View Full Version : of digital cameras and sensor dust
Overconfidence
07-19-2008, 13:11
I have a few questions for those of you who may be more experienced in this area.
We all know that sensor dust is an issue on interchangeable-lens digital cameras. However, I think that it is even more critical on digital rangefinders.
When using an SLR, you will often shoot wide open (or nearly wide open) and autofocus on your subject. On my digital SLR, sensor dust is invisible up to about f/11, but it is noticeable at f/16 and f/22. This is no big deal for me because for the type of shooting I do, I rarely go about f/8. But when I shoot film (particularly street photography), I like to stop down to f/16 and zone focus.
I'm scared that if I were to get a digital rangefinder in the future, sensor dust would limit me and I would be forced to use larger apertures to avoid sensor dust.
In a digital camera, is the sensor actually always exposed to the mirror chamber/lens chamber/that area between the lens and the sensor? I would assume that the shutter would be covering it (except for the 1/250th or however long it takes for the shutter to travel) and that you wouldn't really get all that much dust on the sensor (I rarely see any kind of dust on my film, and obviously the shutter is covering the film).
Also, shouldn't there be a pretty easy way to avoid this dust? We already have the dust "shake-off" systems, but these are pretty inefficient. I would think that it would be easy enough to have some kind of sacrificial static or otherwise strips in the camera body that would attract dust, but I don't know the technical implications of that.
Another issue with rangefinders in particular is the angle at which the light hits the film/sensor - would it be impossible to include the basic shake-off systems or filters if you're trying to build a thin/sensitive/whatever sensor with a complicated microlens structure?
These are just my curious ramblings, please give any insight you can or explain the obvious to me. Cheers!
We already have the dust "shake-off" systems, but these are pretty inefficient.
I have had an Olympus digital SLR for almost a year without dust problems, and India is a damned dusty place. Olympus give their system the absurd name Super Sonic Wave Filter.
My M8 seems to be a dust magnet.
I noticed this when blowing out the M8 with a bulb blower: holding the camera in my left hand, with my left palm over the LCD and using my right hand to squeeze the bulb of the rocket blower to blow air up into the camera, I can feel air blowing on my left hand. It's blowing right through the camera.
I've become reluctant to even change lenses on my M8 because even with very quick changes and the camera always in a clean environment, the thing manages to attract dust.
If I only shot under f/2 I wouldn't care. But I use the M8 with flash and smaller apertures so much that dust matters.
No such dust problems with my R-D1.
I have used my M8 together with, first, my 1Ds II, and later with my new 1Ds III. To get good pictures I stop down my DSLR shots just as much as the ones I take with my M8. To my experience, the M8 is just as vulnurable to dust as 1Ds II. I only used a blower to clean the sensor. Which is only limited efficient. But I never touch the sensor with anything myself. I leave that to a local Canon serice shop here in Oslo.
The 1Ds III is a totally different animal altogether. This is the first camera I have with this sensor 'shake' system. It works wonders. Along comes also a software solution with further a possibility to eliminate spots. I have not had to use yet, which shows how effective the sensor shaker is.
One more thing; the M8 is easier to clean than the 1Ds II because it is not Full Frame.
photomoof
07-19-2008, 14:41
On my digital SLR, sensor dust is invisible up to about f/11, but it is noticeable at f/16 and f/22. This is no big deal for me because for the type of shooting I do, I rarely go about f/8. But when I shoot film (particularly street photography), I like to stop down to f/16 and zone focus.
I cannot imagine why this would be, sensor dust is on the sensor -- the f-stop should have no effect whatsoever! Dust is dust, it will show no matter what you do with the lens.
When looking for sensor dust I sometimes put a frosted glass over the camera and shoot into my light table. I can spot each and every one in a nano-second, and spot when they are gone. By doing that the dust is not upside down and reversed.
Anyway, it is sort of true that RFs like the M8 might be a little more exposed, but dirt is dirt.
I personally never change lenses on digital cameras in the field, but carry two bodies.
Overconfidence
07-19-2008, 15:07
I cannot imagine why this would be, sensor dust is on the sensor -- the f-stop should have no effect whatsoever! Dust is dust, it will show no matter what you do with the lens.
