Dust on Sensor Question

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SBurkholder

SBurkholder

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I was out shooting at a Hawk Watch site over the weekend with my Z6. When I got back to look at the images I noticed that when I shot stills, my images were fine. But when I shot movies, they all came back horribly dusty and spotted with even a hair showing. So I've spent most of the day trying to figure out what was going on. Without going into the detail about all the combinations of lenses, TC's that I tried I finally found my answer as to the cause, and that was the aperture setting. When I was shooting stills, my aperture was typically as open as the lens would allow or close to it. Because it was a sunny day and shutter speed was set at 1/50, for the film portion of shooting, I was typically at the smallest aperture available to me.
So I discovered that at small apertures, sensor dust shows up on the image and at large apertures it isn't noticeable. My question is why? Why would the aperture cause such a huge difference in image quality? When cleaning sensors, it seems that you should take review images only with the lens stopped down? Am I the only person who didn't know this?
 
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Thanks Rassie. I didn't realize that there was a filter placed on the sensor. It begins to make sense now. I'm really surprised by the amount of difference that shows up on the image though. Looks like I'll be cleaning the sensor more often, or at least testing it prior to major shoots.
 
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Some folks make it a habit to blow the sensor with a rocket blower after every shoot before they put the camera away. I also use the rocket blower more often lately than I used to before. It does seem to keep the sensor cleaner.
 
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Sensor hygiene. I don't swap lenses if the environment is very dusty. Make sure camera is turned off when swapping lenses, always carry and use a rocket blower and use it when changing a lease. Set yourself up with lens end caps loosened and ready to go to minimise the time the camera is without a lens. Hold camera face down (sensor down)
I used to get dust problems, since adopting this policy I have had none......and I do check at f22 and above
 
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Ian said:
Sensor hygiene. I don't swap lenses if the environment is very dusty. Make sure camera is turned off when swapping lenses, always carry and use a rocket blower and use it when changing a lease. Set yourself up with lens end caps loosened and ready to go to minimise the time the camera is without a lens. Hold camera face down (sensor down)
I used to get dust problems, since adopting this policy I have had none......and I do check at f22 and above
Click to expand...

Yes, fully agree. But if the malheur happened and there is something you can't blow off you may consider using one of these Eyelead Gel Sticks. I tested it first time with my good old D600 some years ago. It was one of the series that had this pollution problem caused by the shutter mechanics. Although it felt a bit strange in the beginning to take something and deliberately touch the sensor with it, it worked perfect.
 
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If you stick with apertures of f/8 or larger the dust is not likely to be visible in the images. When doing a sensor cleaning I take shots of the sky with a f/16 aperture so that all the specs show up and I know where to clean.

Outdoors I put the teleconverter on the camera body first and then can take longer to attach it to the prime lens. I have two D850 cameras which provides me with a backup camera and also greatly reduces lens changes in the field. If it is windy I will go inside my car or a building to make lens changes while traveling.
 
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SBurkholder said:
So I discovered that at small apertures, sensor dust shows up on the image and at large apertures it isn't noticeable. My question is why? Why would the aperture cause such a huge difference in image quality?
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The why is that stopping down the lens to a smaller aperture collimates the light making it far more directional allowing the dust spots to cast dark shadows on the sensor. At wider apertures the light hits the dust spots and the sensor at a wider range of angles which still degrades micro contrast in that area of the sensor but often doesn't show up as obvious dark spots unless the dust is particularly large. It's analogous to how your body will cast a very dark, hard edged shadow in bright directional sunlight, a softer shadow when there's soft high clouds diffusing the light and often you won't see a shadow at all when it's still bright but there's additional cloud cover further diffusing the light such that it comes down from a wider range of angles and is not such a distinct collimated beam of light.

One big take away is that you should stop your lens way down when testing for sensor dust or hairs. I'll generally mount the 70-200mm or 300mm lens, point the camera at a patch of blue Northern sky and stop down to at least f/16 if not f/22 to take test shots and then inspect them at 100% view for the telltale dark spots or dark wavy lines left by dust spots or hairs.
 
