Sensor Dust - slaying the myths

[huyzer]

Hi claypaws,

How about this? I remember a suggestion similar to this when I was at school in the darkroom. They say to run the shower if you want a less dusty environment to hang the film. Maybe they meant a hot shower where steam forms so as to drag all the dust down with it. Then wait for a while (or maybe run the cold shower if impatient?), then hang your film to dry (or change lens, or clean sensor). Of course I don't suggest going in when the air is still moist.

Take care,
Huy

This is based on the fact that water cleans dust out of the air. Yes
it does but it takes a very long time and only removes dust from air
that streams towards the shower. If you are going to run the shower
for many hours and constantly fan the air towards the shower, it will
clean the air. Otherwise it will have very little benefit. If you run
the shower continuously for days, then gradually the dust will
disperse towards the shower and be gradually removed. This may have a
noticeable effect after a week or so of continuous running of the
shower!
--
******************************************************
I have a home on pbase
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If you have the time to look
******************************************************

 

[Walter S Matthews]

I don't know!!!
I know they use clean rooms but that's all I know about them.
Sorry....

 

[claypaws]

Hi claypaws,

How about this? I remember a suggestion similar to this when I was
at school in the darkroom. They say to run the shower if you want a
less dusty environment to hang the film. Maybe they meant a hot
shower where steam forms so as to drag all the dust down with it.
Then wait for a while (or maybe run the cold shower if impatient?),
then hang your film to dry (or change lens, or clean sensor). Of
course I don't suggest going in when the air is still moist.

That is funny, Huy! Maybe immersing the camera under the shower would help to wash the dust off it ;-)

More seriously the hot shower to clean the air would be a bad idea for sensors as the droplets of water would quite likely deposit their dust load very nicely onto the sensor. Ouch!!

On your hard drive question (to which I do not know the answer), I remember when we used to run mainframe computer rooms with elaborate air filtering systems and double-door entry to protect the massive and expensive hard disks from crashing due to dust. Those "massive" disks held 200MB each and cost about £10k each. Now you can buy 1TB for £100.
--
******************************************************
I have a home on pbase
http://www.pbase.com/claypaws/
If you have the time to look
******************************************************

 

[Thom Hogan]

This myth is usually taken for granted as self-evident truth.

And I find your arguments on this to be simplistic.

Let's go to the lab. The air in which you're operating either has some level of dust in it. In dry climates that can actually be quite high, in wet climates, it can be quite low. But let's assume two cases for a moment: (1) High dust content in air; and (2) Little or no dust content in air.

1. 2 is easy to deal with: in neither case, changing lenses or pumping zooms, is it likely that any significant level of dust is transported from the general air around you into the mirror box. It would take a great deal of zooming or lens changing to change the mirror box environment (and that assumes that the low dust air IN the mirror box is going somewhere).

1. 1 is more interesting. Your argument boils down to air currents. You argue that zooming is more problematic than changing lenses. But your argument is completely anecdotal. You haven't actually measured how much displacement there is in each case. Moreover, you haven't taken into account the outward effect of half of that zooming. Sorry, but after more than a decade of using these products, I don't see evidence that one or the other is worse. You'll have be a lot more specific and provide some real numbers to convince me otherwise.

--
Thom Hogan
author, Complete Guides to Nikon bodies (19 and counting)
http://www.bythom.com

 

[Thom Hogan]

Because dust moves with the air stream, it is little affected by
gravity over the short term.

While true, this ignores a basic fact: some of the things in the air are heavy enough that this isn't true for them. One of the reasons why I first wrote many years ago that you should use a downward mount if possible and continue to repeat it today has to do with pollens. They are heavy enough to settle into the mirror box when it is exposed. And they are amongst the worst offenders when it comes to sensor cleaning: they're very hard to remove.

--
Thom Hogan
author, Complete Guides to Nikon bodies (19 and counting)
http://www.bythom.com

 

[Thom Hogan]

This is an attractive myth but it is wrong.

Dust clinging to the filter is due to two things: static charge and surface tension. To break those bonds you need a force. An airstream can be enough force to do so. And I've got plenty of lab results to prove this one.