This is untrue. A wide open lens will not show dust, whereas a heavily stopped-down lens will. Something to do with diffraction and the way the light hits the sensor... the best explanation I read that made sense was that if a lens is wide open, there are many more pathes for the light to take from the aperture to the sensor (and the dust actually resides on a piece of glass covering the sensor), whereas at f/22 light can not angle behind the pieces of dust and thus they leave a clearer shadow.
I have a canon 40D which includes the ultrasonic shake-off (or whatever they call it these days) and I have several dust spots, none of which are very visible at f/11 or below. These dust spots are, admittedly, very small, and if I were to extrapolate their actual size from the size of the dust in pixels, I would imagine that even a good blowing-off wouldn't be able to get them.
Here are a couple enhanced-contrast images I just took of a plain background that illustrate this (keep in mind I've put about 15k clicks on this over about nine months and countless quick lens changes and never even attempted to manually clean):
f/11:
http://img301.imageshack.us/img301/9279/img6292vw4.jpg
f/29
http://img301.imageshack.us/img301/4609/img6291xb9.jpg
I have never seen dust in any of my pictures, except for perhaps one or two landscapes at f/16 where I tried darkening the sky in post-processing. Admittedly my viewfinder is much, much dirtier (due to dust and gunk sticking to the focusing screen), but I am actually quite careful when switching lenses... I just happen to switch them often since I use mostly primes on my SLR, and I'd imagine on an interchangeable-lens rangefinder you'd want to be able to do this.
For you M8 owners... the shutter does in fact cover the sensor when changes lenses, right? So it's only during exposure when dust can sneak onto the sensor? Or am I missing something?
photomoof
07-19-2008, 15:17
Or am I missing something?
Well for one thing you are missing the three HUGE spots on the first image (i raised the contrast to make them more visible).
And yes in some cases using lenses wide open so light bounces off the surface of the rear element, will cause the spots to soften and seem less noticeable. But in your case they are huge and are very noticeable!
philippereyniers
07-19-2008, 15:22
Very useful info !
I had dust on the sensor of my M8 very soon after I bought it. I read somewhere on the forum that the aperture mechanisms "spits" tiny spots of oil on the sensor :( Consequence : my dealer sent it back to Solms !
The M8 is a diva...
Overconfidence
07-19-2008, 15:36
Well for one thing you are missing the three HUGE spots on the first image (i raised the contrast to make them more visible).
And yes in some cases using lenses wide open so light bounces off the surface of the rear element, will cause the spots to soften and seem less noticeable. But in your case they are huge and are very noticeable!
Yeah, you can tell that from looking at the f/29 image... where the spots are in fact small and annoying. There are also "huge spots" at f/11 at all of the other darkest spots. They do in fact get bigger and softer.
This is how it looks unedited:
http://img299.imageshack.us/img299/3669/img62922lb3.jpg
While you can pick them up, thankfully I don't take pictures of a plain blue sky all that often. Nevertheless, here are real life examples at f/16 and then f/8 showing that the spots pretty much disappear when you open up:
http://img236.imageshack.us/img236/5707/img1515uk1.jpg
http://img236.imageshack.us/img236/5363/img6149gi1.jpg
But either way, the f/16 dust is with the anti-dust shake and that would make me sad on a rangefinder using a 35/50mm lens and prefocusing for the street. I use f/2-4 pretty much excluslvely on my 40D so I don't care as much.
Anyway, anyone for the whole shutter/sensor issue?
I found my M8 to nor better or worse than my 1Ds II regarding dust. On both sensors there occured from time to time 'dots' that would not be blown away. - I have no idea why or what that might be. Both Canon and Leica, along with the rest of the camera business, uses carbon lubricated shutter mechanisms. That Leica's 'spits' more than competition is a theory I don't believe in.
By the way....
I looked up some of my old 6 x 6 cm slides and ran them through a scanner. Sweat was dripping down my back when I saw all those scratches and dust spots. So, the world has become a better place - regarding clean images, with digital photography after all...
photomoof
07-19-2008, 16:12
As noted due to light angles, and stray light, spots are more focused when you stop down, and at higher shutter speeds.
However if you print large they are there, and you should clean them off as much as possible.
