may have noticed that 2 or 3 camera manufacturers
are doing essentially just that.

>There have been some static charge reducers which worked on
>that principle by emitting a cloud of charged ions which were selected
>by attraction as needed until attraction vanished because attractive
>charge had been neutralised, but they didn't always have the intended
>effect.

The problem is that various dust particles have
*different* contact voltages as well as polarities.
Hence no matter what the sensor's charge actually is, it
*will* be attractive to some dust.

>>>You persist in thinking that the operating voltages of a digital
>>>camera sensor are enough to generate dust attractive static
>>>charges.
>
>> Because they are. The typical "contact potential"
>> between a surface and a particle is less that 1 volt.
>> It may be true that Laser printers use 500 volts to
>> generate a charge for electrostatic adhesion, but it is
>> also true that 10 volts in a camera, producing only
>> 1/50th as much static charge, could still be a total
>> disaster!
>
>If that is indeed the case, then you ought to be able to describe to
>me the experiment I can do with flashlight batteries which will show
>ten volts attracting dust particles through air.

Open up any 5 volt power supply and look to see where
there is more dust.

>>>although a lot of photographers
>>>who dozed during their school physics lessons do obviously believe that
>>>strongly enough to include the claim in educational materials they
>
>> Do you have any experience with electronics, or
>> electrostatics?
>
>Both. I've built and repaired amplifiers, computers, and electrostatic
>loudspeakers. I've still got at least a thousand dollars worth of
>electronic test gear lying around the house. In the days before
>digital cameras I even built a digital camera using part of a ceramic
>mil-spec dynamic RAM chip with the lid off as the sensor. I was
>playing with this stuff in labs long before you could look up
>miseducated superstitions on the web.

You are a fairly experienced hobbyist; and you do sound
exactly like one too.

>> As you have already misstated.
>
>So you say. But you're the one who boggled at the elementary and
>fundamental concept of electrostatic induction

I questioned your error in terminology. You are the one
who seems to be boggled by what you find on Wikipedia.

--
Floyd L. Davidson <http://www.apaflo.com/floyd_davidson>
Ukpeagvik (Barrow, Alaska) floyd.TakeThisOut@apaflo.com
 >> Stay informed about: Sensor dust Nikon D80 

Chris Malcolm <cam DeleteThis @holyrood.ed.ac.uk> wrote:
>> You, sir, are a retard. It's nothing *but* physics that lays waste to
>> all of your blubbering. Modern sensors operating on nothing *but*
>> static charges and how photons dislodge electrons with stored
>> potential,
>
>There's a very important difference between the static charges in such
>things as CCD sensors and electrostatic charges of sufficient
>magnitude to attract dust through air, literally orders of magnitude.

You are right for once!

CCD's typically operate at about an order of magnitude
*higher* voltage than the contact voltage between a
typical dust partical and the charged surface it adheres
to.

--
Floyd L. Davidson <http://www.apaflo.com/floyd_davidson>
Ukpeagvik (Barrow, Alaska) floyd DeleteThis @apaflo.com
 >> Stay informed about: Sensor dust Nikon D80 

On Jan 11, 5:34 pm, Cyberiade.it Anonymous Remailer
<anonym....DeleteThis@remailer.cyberiade.it> wrote:
> Tully wrote:
> > All of that is interesting, but really doesn't relate to the OP's
> > question. To the extent that I opened this can of worms by mentioning
> > static, I regret it.
>
> You shouldn't regret it, the people who are bickering about static
> charge not existing on sensors/filters are simply being obtuse and
> displaying their general ignorance. Of *course* sensors build up static
> charges. That's how they function... part of their design.
>
> The problem here is that Usenet is infested with self proclaimed
> "experts" who would rather make laughable attempts to convince others
> they're right than expend even the rudimentary effort it would take to
> actually educating themselves about something so obvious.
>
> Here's the first free clue: CCD stands for "Charge Coupled Device".
>
> There's variations of course, but virtually all modern image sensors in
> digital still cameras are little more than a plate with a series of
> tiny little capacitors on it, packed full of static charge, which
> release electrons when light hits them. Static electricity is the very
> tool they use to capture images for God's sake, and while every
> precaution within reason is taken to make that static charge less of a
> problem to the consumer it's still a problem. You can't ignore physics,
> and the fact that electrical potential sets up magnetic fields which in
> turn can even create new potentials. That's just the way life is folks,
> welcome to reality.

