Dust on Sensor
I use a DSLR. Of late, many of my photographs have a weird black mark at the top right. I initially thought that it might be some dirt on my lens, but the spot remains even after cleaning the lens. What should I do?
Chandni Nair, Kochi
Since you have already cleaned your lens, it is evident that there is nothing wrong with it. The mark that is visible in your pictures is a result of dust particles that have settled on the image sensor of your camera. To confirm that this is the cause, shoot a picture of a white wall and overexpose the image by 2 or 3 stops. The entire picture will be featureless white, but the dust marks will still be visible.
Sensor dust is particularly visible while using narrower apertures like f/11 or f/16. If the amount of sensor dust is not too much, you can remove it during post-processing. However, if you find this too cumbersome, it is time to get the sensor cleaned. First, use the Sensor Cleaning feature of your camera, if available. If the dust still remains, unmount the lens, set the camera on the Bulb mode and while the mirror is up, use an air blower. Do remember that the tip of the blower should not touch the sensor!
If this does not reduce the dust as well, it is best to avoid cleaning the sensor on your own. Give the camera to an official service centre.