Sensor dust Nikon D80

On Jan 13, 6:44 pm, Cyberiade.it Anonymous Remailer
<anonym....DeleteThis@remailer.cyberiade.it> wrote:
> Chris Malcolm wrote:
> > Floyd L. Davidson <fl....DeleteThis@apaflo.com> wrote:
> > > Jim Townsend <n....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.
>
> ROTFL!
>
> 1. Static charge is measured in Jules, not volts.
>
> 2. Attracting dust through air only requires static charges in the
> millionth of a Jule range.

Ñå, ôá èåëåéò êáé ôá ëåò, ç óïõ îåöåõãïõí?!

>
> 3. You, are an idiot.
>
>

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

Who said it did?

> 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.

Exactly.

> 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.

Of course not. All that matters is the voltage, not where it comes
from.

> 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???

No, because charges of that voltage migrate to surfaces and
concentrate on convexities, so being generated locally in the hair
that's where the thousands of volts stay. But as Tesla's hair-raising
experiments demostrated, you can if you like -- in appropriate
conditions -- quite safely raise your entire body to tens of thousands
of volts above ground potential.

>>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!

Of course not. I can't imagine who you're arguing with here. It
doesn't seem to be anything I've said.

>>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.

I was responding to a remark of yours which seemed to imply that the
low voltages of camera sensor operation were enough to *attract*
dust. *Attracting* dust through air requires at least some hundreds of
volts, and it doesn't matter how they're produced. Stroking a cat (or
your camera) is just as good a way as connecting up to a high voltage
power supply such as you can find in a CRT based monitor or TV.

You're now talking not about dust *attraction* but dust
*adhesion*. There is a huge difference between those two. If the very
trivial dust adhesion forces (easily broken by a puff of air) is all
you ever meant to be talking about then forget my argument.
Considerable care is taken in the engineering of digital cameras and
their sensors to prevent the problems of electrostatic dust
*attaction* which do involve hundreds of volts, but if you only meant
to refer to normal contact adhesion potentials then that's all
irrelevant.

Note however that that kind of *adhesion* potential difference between
dust and the sensor protection surface is low and local enough that it
has no connection with the electricity involved in sensor operation.

--
Chris Malcolm cam RemoveThis @infirmatics.ed.ac.uk DoD #205
IPAB, Informatics, JCMB, King's Buildings, Edinburgh, EH9 3JZ, UK
[http://www.dai.ed.ac.uk/homes/cam/]