My my, what a great understander of physics you are
 >> Stay informed about: Sensor dust Nikon D80 

Floyd L. Davidson <floyd.DeleteThis@apaflo.com> wrote:
> Jim Townsend <not.DeleteThis@real.address> wrote:

>>But there are major differences between CRT screens and sensors. CRT
>>screens have a charge of 20 to 40 thousand volts behind the glass.
>>CMOS and CCD sensors only use 3 to 5 volts. I can't see much of a
>>charge being built up.

> It does not require thousands of volts to create an
> attraction to dust. (And indeed, there is nothing like
> any thousands of volts on the _front_ of a CRT screen!)

Perhaps not always, and not if it has good anti-static treatment, but
it's not hard to find at least hundreds of volts on the surface of a
non-static-treated CRT screen in dry air. And it's not difficult to
produce thousands of volts by rubbing a suitable plastic on the sleeve
of a pullover. The simple test is whether you can produce any kind of
spark. The tiniest spark, just a little snap which is hardly visible,
requires nearly 400 volts at normal temperatures and pressures. You
can generate well over a thousand volts by stroking a dry cat in dry
air with dry hands.

Attracting dust through air to a charged surface requires a potential
difference of at least hundreds of volts.

--
Chris Malcolm cam.DeleteThis@infirmatics.ed.ac.uk DoD #205
IPAB, Informatics, JCMB, King's Buildings, Edinburgh, EH9 3JZ, UK
[http://www.dai.ed.ac.uk/homes/cam/]
 >> Stay informed about: Sensor dust Nikon D80 

Floyd L. Davidson <floyd DeleteThis @apaflo.com> wrote:
> Chris Malcolm <cam DeleteThis @holyrood.ed.ac.uk> wrote:

>>> Actually the difference is that the surface of a CRT
>>> screen is well insulated while the terminals of a
>>> battery are usually connected to conductors that drain
>>> off and disperse any static charge instantly.

>>It's obvious you don't understand the physics,

> Yeah, right.

Right, as will become clear.

>>Because unless the battery is shorted
>>out,

> That would have absolutely *no* effect on static charge.

Try and follow the argument. I'm not claiming that it does.

>>any circuit it is connected to will keep a potential difference
>>between the postive and negative terminals even when it is switched
>>on.

> The difference between the terminals has nothing to do
> with it. Dust will be attracted by an electrostatic
> charge, not by a difference in voltage potential.

If the electrostatic charge is not sufficient to cause a potential
difference of at least hundreds of volts it's not going to be able to
attract a dust particle to it through air.

>>Same goes for a naked unconnected battery -- a low voltage
>>potential difference. Yet we do not see a dust collecting differential
>>between the two terminals of a battery left out in the open air.

> Static charge does not equate to the same thing as
> voltage difference.

No, but there is a minimum potential difference resulting from the
charge necessary to attract dust through air.

>>>>What is more, operability
>>>>at the low voltages at which camera sensors work implies a
>>>>conductivity which would not permit the development of dust attracting
>>>>static charges.
>>
>>> I don't follow that reasoning? There is no implication
>>> of higher conductivity with low voltages.
>>
>>There is in the sense that some things unconductive enough to be
>>considered insulators at low voltages are still conductive enough to
>>leak off static charges, a fact that engineers often exploit in
>>keeping static charges away from sensitive CMOS circuitry (a
>>technology often employed in digital camera sensors, and almost
>>always employed in the circuits connected to it).

> So the glass used for the AA filter, or for lenses, is
> not a good insulator????

Insulation is relative to voltage. It's usually treated with something
which will provide at least enough conduction to allow static charge
to leak away. That can still be a good enough insulator at the
operating voltages of a digital image sensor.

> You might want to look into time constants too. You'll
> find that most static discharge circuits (wrist straps,
> etc), have a 10MOhm or so resistor.

I don't need to "find" that. I've spent years of my working life
wearing those things.

> That does prevent a
> high voltage static buildup (which is what will damage
> electronic components), but will also prevents a rapid
> discharge (which might damage the human using the
> device). Think about the time constants for dust
> attraction and an open shutter on a DSLR...