Also, let's be very careful with language. "remove...from the sensor." No, what we're doing here is dislodging the dust from its position on the filter. The dust isn't actually removed. Indeed, there's a strong likelihood that it will get back on that filter (just store the camera on its back and see what happens ; ).

--
Thom Hogan
author, Complete Guides to Nikon bodies (19 and counting)
http://www.bythom.com

 

[huyzer]

Hi claypaws,

More seriously the hot shower to clean the air would be a bad idea
for sensors as the droplets of water would quite likely deposit their
dust load very nicely onto the sensor. Ouch!!

Well, of course I don't mean to walk right in afterwards, or even 15-20 minutes afterwards; whatever seems correct/use your own discretion. The intent would be to have that room nice and closed, with no disturbance, to keep it clean. After all that moisture has dissipated, then you have a dust-free room for cleaning, or hanging your film to dry.

On your hard drive question (to which I do not know the answer), I
remember when we used to run mainframe computer rooms with elaborate
air filtering systems and double-door entry to protect the massive
and expensive hard disks from crashing due to dust. Those "massive"
disks held 200MB each and cost about £10k each. Now you can buy 1TB
for £100.

Hmm, puts things in perspective.

Welps, take care,
Huy

 

[claypaws]

This is an attractive myth but it is wrong.

Dust clinging to the filter is due to two things: static charge and
surface tension. To break those bonds you need a force. An airstream
can be enough force to do so. And I've got plenty of lab results to
prove this one.

I did not say it could not be dislodged with blower. I agree entirely that an airstream can break the bonds.

Also, let's be very careful with language. "remove...from the
sensor." No, what we're doing here is dislodging the dust from its
position on the filter. The dust isn't actually removed. Indeed,
there's a strong likelihood that it will get back on that filter
(just store the camera on its back and see what happens ; ).

If you read what I said, I think you will find that it is almost exactly what you say above.

I said:

Once the stream hits the sensor or other parts of the chamber, it
becomes a turbulent stream going in random directions. If the blower
dislodges any dust from the sensor as well as adding some to it, the
dislodged dust will go in random directions. The sensor chamber is a
box with six sides of which one is open. There is roughly a 1 in 6
probability that the randomly directed dust will therefore exit the
chamber. There is a 5 in 6 probability that it will hit one of the
other 5 surfaces. There is a 4 in 6 probability that it will hit a
surface that is not the sensor. So the most likely outcome is that
the dislodged dust will hit the shutter curtain or the velvety
coating of the sensor chamber, where it will become lodged. There is
no physics that justifies the misconception that the dust is simply
going to neatly turn around and go straight out of the open face of
the sensor chamber without colliding with anything. Superficially,
the sensor appears to be cleaner. The relief is temporary. That dust,
now lodged in the shutter curtain or chamber, will break free during
camera operation and take up a new position on the electrostatically
charged sensor.

I did not actually mention the fact that it is the filter that we are cleaning. I think the use of the word "sensor" in this context was merely common usage, as in "methods of cleaning the sensor", or Photosolutions' "Sensor Swabs". I have never seen any product called "Sensor AA filter cleaning solution".
--
******************************************************
I have a home on pbase
http://www.pbase.com/claypaws/
If you have the time to look
******************************************************

 

[claypaws]

Because dust moves with the air stream, it is little affected by
gravity over the short term.

While true, this ignores a basic fact: some of the things in the air
are heavy enough that this isn't true for them.

I think I have now been persuaded on this one! There does seem to be justification for keeping the camera pointing down, or at least not up, to avoid those things that do move under gravity.

why I first wrote many years ago that you should use a downward mount
if possible and continue to repeat it today has to do with pollens.
They are heavy enough to settle into the mirror box when it is
exposed. And they are amongst the worst offenders when it comes to
sensor cleaning: they're very hard to remove.

Whilst I accept the argument about things that are heavier than air, I am not sure how many pollens are in that category. I can believe that there are some that are. But surely a lot are not. Hay fever sufferers are affected by breathing in pollen. I assume they do not get the pollen by walking around with thier heads pointing upwards. Do they not breathe in the airborne stuff? It cannot be avoided by a change of head position and I do not see why a camera position would avoid it either.

