The dust particle that occupied my mind

Problem

Using my Nikon D40 I took some pictures and in all of them I could see a spot in the middle.

I could see a spot both (a) when looking through the view-finder and (b) in the final picture. Haven't found out how to get rid of the spot on the view-finder but will tell how to do that if its caused by some dust particle on the sensor.

Testing for dust particles on the sensor

This is what I read on the internet. I don't remember the exact advise and reasoning but this is essentially what I did after reading that page.

(1) Set the focal length to maximum.
(2) Set the aperture to minimum.
(3) Set the focus (manual) completely off.
(4) Take a picture of a blank white sheet.
(5) Look at the picture and check for black/grey spots.

In my case, I could anyway see the spot in the final pictures, but when I did this then the spot was more prominent.

The solution: Blow air and clean the sensor/filter

Long story short here is how the spot in the final picture was removed.

(1) Things needed - Camera, air blower, enough light to look at the sensor/filter area.
(2) Better to have a fully charged battery.
(3) Remove the lens from the camera body.
(4) Turn the camera on and from the setup menu set the "Mirror lock-up" option to "On".
(5) Set the camera mode to manual.
(6) Change the shutter speed till you reach the "Bulb" mode.
(7) Now press the shutter button and keep it pressed.
(8) The mirror will give way to the sensor/filter area.
(9) Look at the sensor/filter surface. In my case I could clearly see a speck of dust in the center of the surface.
(10) Use the air blower and blow air on the sensor/filter area while holding the camera upside down (so that dust can easily fall vertically down).
(11) Release the shutter button.
(12) Switch the camera off.
(13) Put back the lens, take some pictures and see if it helped.

Happy clicking.