Mystery question

[PacAce]

Here's a question. How does the dust get to the sensor when the focal plane shutter is closed most of the time and only opens when you take a shot and only for a split second in most cases? ???

Do the Canon engineers need to learn about fluid dynamics to see how a moving shutter can create a vortex that can suck up dust in the light box and shoot them towards the sensor in order to be able to device a way to prevent this from happening?

Or is there so much static charge on the sensor that the dust particles can't help but be attracted to them every time the shutter opens?

:mrgreen:

[defordphoto]

Anytime you change a lens the camera is subject to infiltration. From there it's just a matter of time before a chunk makes its way to the sensor. It's probably a good idea for us camera owners to be proactive and blow out the cavity from time to time to reduce to the chance of dust infiltration. However, it will always be a problem. All that can be done is to reduce the chance of infiltration. It can never be completely removed.

[Cadwell]

Or is there so much static charge on the sensor that the dust particles can't help but be attracted to them every time the shutter opens?

:mrgreen:

I've heard the static blamed elsewhere....

[Jim_T]

Here's a question. How does the dust get to the sensor when the focal plane shutter is closed most of the time and only opens when you take a shot and only for a split second in most cases? ???

?? The focal plane shutter is OPEN most of the time.. (Take your lens off and check ) :) The curtains are activated in sync with the mirror flipping up.

Do the Canon engineers need to learn about fluid dynamics to see how a moving shutter can create a vortex that can suck up dust in the light box and shoot them towards the sensor in order to be able to device a way to prevent this from happening?

Actually, I'd suspect the mirror movement causes much more air movment than the shutter. Perhaps that's what you are referring to ? If so.. Without abandoning the SLR system, not much can be done. The mirror is an integral part.

Or is there so much static charge on the sensor that the dust particles can't help but be attracted to them every time the shutter opens?

I've heard that dust is attracted by a static charge.. But I've seen no solid proof to substantiate this..

I've had my 10D for close to a year.. I have had dust on the sensor, but it's never been a real problem..

[PacAce]

Here's a question. How does the dust get to the sensor when the focal plane shutter is closed most of the time and only opens when you take a shot and only for a split second in most cases? ???

?? The focal plane shutter is OPEN most of the time.. (Take your lens off and check ) :) The curtains are activated in sync with the mirror flipping up.


Does that mean the mirror is up all the time, too? ??? :lol:
The focal plane shutter is just another fancy word for the curtain. :D


Do the Canon engineers need to learn about fluid dynamics to see how a moving shutter can create a vortex that can suck up dust in the light box and shoot them towards the sensor in order to be able to device a way to prevent this from happening?

Actually, I'd suspect the mirror movement causes much more air movment than the shutter. Perhaps that's what you are referring to ? If so.. Without abandoning the SLR system, not much can be done. The mirror is an integral part.


Hmm, you might have a point there. Never gave the mirror much thought as the likely culprit that's agitating the dusts in the light box.


Or is there so much static charge on the sensor that the dust particles can't help but be attracted to them every time the shutter opens?

I've heard that dust is attracted by a static charge.. But I've seen no solid proof to substantiate this..

I've had my 10D for close to a year.. I have had dust on the sensor, but it's never been a real problem..

To be honest with you, dust has never been a problem on my sensor, too, although I know I've had a couple on the sensor since half a year ago. I did notice that they tend to migrate around a lot but it didn't bother me any.

I did take my 10D in to the NJ service center two days ago to have them calibrate my lenses and the camera and also clean my sensor while they have the camera. I wanted to get all these things done because the warranty expires the middle of next month.

[Jim_T]

Sigh.. I just peeked under the mirror on my 10D.. You are right.. The shutter is closed when not taking pictures.. It's moved when you go into cleaning mode so the mirror pops up and there's the sensor.

I know the shutters are closed in film cameras, but somehow assumed it was open in digicams, since unwanted light falling on an idle sensor won't ruin things the same way light falling on film will.

Actuallly, the shutter should protect the sensor from dust... anything falling on the curtain can't land on the sensor..