However, if any pollens are heavy enough to descend under gravity in the time it takes to change a lens, I agree it is a good idea to position the camera to reduce the chance. Hence I am persuaded.

It is interesting that you point out how difficult pollen is to remove. I wonder if that has to do with its complex surface geometry which is, after all, "designed" in nature to stick to insects for transfer.

--
******************************************************
I have a home on pbase
http://www.pbase.com/claypaws/
If you have the time to look
******************************************************

 

[claypaws]

This myth is usually taken for granted as self-evident truth.

And I find your arguments on this to be simplistic.

I did not claim to offer the results of a statistical analysis. But the status of lens changing as the main source of dust is never presented in anything other than a simplistic way either. It is usually just assumed. At least Photosolutions Inc. do consider the effect of zooming to be important. They print it on the box. And they do not mention lens changing.

Let's go to the lab. The air in which you're operating either has
some level of dust in it. In dry climates that can actually be quite
high, in wet climates, it can be quite low. But let's assume two
cases for a moment: (1) High dust content in air; and (2) Little or
no dust content in air.

1. 2 is easy to deal with: in neither case, changing lenses or pumping

zooms, is it likely that any significant level of dust is transported
from the general air around you into the mirror box. It would take a
great deal of zooming or lens changing to change the mirror box
environment (and that assumes that the low dust air IN the mirror box
is going somewhere).

I agree. I do not think clean environments are much of a hazard for zooming or lens changing.

1. 1 is more interesting. Your argument boils down to air currents. You

argue that zooming is more problematic than changing lenses. But your
argument is completely anecdotal. You haven't actually measured how
much displacement there is in each case. Moreover, you haven't taken
into account the outward effect of half of that zooming.

What I have tried to argue is indeed based on air currents.

I do not think that the air displacement volume is the item of importance. I am not sure what you mean by air displacement "there is in each case". Air displacement during lens changing? Surely the lens changing argument is that of "exposing" the sensor (or filter, if you prefer the term) and considering it as "protected" when any lens is in place. But maybe you mean the air displacement due to wind gusts etc while the lens is off the camera.

It is true that I did not address the outward flow of air through the zoom lens. Perhaps it might have a "vacuum-cleaning" effect. Or perhaps, rather like the blower brush, it might simply dislodge particles and then allow them to hit the chamber walls. It is an interesting point though.

Sorry, but
after more than a decade of using these products, I don't see
evidence that one or the other is worse.

And that is a decade of anecdotal evidence. I do not deny, however, that I did not offer any evidence at all. So your anecdotal comment is interesting. It does at least not come down in favour of lens changing as the predominant source of contamination. Photosolutions do choose only to mention zooming and not lens changing on the Sensor Swabs box. I do not know if their comment is evidence-based. Sometimes, anecdotal evidence is all we have.

You'll have be a lot more
specific and provide some real numbers to convince me otherwise.

I agree that more than that is needed to convince a sceptic and that scepticism is a virtue.

I wish I could be more specific. Presumably, the "numbers" that would support, or contradict, what I suggested would be some kind of statistical experiment.

We would need to operate models of the same camera alongside each other in the same environment. Both cameras would be throroughly cleaned first, cleaning the sensor chamber and the sensor (filter!). One camera would have a permanently mounted variable-volume zoom lens and the other camera would use only internal focus primes and these primes would be changed as normal. Then over a period of time, test photos would be taken to compare the dust accumulations on the two cameras.

For statistical significance, the experiment would be conducted on a large number of pairs of cameras and a paired statistical test would be applied to test, or reject, the hypothesis that 'there is no difference in contamination levels between a "zoomed" camera and a "prime" camera'.

Alas, I have no resources to commission such an experiment.

I do not think you were wanting figures on the effect of air streams on particles of various masses and surface areas.

Thank you for arguing though. It is important to challenge ideas and I appreciate your taking time to do so.

--
******************************************************
I have a home on pbase
http://www.pbase.com/claypaws/
If you have the time to look
******************************************************

 

[FlossTycoon]

I have taken a look at those lenses I have which are not internal zoom and focus. Darned if I can find any opening on the rear which is open to the sensor area of the camera. For the most part there is a rear element which is solidly mounted to a metal plate for the full circumference of the element. This metal plate is either part of the lens mount or again secured the full circumference of the plate to the lens mount. If there is air sucked in or pushed out it seems to be on the outside of the lens barrel at the focus or zoom ring. Even the teles with a recessed rear element do not seem to move air at the rear element.