You are right, in the first image I only see the one in the dead center, but my guess is that at 24x30, on glossy paper, I would see it easily, especially if you raised the contrast a bit.
Now of course they would be pretty easy to find/remove, since they seem to appear in the same place in all your photos.
photomoof
07-19-2008, 16:16
By the way....
I looked up some of my old 6 x 6 cm slides and ran them through a scanner. Sweat was dripping down my back when I saw all those scratches and dust spots. So, the world has become a better place - regarding clean images, with digital photography after all...
Thus the reason, when you need them long after the fact, you go to a professional drum scan.
And you did not mention the arch enemy of film, fungus, which all my friends seem to be finding on Kodachromes. Film is an animal product, and is similar to leather, as a fungus host.
Overconfidence
07-19-2008, 16:21
As noted due to light angles, and stray light, spots are more focused when you stop down, and at higher shutter speeds.
However if you print large they are there, and you should clean them off as much as possible.
You are right, in the first image I only see the one in the dead center, but my guess is that at 24x30, on glossy paper, I would see it easily, especially if you raised the contrast a bit.
Now of course they would be pretty easy to find/remove, since they seem to appear in the same place in all your photos.
Yeap, pretty much. I guess I sort of prefer the way dust/scratches work on film because it's not always the same, meaning it's not the $1500 instrument you're using that's faulty, it's the $5 roll of film. But that's not really logical thinking.
I am (excuse my noobishness) still confused about how the dust gets on the sensor in the first place... is it only during exposure (when the shutter is open and the picture is being taken) or is the sensor left bare in the body cavity with the shutter somehow open and when you change your lens, dust gets in and can stick to the sensor? I understand it may have something to do with the sensor being charged (inherent of CMOS/CCD) and that attracting the dust to it... but if the shutter is closed, then how does the dust get to the sensor? Would it then not be possible to just, like, blow out the dust that has accumulated in the body with a lens off and then put the lens on, getting rid of dust in the body?
fdigital
07-19-2008, 17:18
Yeap, pretty much. I guess I sort of prefer the way dust/scratches work on film because it's not always the same, meaning it's not the $1500 instrument you're using that's faulty, it's the $5 roll of film. But that's not really logical thinking.
I am (excuse my noobishness) still confused about how the dust gets on the sensor in the first place... is it only during exposure (when the shutter is open and the picture is being taken) or is the sensor left bare in the body cavity with the shutter somehow open and when you change your lens, dust gets in and can stick to the sensor? I understand it may have something to do with the sensor being charged (inherent of CMOS/CCD) and that attracting the dust to it... but if the shutter is closed, then how does the dust get to the sensor? Would it then not be possible to just, like, blow out the dust that has accumulated in the body with a lens off and then put the lens on, getting rid of dust in the body?
The shutter itself covers the sensor normally unless you either open it to taken a shot or activate manual sensor cleaning. What happens is that dust gets into the cavity in front of the sensor around the mirror (in an SLR) or around where the mirror would be if it were an SLR (m8). Generally whenever you change lenses you expose the cavity to dust in the air and when you close a lens on it it gets trapped in there. The other thing that happens depends on wether the body and lens is sealed or not. In the case of a body and lens with no or minimal weather sealing (eg - 40d/m8) dust can enter pretty much willy nilly through places like the card slot, usb slot, lens mount, popup flash, battery chamber etc. Specifically in the case of DSLRs, using a zoom lens creates a vacuum behind the lens where the mirror is which sucks air/dust through any cracks/crevices it can find wether that be the lens mount, the camera body/card slots or in-between the zoom/focus rings on the lens.
So that is pretty much how it gets in there. Olympus/zuiko digital lenses are generally an exception to the whole "sucking dust in like a vacuum" as they're extremely well sealed. I noticed when I first got my e-3 and 12-60 that when zooming the lens in and out, I can actually hear the seals in the lens barrel, and the air struggling to get past them.
The reason why it sticks and clings to the sensor itself is because the sensor is an electromagnetic device which tends to emit a static charge. This charge magnetizes dust particles in the vicinity which then are attracted/magnetized to the sensor. This is also why a bulb blower wont always work when trying to blow the dust off manually.