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Rassie said:
You're correct. Dirt on the sensor shows up better at small aperture settings compared to wide open ones. I knew about this, then forgot about it, and was made painfully aware of it again when I stopped down to around F13 for a landscape shot some time ago.

Here's an explanation: https://photographylife.com/why-sensor-dust-is-more-visible-at-small-apertures#:~:text=Because the angle is more or less straight,,for sending the illustration! Subscribe to Our Newsletter
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Hello Rassie,
Tmac here I'm new to the fold . Thanks for all the info on sensor cleaning and good practice around this subject in the field. Reading
all the questions and answers since I've joined has taught me a lot.
Thanks again
Tmac
 
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Ian said:
Sensor hygiene. I don't swap lenses if the environment is very dusty. Make sure camera is turned off when swapping lenses, always carry and use a rocket blower and use it when changing a lease. Set yourself up with lens end caps loosened and ready to go to minimise the time the camera is without a lens. Hold camera face down (sensor down)
I used to get dust problems, since adopting this policy I have had none......and I do check at f22 and above
Click to expand...
Right on ... as recommended by my camera dealer and pro wildlife photographer ... I also follow his recommendation to blow once around the lens camera body connection before removing the body and immediately putting it on the ready and waiting new lens. I have not changed a lens outdoors in a long time. I do the changes indoors or inside a vehicle but being a wildlife photographer and frequently set up with 2 or 3 bodies with different lenses on them I do not have that need.
 
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Two good pieces on sensor cleaning...
A staged approach may mean you never have to swab.
www.lensrentals.com

Guide to Cleaning Your Camera Sensor

A fair amount of unease comes with interacting with one of the most fragile parts of a digital camera. Automatic sensor cleaners help but haven’t replaced the need for sensor cleaning entirely. However, cleaning camera sensors is not as delicate of an operation as it seems. You still might...
www.lensrentals.com
www.cleaningdigitalcameras.com

Cleaning Digital Cameras - guide to cleaning DSLR and Mirrorless cameras.

The Dust Patrol in Vacaville is your modern, competent, and flexible supplier for professional industrial cleaning, private residences and homes, office buildings, and for industrial manufacturers.
www.cleaningdigitalcameras.com www.cleaningdigitalcameras.com
 
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Just my 2 cents: objects on the sensor do show up much better at smaller apertures, but they're still visible at wider apertures, especially against solid backgrounds like an open sky, or a creamy bokeh. Thank goodness for spot removal in LR / ACR as well as copy/sync to all photos.
 
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Ian said:
Sensor hygiene. I don't swap lenses if the environment is very dusty. Make sure camera is turned off when swapping lenses, always carry and use a rocket blower and use it when changing a lease. Set yourself up with lens end caps loosened and ready to go to minimise the time the camera is without a lens. Hold camera face down (sensor down)
I used to get dust problems, since adopting this policy I have had none......and I do check at f22 and above
Click to expand...
I never change lenses in the field. If think I may need a different lens I bring a second camera. Have never had to clean a sensor in fifteen years of digital shooting. Maybe a little lucky also.
 
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Sometimes it's unavoidable.
Sometimes the dust is invisible and floating in the air.
Do it blind in a pillow case. Or there's a change bag with a HEPA filter.
 
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ronpier said:
I never change lenses in the field. If think I may need a different lens I bring a second camera. Have never had to clean a sensor in fifteen years of digital shooting. Maybe a little lucky also.
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I as well try to avoid it if possible and if I know I will need different focal lengths in random order I prefer to have two bodies with me, because that is still the quickest way of changeover, but certainly not the cheapest ;).
Apart from this I just try to get more practice for quick and - partly - blind lens changeover, similar to what @Steve was showing some time ago regarding blind and fast adding and detaching of a TC. The type and amount of dust is one parameter that influences the likelihood of getting the body contaminated, but I think the time the open body gets exposed to the dusty environment is just as important and htere is quite a lot that can be done just by the way how the lens changeover is executed.

Up to now it worked quite well and since the days with my D600 that was polluting its own sensor due to poor shutter construction I am happy to say that I didn't loose any pictures or have to spend extensive time in post processing due to dust spot removal.
 
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