Am I missing something here?

In the early days the most common dust bunnies in the S3 seemed to be left over cuttings from the thread cutting operations for all of the internal screws in the body. Those seem to be mostly gone now.
--
Alan, in Montana
Photos are cached here,

http://radphotos.net/index.php?option=com_copperminevis&Itemid=33&place=gallery&cat=10069

 

[claypaws]

There is no obviously visible exit for the air, I agree. The best way to show it is to feel it. Hold the lens up in front of your face with the rear end near your lips. Then zoom the lens. You will feel the air blowing on your lips.

Interesting about the thread-cutting crud in the S3. That might explain why my S3 was plagued by bunnies for its first 3 months. And why they were so impossible to remove that Fuji replaced my sensor.

--
******************************************************
I have a home on pbase
http://www.pbase.com/claypaws/
If you have the time to look
******************************************************

 

[Thom Hogan]

I did not claim to offer the results of a statistical analysis. But
the status of lens changing as the main source of dust is never
presented in anything other than a simplistic way either.

Anyone who knows me knows that I'm an analytical guy. And I'm not a zoomer. So when I when I started seeing dust buildups way back in the olden days of digital I did some quick experiments. I carried two identical cameras with me into various environments. On one, I changed lenses, on the other I didn't. Do you care to guess which one had more dust? ; )

--
Thom Hogan
author, Complete Guides to Nikon bodies (19 and counting)
http://www.bythom.com

 

[Walter S Matthews]

Before you tell us the answer let me put out some more data.

In my former life where i had access to the worlds newest and most expensive clean room we performed a series of experiments. The experiments led to us covering everyone who entered the clean room with a covering that completely encases each person and all air that each person exhales is passed through a hepa filter before it is allowed to return to the air in the room.

We set up a particle counter and tested several things.

First is skin.

Skin holds a large amoung of particles that are moved around and moved about even when you simply move your arm from location to location without shaking your wrist or elbow. If the skin has been freshly washed it ends up just as particle laden as unwashed skin but the particles take longer to settle (skin flakes are very light and normal dust in the air is considerable heavier). If you put an oily residue, (baby oil) on the skin you can eliminate the particle generation that your arm generates. It takes about 2 to 3 hours for skin that has been treated with baby oil to start generating particles again when that aim is moved. Make up is a major source of particle contamination and you would be amazed at how much makup falls off a face in the course of a days work.

Clothing has a large number of particles and particles from clothes take a lot longer to settle than particles from the skin. When you, move your arm with a white dress shirt with the button buttoned in a particle detection beam, thousands of particles are thrown out and those particles settle down to hundreds within seconds and to under 10 within a minute. In other words those particles are not suspended by brownian movement and they are settling under the force of gravity. If you rub the skin on your arm in the particle beam area you generate hundreds of thousands of particles and they take a lot longer to settle. However, they do settle within a minute. Particles of skin are a major source of contamination in semiconductor processing because 1. They end up having a coating of oil that makes them stick to where ever they land and they contain sodium that is a bad actor in the devices.

OK, so you change a lens. When you change that lens you are throwing particles into the air around the lens opening from your hands and just from moving the lens in its mount. When you remove the lens you have moved metal or plastic against metal or plastic and that action is generating large particles that are affected by gravity.

The worst kind of particle is one that has a residual charge on it. It will be attracted to a neurtal surface and it will attract other particles with opposite charge until that charrge has been neutralized. While the initial charged particle can be very small it can grow to a considerable size depending on the electrical environment of the area and the kind of equipment that is being used in the area. We ended up installing ionization points at 2 foot intervals in the non hepa scrubbed change room areas because the ionized air imparted a residual charge to all particles and those particles then tended to stick to the walls and they stayed out of the clean room.

A drop of oil or grease or for that matter saliva, are all bad actors because they can serve as loci for more particles to accumulate.

