Where is the dust

[norn iron]

Have a look at image 37 and you should see what looks like dust in the sky area, then look at image 38 which was taken immediatly after No 37 and the spots have dissapeared.
This is happening with quite a few shots but the spots are not in the same place which would happen if the dust was on the sensor.
Is it possible that the marks are on the compact flash card ? ( I just recently purchased the 8GB card from My Memory)

I have tried using the Dust Delete Data with Canon DPP but that doesn't work as the Dust Delete Data is blanked out which means that there is no dust to Delete

I am using a Canon 40D with a Canon 24-105 IS Lens.

http://dpnow.com/galleries//data//564/thumbs/37_1_of_1_.jpg (http://dpnow.com/galleries//showphoto.php?photo=12043)http://dpnow.com/galleries//data//564/thumbs/38_1_of_1_.jpg (http://dpnow.com/galleries//showphoto.php?photo=12044)

[coupekid]

Have a look at image 37 and you should see what looks like dust in the sky area, then look at image 38 which was taken immediatly after No 37 and the spots have dissapeared.
This is happening with quite a few shots but the spots are not in the same place which would happen if the dust was on the sensor.
Is it possible that the marks are on the compact flash card ? ( I just recently purchased the 8GB card from My Memory)

I have tried using the Dust Delete Data with Canon DPP but that doesn't work as the Dust Delete Data is blanked out which means that there is no dust to Delete

I am using a Canon 40D with a Canon 24-105 IS Lens.


My immediate question I asked myself was why on earth shoot at f18? that will accentuate anything you have on the sensor!

I can only guess that the camera was switched off after the first one, as the 40D has an in-built cleaning system, I believe it vibrates, so it may have just moved the specs also?

[Pol]

I'm inclined to agree with Ben's analysis of what's probably happened here.

I don't use Canon but I have a Pentax K10D and I've occasionally had something similar happen - though usually only maybe a couple of fairly large spots when I've had to change a lens outside (never a good idea if it can be avoided). The inbuilt sensor cleaner sorted mine easily with just a couple of runs.

I must say my K10D has never shown anything like the number of spots you have on that first picture! I think I might be tempted to give the chamber a blast with a hurricane blower if my K10D ever produced that degree of spotting.

Pol

[jojo]

They sure do look like common a garden dust bunnies. If you think it has something to do with the CF card have you tried re-formatting it?

jo

[devilgas]

highly unlikely that the CF is to blame as that would be corrupting the files and therefore not manifesting itself as dust spots.
have to say, never seen anything as bad as that one image! little short of doing a wet clean yourself, try switching the camera on and off a few times with the lens removed and the hole pointing to the deck. hopefully the crap that gets dislodged during the sensor clean will drop straight out.
do you get similar results with other glass? also, i'm assuming that the glass itself is clean on both the innermost and outermost elements?

[devilgas]

My immediate question I asked myself was why on earth shoot at f18? that will accentuate anything you have on the sensor!


you sure about that ben? it'd certainly help to better define crud on the lens (even then it still wouldn't be in focus due to DoF and focal length limitations) but the sensor shouldn't be affected by the F stop. either there's dust there blocking light getting to the photosites or there isn't.
when testing for dust on my cams, i'll shoot without a lens on the body so that the ONLY thing that can possibly be dirty is the sensor, as ultimately, that's what you're looking for - obscured photosites.

[Stephen]

I wonder if this is pollen from the oilseed rape flowers. switching the camera off then on may have dislodged most of it as has been suggested, but there is still some on the second shot. I'd be inclined to use Pols method to help things along too.

[norn iron]

My immediate question I asked myself was why on earth shoot at f18? that will accentuate anything you have on the sensor!

I can only guess that the camera was switched off after the first one, as the 40D has an in-built cleaning system, I believe it vibrates, so it may have just moved the specs also?

No the camera wsn't switched off between shots

[norn iron]

I wonder if this is pollen from the oilseed rape flowers. switching the camera off then on may have dislodged most of it as has been suggested, but there is still some on the second shot. I'd be inclined to use Pols method to help things along too.