Now, ways to prevent it or minimize it:
Try to buy weather sealed bodies and lenses (sorry m8 users). The top nikon and canon lenses and bodies are pretty well sealed. The olympus e-1/e-3 are the best sealed cameras on the market, and the zuiko digital lenses are extremely well sealed as well.
Secondly try to change lenses in areas with minimum dust. For instance you wouldn't do it in a dust storm or on a windy day on a gravel track.
As far as trying to prevent it from getting into the camera thats about as much as you can do...
For a low/no risk way to try and clean it, go to your bathroom, turn the shower on (hot water) and run it for a few minutes so there's a little steam in the room. This tends to de-magnetize the airborne particles in the room (and the bathroom is the most dust free room in most houses).
After you've turned the shower off and waited a few minutes get a big bulb blower, activate manual sensor cleaning on your camera, and hold the camera, lens mount facing down at the ground, and stick the tube of the bulb blower into the lens mount. Give about 5-8 big puffs of air and then turn the camera off/mount the lens back on (closes shutter). Go outside and shoot the sky at f22 or smaller, and see if it helped.
As for the mentioned dust vibrators on the sensors of some of the new canons/nikons - basically they don't do so much. My d300 had sensor cleaning go everytime it was turned on and off, and after 3 months of using just 2 lenses, the sensor had a large amount of dust showing up above f8. My old 5d was the same, and a friend with a 40d and it's vibrating sensor cleaner has the same problem.
On the other end of the scale, the olympus "super sonic wave filter" actually is VERY effective. Silly name, but after just over a year with my E-410, there is literally NO dust on it. My E-3 also has no dust on the sensor at f22 after about a month. I've used it in the rain and on the beach as well.
So to sum up, be smart about where and when you change lenses, buy a sealed camera/lens if possible, and if you really don't want to have to worry about your digital camera being a dust magnet, buy an olympus.
I cannot imagine why this would be, sensor dust is on the sensor -- the f-stop should have no effect whatsoever! Dust is dust, it will show no matter what you do with the lens.
Sensor dust is not on the sensor; it is on the glass cover in front of the sensor. Because there is a physical distance between the sensor and the dust, aperture makes a huge difference.
fdigital
07-19-2008, 17:42
Sensor dust is not on the sensor; it is on the glass cover in front of the sensor. Because there is a physical distance between the sensor and the dust, aperture makes a huge difference.
Yep. The dust sits on the anti aliasing filter which is a thin piece of glass in front of it. Technically it's a part of the sensor itself but it still creates distance between the dust and the actual sensor itself. Having a lens wide open or say f1.2-f4 means that the dust is so out of focus it wont show - much like shooting through a wire fence at f1.4 - the fence won't show up in the picture. Shooting at f22-f32 brings the DOF closer to the sensor so it brings the dust more into focus.
Generally speaking you won't be able to see dust in pictures on an m8/5d/d3 at around f8 or wider unless you have some serious crap on the sensor.
photomoof
07-19-2008, 17:58
Well guys, I don't even vaguely agree with all this DOF dust biz, but whatever works for you. :D
Of course there are obviously other issues here that affect how the light goes around these 3-d objects sitting on the filter (if the sensor in question has one), and therefore how dense the object appears, however, I personally see all of them. Worst of all are the oil spots, which seem to maintain size, at least on the M8 I used, no matter the aperture.
My sensor on my M8 is a little on the nose regarding dust spots but they're only ever noticable in certain shots .... it takes a few seconds to clone them out so I don't bother cleaning the sensor.
One day I'll get around to doing something about it but the whole sensor cleaning thing scares me a little so I take the option of just leaving it. They've been there since I bought the camera! :p
fdigital
07-19-2008, 18:07
My sensor on my M8 is a little on the nose regarding dust spots but they're only ever noticable in certain shots .... it takes a few seconds to clone them out so I don't bother cleaning the sensor.
One day I'll get around to doing something about it but the whole sensor cleaning thing scares me a little so I take the option of just leaving it. They've been there since I bought the camera! :p
When I had a canon 30d a few years ago the very first one I bought had multiple smears on the sensor at around f16. Not just dust - literal smears of oil.