Early morning outdoor moist air is generally a lot cleaner than indoor air and a lot ceaner than air from the same place in the afternoon.

 

[huyzer]

Hi Mr. Matthews,

No problem.

Take care,
Huy

I don't know!!!
I know they use clean rooms but that's all I know about them.
Sorry....

 

[FlossTycoon]

I think I am fortunate to live out west where the humidity is generally low. So far everything had bLown off the sensor when I have had to clean it. I have yet to find the need to use any sort of liquid and I hope to keep it that way. I may purchase one of those brushes if something gets stuck but I wonder if the liquid cleaners can sometimes just glue things to the sensor at times. I am sure the folks in the high humidity coastal areas have more trouble with bunnies sticking than us westerners.

I will go now and try the zooming across the lips test to see if my Tamron 200mm-400mm zoom passes gas in my face.

--
Alan, in Montana
Photos are cached here,

http://radphotos.net/index.php?option=com_copperminevis&Itemid=33&place=gallery&cat=10069

 

[BobsYourUncle]

Be sure to have the video camera running. I'd like to see this

Bob

I think I am fortunate to live out west where the humidity is
generally low. So far everything had bLown off the sensor when I
have had to clean it. I have yet to find the need to use any sort of
liquid and I hope to keep it that way. I may purchase one of those
brushes if something gets stuck but I wonder if the liquid cleaners
can sometimes just glue things to the sensor at times. I am sure the
folks in the high humidity coastal areas have more trouble with
bunnies sticking than us westerners.

I will go now and try the zooming across the lips test to see if my
Tamron 200mm-400mm zoom passes gas in my face.

--
Alan, in Montana
Photos are cached here,

http://radphotos.net/index.php?option=com_copperminevis&Itemid=33&place=gallery&cat=10069

 

[FlossTycoon]

I haven't made the switch to the new D90 so I have no video mode.

Most home videos just bore me. I mostly avoid any temptation to move in that direction myself. If I notice the longer lenses fluffing my hair around I will get hold of a borrowed video camera and youtube it.

--
Alan, in Montana
Photos are cached here,

http://radphotos.net/index.php?option=com_copperminevis&Itemid=33&place=gallery&cat=10069

 

[Paulo Abreu]

Hi Stephen,

Interesting thread, I might agree with you in many points and my experience with sensor cleaning is coincident with your thoughts, here mine:

As I said a couple of months ago, my S5 sensor is absolutely clean and now I change lens more than ever ... but... almost all my lenses are zooms! Well, none is push/pull design but so it isn't the Nikon 14-24 than someone referred that pushed a lot of air into the body.

My S2 used to collect a lot of "spots", not necessarly "dust". Actually, most of those spots were lubricant oil from the shutter mechanism - these were hard to clean and needed a few of wet cleaning steps to disapear.

Altought I agree it can be hard for the "heavy" dust spots to hit the sensor, I always take gravity in account when chaging lenses and IMHO it can make a difference in cleaness at least on mirror chamber ...

I would never use any kind of vacuum cleaner nearby the mirror chamber - the vortex it makes I believe is very very bad, it will acelerate those "invisible" dust particles into the speed of light and spread them everywhere ... I believe in a hand rubber blower when used very locally.

But for me this is all old news and all in respect to S2. In S5, sensor dust in a non issue - I only used a rubber blower twice to get rid of some dust visible in the in the viewfinder.

My 2 cents
Regards
--
Paulo Abreu,

'It is not worthy to make a video of your life - just keep the best moments in pictures!'

 

[BJN]

While I agree that changing lenses isn't a major concern for admitting dust to the camera, it's absolutely a contributor that you need to be mindful of. I guarantee you that if you're very casual about leaving your camera lensless while you take your time changing lenses, dust will enter the mirror chamber and that dust can eventually find itself on the sensor.

It's sensible to expedite lens changes, to watch the rear end of a lens and blow or brush off any obvious dust it picked up while off the camera, and to avoid lens changes in very dusty evironments (when practical). You don't have to be obsessive about these precautions, but a little care is prudent and may extend time between cleanings.

If you really believe your absolute statement, you'd better be prepared to cite convincing test evidence.
--
BJ Nicholls
SLC, UT