How would pollen get on the sensor with the lens attached to the camera, I didn't change lenses

[coupekid]

you sure about that ben? it'd certainly help to better define crud on the lens (even then it still wouldn't be in focus due to DoF and focal length limitations) but the sensor shouldn't be affected by the F stop. either there's dust there blocking light getting to the photosites or there isn't.
when testing for dust on my cams, i'll shoot without a lens on the body so that the ONLY thing that can possibly be dirty is the sensor, as ultimately, that's what you're looking for - obscured photosites.

try it for yourself, and youll see ;)

[devilgas]

try it for yourself, and youll see ;)

me sensors are clean, but simple physics tells me that aperture should have no effect on improving definition of dust on the sensor. the sensor doesn't care whether the image that hits it is in focus or not or whether the image has shed loads of depth of field. either the photosite has light hitting it or it doesn't, hence why i do the dust test with no lens attached.

having typed that lot, guess i'm gonna have to check it out when i get home :eek:

[Pol]

How would pollen get on the sensor with the lens attached to the camera, I didn't change lenses

I can't give you a definite answer and Ian's the person with all the technical knowledge about various cameras and their sensor cleaning systems .. but here's what I think anyway.

My k10D has a sensor cleaning system and that shakes the dust off the sensor (or low pass filter in front of the sensor). The dust falls onto specially coated areas somewhere in the chamber iirc. However - that dust is still inside the chamber so there's always the possibility it'll end up on the sensor again - requiring another run of the cleaning system.

Therefore an occasional cleaning blast with the hurricane blower is a good idea imho.

As for how it gets into the chamber - it can float in there at any time there's no lens attached. It could also get in from the rear of the lens or maybe it was there when you first bought the camera. Not all of them come with sparkling clean sensors.

I still think it's sensor spots your getting rather than anything else. Hopefully Ian might look in too as he'd be able to go into the more technical aspects of how inbuilt sensor cleaning works and what extras you can do to help keep the sensor clear.

Pol

[Patrick]

you sure about that ben? it'd certainly help to better define crud on the lens (even then it still wouldn't be in focus due to DoF and focal length limitations) but the sensor shouldn't be affected by the F stop. either there's dust there blocking light getting to the photosites or there isn't.
when testing for dust on my cams, i'll shoot without a lens on the body so that the ONLY thing that can possibly be dirty is the sensor, as ultimately, that's what you're looking for - obscured photosites.

Ben is correct increasing DOF will accentuate any dust on the sensor, test it for yourself, photo a plain surface wide open then again at f22.
I first became aware of a dust problems photographing flowers on a white ground with a macro lens stopped down to f22 and more.

Patrick

[Patrick]

Ben is correct increasing DOF will accentuate any dust on the sensor, test it for yourself, photo a plain surface wide open then again at f22.
I first became aware of a dust problems photographing flowers on a white ground with a macro lens stopped down to f22 and more.

Patrick

Consulted my trusty Encyclopaedia of Photography.
As photographers we are concerned with Depth of Field, the higher the number the greater the DOF becomes, Fine.
The f stop also effects Depth of Focus which should not be confused with Depth of Field. The two things are related but not the same thing.

Depth of Focus is to do with how the light hits the Sensor/Film known as the cone of rays, where as the photographer stops down the cone of rays is narrowed, this is what I think shows the dust in sharper relief.
Therefore testing for dust with no lens will show little, the light is too defuse to have any meaning. Dust will only be shown clearly with a lens, and be shown more strongly as the lens is stopped down. I don't actually think the lens has to be focused, just stopped down. I shall test that out for myself.

Patrick

[norn iron]

Thanks all for your help,
what is confusing me is that I have taken a lot of shots of the same scene and some show no dust while others show a lot, all with the camera set at f18 or f22. I even went out this morning to the same place and took a lot more shots with the same results.

I think I will have a go at cleaning the sensor so now I am asking what products you would recommend ?

Thanks,
Ken

[devilgas]

Thanks all for your help,

I think I will have a go at cleaning the sensor so now I am asking what products you would recommend ?

Thanks,
Ken

i use pecpads, eclipse solution and a cut down rubber spatula. honest.
never had any issues when doing this and leaves the 'sensor' squeaky clean afterwards.

[coupekid]

me sensors are clean, but simple physics tells me that aperture should have no effect on improving definition of dust on the sensor. the sensor doesn't care whether the image that hits it is in focus or not or whether the image has shed loads of depth of field. either the photosite has light hitting it or it doesn't, hence why i do the dust test with no lens attached.

having typed that lot, guess i'm gonna have to check it out when i get home :eek:

Yeah, I would check it out before applying simple physics to the equation..........then you can let us know your findings ;)

[devilgas]

Yeah, I would check it out before applying simple physics to the equation..........then you can let us know your findings ;)

i stand corrected. simple physics divvna work here.

that'll be me with the dunces hat stood in't corner then *party

could only get marks to show up at F22 - F32. anything less than that and they got blurred nicely to the point where they're not visible (even at F18)....which is probs why i thought my sensor was clean - rarely shoot about F8, and usually it's 2.8 or 4 *LOL