The shop replaced it straight away.
fdigital
07-19-2008, 18:20
Well guys, I don't even vaguely agree with all this DOF dust biz, but whatever works for you. :D
Of course there are obviously other issues here that affect how the light goes around these 3-d objects sitting on the filter (if the sensor in question has one), and therefore how dense the object appears, however, I personally see all of them, parallel light rays or not. Worst of all are the oil spots, which seem to maintain size, at least on the M8 I used no matter the aperture.
No you're right - it's to do with the light coming in and hitting the sensor straight on/perpendicular when it's at small apertures like f22. This casts causes the dust to cast shadows onto the sensor. When the lens is wide open the light is less concentrated and goes onto the sensor at all different angles, so the effect is diffused.
I suspect that the DOF might have a part in it as well though. I could be wrong...
I found a test of all the digital SLRs cleaning systems effectiveness... pretty interesting:
http://pixinfo.com/en/articles/ccd-dust-removal/
1) Dust on the image sensor has the same effect as if you had dust on the surface of the film. Rarely a problem with 35mm cassettes. Large Format sheet film people know about this problem. The spots are there in the image, regardless of optics.
2) Dust in the lens changes the image based on f stops. It is true that if you look closely at the two blue sky images, the one that supposedly shows no dust actually does. There is one big spot on the right center of the image that corresponds to the worst of the many spots on the second image.
Number one and two images are representative of dust specs in the lens or on the lens.
Those dust specks would look identical if the dust were on the digital image sensor (or on the film)
Furthermore, cleaning the image sensor is not for the faint of heart. Using incorrect brushes or blowing dirt in a way that scratches the surface of the sensor can ruin a digital camera. Have any of you considered the replacement cost for a "SORRY but your handling of the sensor damaged it... No Warrantly coverage!" M8 sensor.
Highway 61
07-20-2008, 04:18
Another nice mystifying issue.
Best thing is to just not think of that dust spots/stains problem unless you are that exceptional photographer who shoots artwork masterpieces everytime you depress your digital camera shutter button.
If you are one of the average photographers around occasionally taking an excellent photo from time to time, well, PhotoShop will get you rid of the dust /dirt spots for this very photograph after a 10 minutes job in front of your monitor.
Option 1 should get you in a very bad mood OTOH chances that you obbey the Option 2 rules are 99.99%.
And if you are in a mix between Option 1 and Option 2, you're one of the Eclipse and Sensor Swabs manufacturers potential customers.
Till the Apocalypse settles in.
:D
I find the 'Arctic Butterfly' a very usefull tool to clean my 20D's sensor whenever I can't stand the dust anymore. It's a nylon brush that gets a static charge by spinning it around with the built-in motor, and it brushes off the dust particles from your sensor quite effectively. It should work on an M8 too.
Light on your path,
Dirk
Thus the reason, when you need them long after the fact, you go to a professional drum scan.
And you did not mention the arch enemy of film, fungus, which all my friends seem to be finding on Kodachromes. Film is an animal product, and is similar to leather, as a fungus host.
I don't seem to have fungis on my films,- I have films from my own production which is 40 years old, and inherited films close to 100. I think it is a climate thing, this fungis. Although, the climate in, say, NY and Oslo are very similar. Possibly with higher humidity in NY, generally, and higher summer temperatures.
I had all my films scanned to 'Kodak CD-scan', but they don't offer that service anymore. - Which contributed to their downfall, I am sure. I have bought 2. hand this Nikon 8000 ED monster and have found out that 'scanning' has a steep learning curve. And I don't have all that time and lust to dig myself down in all that software related stuff to be a good 'scanner'. For the price of the scanner I could have bought a hell of a lot of scanning from a pro. - Far more than I have scanned so far....
photomoof
07-20-2008, 05:25
I had all my films scanned to 'Kodak CD-scan', but they don't offer that service anymore. - Which contributed to their downfall, I am sure. I have bought 2. hand this Nikon 8000 ED monster and have found out that 'scanning' has a steep learning curve. And I don't have all that time and lust to dig myself down in all that software related stuff to be a good 'scanner'. For the price of the scanner I could have bought a hell of a lot of scanning from a pro. - Far more than I have scanned so far....
