I have had my Nikon D700 for only 6 months and found that I had to clean the sensor. I am no stranger to this task having cleaned my D80 sensor many times.
However, this particular forage into the world of cleaning was to turn out to be very expensive experience.
I always use a blower to see if the dust and and strange matter will come away from the unit before I ever delve into it with any other method. The dust just seemed to get moved around and despite holding the camera upside down while blowing, nothing seemed to budge - particularly, the edge of the sensor seemed to be heavily populated with dust particles.
So I resorted to swabs. The proper swabs and the proper liquid, together with a sensor loupe to see what was going on. Having used a few swabs the sensor gradually became clearer - one more swab should do it. Then on the last swipe a thin line appeared across the centre of the field of view - left to right
I looked with disbelief and thought that something had smeared across the sensor, so I tried again with no luck in removing it. My heart obviously sunk as I thought that perhaps I may have scratched the filter in front of the sensor.
So the camera was sent to Nikon.
The diagnosis was that the sensor was scratched. So I challenged them and said "Surely you mean the filter on the front", thinking that some grain had got into the camera and caused the problem. No, apparently the sensor underneath the filter had a very thin scratch mark left to right across the sensor.
The bill will come to in excess of £1000 with labour and VAT.
So my ultimate question is, to anyone that can answer this - How does a sensor get scratched when something is lying over the top of it and when you use full length swabs to clean the sensor?" How on earth can you scratch something that should be protected with a flat filter plate? Nikon were reluctant to suggest how it could have happened, just that there was a scratch on the sensor. But, I need to understand how these are constructed and how a full length scratch can appear underneath a low-pass filter.
In addition, and something for people to think hard about. The low-pass filter units on the Nikon D700 sensors cannot be replaced on their own...they come as a unit, and the unit is the sensor which costs £770. Could anyone advise whether Cannon low-pass filters can be replaced without replacing the sensor....because if they can, I feel a change of manufacturer coming on!