Is it sensor damage? Or dust?

Question

I have been trying to shoot partial solar eclipse today with my Nikon D3100, and later noticed this spot on images:

http://pix.academ.org/img/2011/01/04/70baea815d1557594f096a82ab05704f.png

I do not have special sun filter, but i tried my best to cover lens with disk from old 3.5" diskette. So now I'm unsure - did I damage my sensor? Or is it dust? Sensor cleaning function doesn't help and i haven't changed lens since i bought the camera.

Answer 1

That looks like a typical dust spot.

How blurry the spot is depends on the distance between the filter in front of the sensor and the actual sensor (which is constant for each camera model), and the aperture used. For a smaller aperture (higher f-number) the spot gets sharper.

The sensor cleaning function may remove some dust, but I read a test a while back that showed that sensor cleaning functions varied from pretty weak to completely useless...

Answer 2

You can try this:

• step down at max (eg. > f/22)
• take an off-focus blurry picture of some uniform surface (eg. ceiling or monochrome wall). Best is when you can get rid of the subject grain itself, so look for slow exposures and manual out-of-focus!

If the sensor is dusty you'll clearly notice spots. If you have scratches, you'll see them also.

For your second question, I guess that such low-level electronics works or not. You'd get burnt photosensors that would show as pixels anyway, probably not blurred spots.