I still have a number of those CDs. They were not the highest resolution, but they were sharp scans, and very clean, since they were scanned as the film came off the processor.
Most pro labs will still make a high quality CD as a "proof sheet." I have had several made lately as I work my way back to using some film. I am pretty set on buying a 4x5 Wista rangefinder, but have just not made the plunge yet, since 6x9 seems more practical.
As I mentioned elsewhere (probably as a different "self") a friend just finished a book and I had a chance to look the drum scans, which made me realize no matter what I do, I cannot match them myself. So if I move seriously back to film, I will have CDs made for proofing and have drum scans made for prints I want to show. I would doubt I would ever make more than 30 in a year, and in fact that would be too many for a show, unless by some miracle the world stops spinning and I was asked to have a show at the MOMA.
Highway 61
07-20-2008, 06:48
As I mentioned elsewhere (probably as a different "self") a friend just finished a book and I had a chance to look the drum scans, which made me realize no matter what I do, I cannot match them myself. So if I move seriously back to film, I will have CDs made for proofing and have drum scans made for prints I want to show.
AFAIK drum scanners used to leave a paraffin layer behind on the film. Not a good thing if you are after that fungus issue.
Back in the 1980's I had many of my Kodachromes and Ektachromes published in journals and they went through the professional drum scanner process. I got most of my slides back in a terrible condition because of that pesky sticky paraffin layer everywhere on the slides.
At home I have a Minolta Dual Scan II scanner which I bought off eBay for peanuts last year. 2820 dpi is enough for my needs. No anti-dust software, which is not a bad thing, because cleaning the TIFF files with PS is easy and fast. A quick blast of compressed air on the slide before scanning gets most of the dust away.
@Olsen : scanning doesn't require that you know something special, it is all about how digital imaging works. If you know how RAW files work out and how to tweak a 16bits RGB file before converting it into a portable Jpeg file you're done.
Although some people say something different I have found that scanning my 35mm slides as 16bits RGB files at 2820 dpi without any image setting through the scanner software, then tweaking the file with PhotoShop later, works very well.
The outcome leaves you with two files, a clean and post-processed TIFF for your personal archives and printing eventually, and a sharp and lightweight Jpeg copy for web sharing.
Here is a Kodachrome 25 shot back in 1993 and recently scanned with this little shoebox scanner following the method above.
Stuff used was a trivial Nikon F2 and 105/2.5 Nikkor outfit.
http://www.rangefinderforum.com/forums/attachment.php?attachmentid=61804&stc=1&d=1216561499
photomoof
07-20-2008, 14:35
AFAIK drum scanners used to leave a paraffin layer behind on the film. Not a good thing if you are after that fungus issue.
Back in the 1980's I had many of my Kodachromes and Ektachromes published in journals and they went through the professional drum scanner process. I got most of my slides back in a terrible condition because of that pesky sticky paraffin layer everywhere on the slides.
At home I have a Minolta Dual Scan II scanner which I bought off eBay for peanuts last year. 2820 dpi is enough for my needs. No anti-dust software, which is not a bad thing, because cleaning the TIFF files with PS is easy and fast. A quick blast of compressed air on the slide before scanning gets most of the dust away.
I have a Minolta Dual Scan III myself, and it's not bad, and was cheap. At the time the missing Digital Ice seemed a drawback, but DI has turned out in retrospect to not be of much use except for quick and dirty work.
I have seen bad oil used on drum scans, but frankly once the scan is made I consider the original as pretty unimportant. Although it would be preferable to get them back in better condition. The ones I looked at recently were however clean. In one lifetime, I am unlikely to scan twice, nobody likes me that much. :D
victoriapio
07-20-2008, 15:18
I find the 'Arctic Butterfly' a very usefull tool to clean my 20D's sensor whenever I can't stand the dust anymore. It's a nylon brush that gets a static charge by spinning it around with the built-in motor, and it brushes off the dust particles from your sensor quite effectively. It should work on an M8 too.
Light on your path,
Dirk
Get my sunglasses out Dirk :D Yes Dirk is right, no one needs to be afraid of cleaning their sensor. Get the Visible Dust or any other good sensor cleaning system and clean them. Takes under a minute for the Leica or DSLR.
O.C.
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