Where is the dust at?

Dust on sensors is a “fact of life” with DSLR’s
First thing to understand is if you can see the dust spots in the optical viewfinder, it is not on the sensor.


http://en.wikipedia.org/wiki/Focusing_screen
The sensor is behind the shutter.and can be seen only when the shutter is open

The spots that you are seeing when you look thru the viewfinder with the lens off are on the ground glass viewing screen and will not show up in photos. The ground glass view screen is above the mirror 5 is the bottom surface of the ground glass viewing screen and is easy to clean. Dust can also be trapped on the top surface and that is major requiring the body to be disassembled. :) It may bug the heck out of you, but it will not show up in the photographs. So most of us live with it.

4 is the location of the sensor (or film on film cameras) 3 is the shutter, which is open only when a photograph is being taken. Your instruction book should explain how to lock it open for cleaning. Be sure you have a fully charged battery, because it takes battery power to hold the shutter open.

To demonstrate how unlikely dust spots on the rear element of the lens are to show up in the viewfinder or photographs, I conducted a test by mounting a large object behind a 18 to 55 MM Zoom lens

I then took a photograph at a Focal Length of 18MM @ f4

I also could not see it on the viewscreen
Next, a photo was taken with the lens closed all the way down to the smallest aperture, increasing the depth of focus of the lens

This shows that anything that is on the rear (or the front) of the lens must be large to show up in the viewfinder or photograph and even then it will not have sharp edges. How much of a blur it will be is determined by focal length and f stop

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