In spite of the amazing advances in technology over the years, one thing remains stubbornly in place – dust. Despite our best endeavours, dust will come to plague you every now and again. Dust is also clever; it knows how to strike for maximum effect – have you ever noticed how it always appears in an important part of a picture?
Once dust is present on a camera sensor (actually it’s on the low-pass filter not the sensor – see right) it can remain there for quite a while – in one of the examples shown here, the identical blemish was present for more than 450 frames, shot over a period of a month.
Where can this dust be?
There are a number of places where dust can be a problem:
1. On the low-pass filter.
2. On the rear lens element.
3. On the lens front element.
4. Inside the lens groups.
5. On the camera mirror.
6. On the focus screen.
7. On the user’s spectacles!
Varying methods are used to rectify the problem.
How does it get there?
1. While changing lenses.
2. From the rear lens element if the lens has been left uncapped.
3. Dust can be sucked into spaces inside the lens/camera when temperature changes occur.
4. Dust can be sucked into the system by the pumping action of a zoom lens or, much worse, bellows.
5. Dust can be transferred from lens caps onto the optical surfaces, especially if you store a cap in your pocket.
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