Dust Bunny Question

SeagullSteve

SeagullSteve

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Steve
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I've got a couple of dust bunnies in my 7D - nothing major and I'm ok with cloning them out. I was begining to think that the bunnies were actually on the back of a lens as they are not always visible. My macro lens was my cause for concern.

I looked closely at the lens but couldn't see any dust. Then I spotted the same dust mark on a picture from my 15-85. As a result I did some tests yesterday and the dust is pictures from all my lenses, so definitely in the camera.

what has thrown me is the the bunnies change depending on the F stop. For instance on the macro at f2.8 I can't see the bunnies but at f16 they are clear. As the F stop gets smaller the dust bunnies get sharper.

So if the bunny is on the sensor why does it get sharper with the F stop. Surely if it's on the sensor itself it should always be sharp?
 
SeagullSteve said:
what has thrown me is the the bunnies change depending on the F stop. For instance on the macro at f2.8 I can't see the bunnies but at f16 they are clear. As the F stop gets smaller the dust bunnies get sharper.

So if the bunny is on the sensor why does it get sharper with the F stop. Surely if it's on the sensor itself it should always be sharp?
Click to expand...

This is perfectly normal. The dust bunnies aren't actually on the sensor they're on the low pass filter which sits just in front of it. Since the image is focused on the sensor itself the dust bunnies are unsharp - particularly so at large apertures. Stopping the lens down to smaller apertures does make the dust appear sharper due to the increased depth of focus at the sensor plane - not to be confused with depth of field, which is out in front of the lens rather than behind it.

The standard test for sensor dust is to take a shot of a plain light wall or the sky and stopped down to a very small aperture - which shows up the dust to maximum effect. You may not even see the dust when taking shots at large (wide) apertures.

I use an Arctic Butterfly brush for sensor cleaning and it works well as long as the dust hasn't become stuck (welded) in which case you'll need to try one of the wet cleaning methods.
 
This is pretty normal.

The depth of field at f16 onwards will increase the visibility of dust on the sensor (as others have said, it's not on the sensor, just on the filter in front of it) You should be fine at larger apertures.

Unfortunately, dust is just one of the things you have to deal with with an SLR. You can't get away from it no matter how much you try!
 
CT said:
The dust bunnies aren't actually on the sensor they're on the low pass filter which sits just in front of it.
Click to expand...

I didn't realise that there was a filter in front of the sensor - explains why they aren't sharp images as I would have expected.

Thanks
 
SeagullSteve said:
I didn't realise that there was a filter in front of the sensor - explains why they aren't sharp images as I would have expected.

Thanks
Click to expand...

Actually, if there wasn't that filter in front of the sensor , then sensor cleaning would be a far more dangerous thing to undertake. At least you now know you're cleaning the filter not the sensor.
 
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