Which is why you might need even more than hundreds of volts in order
for static charge dust attraction to be problem on digital camera
sensors

>>>>There could be a dust attracting static charge involved, but it could
>>>>not be due to the low voltage electronic operation of the sensor. It

>>> Why not?

>>Check the physics of static attraction for the theory,

> You probably should do that.

I will if you tell me something I don't know because you'll probably
have got it wrong

>>or for a
>>practical experiment check the differential dust collection between
>>the termimals on a naked unconnected flashlight battery.

> That does not constitute a practical experiment for
> electrostatic adhesion.

Because a potential difference of several volts, which is all that is
involved in the operation of a digital camera sensor, no matter with
how much charge, is far too little to attract dust through air.

But if I were to stand the battery on top of a metal plate charged by
a Wimhurst machine it would attract dust, which shows that nothing in
the battery except its potential with respect to the dust is what
normally stops it from attracting dust.

>>>>could be due to some kind of transparent protective coating. However,
>>
>>> The coating itself does nothing except perhaps act as a
>>> very good insulator, which is one of the two
>>> requirements for a static build up (the other being a
>>> source of charge).
>>
>>In order to prevent the coating causing static build up problems, the
>>engineers have arranged that it is not a good enough insulator to hold
>>a static charge.

> Actually these devices are indeed engineered to reduce
> static build up as much as possible, and in relative
> terms are only very slightly subject to static build up
> as compared to many other objects where that is not
> done. But by that token, a CRT screen can suffer
> millions of times more dust in a week than would be
> reasonable to have on the camera's sensor in several
> months.

> Which is to say that static build up has been reduced,
> but it is not eliminated.

> And I'll note that you've argued that that type of
> engineering is unnecessary because the CCD does not
> produce a static charge when operating... yet there it
> is, to help eliminate the effects you say shouldn't be
> there.

You haven't been following the argument. My claim was that contrary to
your claim the operating voltages of digital camera sensors are not
enough to cause dust attracting electrostatic charges. But that's not
the only way a surface can acquire a static charge, as you yourself
point out later in this post. Hence the need for static discharge
measures, even though the operating voltages won't cause electrostatic
dust attraction problems.

>>>>As far as I know
>>>>the camera sensor is protected by a glass screen, and that is what
>>>>gets dirty and needs to be cleaned. I can't see why an optical glass
>>>>screen should suffer any more from static problems than do your camera
>>>>lenses.
>>
>>> The camera lenses don't have a source of charge, other
>>> than interaction with dry air. And indeed, that is
>>> certainly enough to cause them to attract dust if the
>>> air is dry.
>>
>>That's not how it works -- the dust that glass attracts in dry air is
>>charged dust. The charge (to begin with) is on the dust, not the
>>glass. Unless you deliberately charge the glass by rubbing it with an
>>appropriate cloth, and it happens not to be semi-conductive (which
>>modern optical coated lenses often are on purpose) Which doesn't
>>happen on the digital sensor.

> If you pass dry air (with or without dust in it) over a
> glass surface (a high quality insulator) the glass
> surface will in fact become charged.

The verb "pass" is very important there, because of the mechanical
work involved, as is the amount of resultant charge.

> And it will in
> fact then collect dust if it exists, which will be
> attracted by, and adhere to it because of, the static
> charge.

The numbers matter. While what you say is theoretically true, you need
a certain dryness of air and strength of "passing" in order to
generate enough charge to attract dust through air. I think you'd find
it rather difficult to subject your camera to such conditions

>>>>What is more, I note that some DSLR makers use various sensor
>>>>vibration cleaning methods which they claim help to keep their sensors
>>>>dust free. These would not operate in the presence of electrical
>>>>static attraction.
>>
>>> That would be correct. The sensor is not energized when
>>> the cleaning mechanism of operating.
>>
>>Energising the sensor does not involve voltages high enough to attract
>>dust.

> Wrong. *Any* amount of static charge will attract dust.

Yes, theoretically in a gravity free vacuum. Not through our everyday
air. Not only are distances involved, which though small are very
important, but at the size of a dust particle the hurly burly of
molecular thermal motion and collision is involved.

> Any any amount of voltage can be used to generate a
> static charge, plus as noted above, an external source
> is not even necessary (though it will greatly increase the
> static charge that can be generated).

I think our terminology may be too loo