Of course movement of the sensor and mirror will still stir up dust.. Not much can be done about that :)

[EXA1a]

Summary:
Changing lenses and using certain push-pull lenses brings dust into the mirror case.
The shutter curtain is normally closed and only opens for exposure.
The shutter curtain moves virtually no air because its blades are moving vertivally.
The mirror causes some turbulences within the mirror case that could "blow" dusty air into the sensor room during exposure.
Even without turbulences the static sensor/sensor filter could attract dust floating in the mirror case while shutter is open, especially during long exposures.

How can you (theoretically) avoid/reduce sensor dust?
Don't change lenses too often
Don't change lenses in places where air is dusty
Hold camera face down when changing lenses
Don't do long exposures
Blow dust out of the mirror case frequently
Don't use push-pull zooms
Use sealed lenses
Keep camera in a clean bag when not in use
Use mirror lock-up

For the camera makers:
How to avoid sensor dust technically? Here's what I came up with:

Camera makers could avoid sensor dust problems by sealing the sensor room with a glass plate in front of (or right behind) the shutter. A piece of glass would probably not attract that much dust and could easier be cleaned or exchanged. Disadvantage: you add another glass which could cause optical disturbances.

Let's see what they do about this nasty little problem...

--Jens--

[robertwgross]

You aren't cleaning the sensor surface when you clean the sensor.

The actual sensor (a chip) has a clear anti-aliasing filter over the actual surface. So, when you say you are cleaning the sensor, you are actually cleaning the filter. I don't think another piece of glass in there is going to make it better or worse.

---Bob Gross---

[perfectpixel]

Do the Canon engineers need to learn about fluid dynamics to see how a moving shutter can create a vortex that can suck up dust in the light box and shoot them towards the sensor in order to be able to device a way to prevent this from happening?
:mrgreen:

I believe the new Pentax (is it Olympus?) dSLR has a "ultrasonic" (or something like that) sensor cleaning gizmo onboard. Sounds like a great idea!


Or is there so much static charge on the sensor that the dust particles can't help but be attracted to them every time the shutter opens?
:mrgreen:
Well, unlike some, I didn't peek under my 10D mirror, but I dd notice how much dust there is on my TV screen :wink: same physics at work there :D

[pradeep1]

Did you guys hear about that new camera from Olympus or maybe Minolta that has an ultrasonic vibration mode for the sensor to knock off dust and all. Canon needs that for their dSLRs.

[CyberDyneSystems]

Olympus has the ultrasonic dust vibrator... :shock:

You know that rat bastard company Sigma had an innovative Idea.... :roll:

They sealed the opening with a replaceable peice of optical glass (being an optics company they could do that.. to bad Canon doesn't make optics too .. :wink: wait a MINUTE!!!!!!!

http://www.dpreview.com/reviews/SigmaSD9/Images/dustprotector-001.jpg

The glass is easy to clean,. (as it is not recessed as far as the CCD) and if you scratch it,. it can be replaced. (By Sigma)
And,. as seen in the image above,. it is rectangular.. further serving as a hood to stop funky extra light from gaining acces to the inside of the camera.. (of course most lenses do this too)

And Considering that the images from the SD9/10 are said to be the sharpest most color vibrant images from ANY 3 MP camera made,. I would have to deduce that the the glass does not detract from the image quality too much.

By installing the protective glass, no dust can enter the camera ,.. Of course Sigma has thought of everything here,.. and to keep us from getting to disapointed by a lack of dust on our sensors,. Sigma has seen fit to "factory install" a modest amount of dust in most SD9's sealed in semipermanantly BEHIND the protective glass! Thanks Sigma! :mrgreen:

I wish Canon would at least give us the option.. like a screw in filter. I bet the photographers in Iraq would have "opted" to risk some image degradation and kept those peices of glass in. Imagine being able to seal the front of your camera from invasive dust and moisure.. what an idea!

We have the option to screw a piece of $54.00 glass in front of our $1,800.00 L lenses... and most of us "opt" to do so,.. I bet a lot of us would do the same if the glass was at the other end :-)

I know I would.