troubleshooting - Black dots appear in photos

First off, I understand that there is another thread with a similar question but mine is slightly different. I have a Nikon D80 and all of a sudden these black dots appeared on my photos. Quick google search led me to believe that there was dust on the image sensor, so I purchased a blower and tried my luck. However, while cleaning and testing I found that the specs disappeared when I removed the lens. For example,

This is the image without the lens

This is the image with the lens and with the black dots (taken at f/22)

Does this mean the problem is with the lens or still with the sensor? The black dots are most prominent at narrow apertures like f/22 so I suppose that maybe they are still there when the lens is removed but they're just not visible. I just want to confirm so I know exactly what the problem is and accordingly try to fix it.

Sorry for the long post, and thanks in advance.

Answer

Dust in a DSLR generally ends up on top of a thin layer of glass(like) above the sensor, usually an anti-alias filter. Even on cameras without AA filters there is still usually a layer of glass (or similar) there.

This means the dust is slightly above the sensor.

When you expose with a lens set to a high (small) aperture, this near-point-source casts a very sharp shadow from the dust on the sensor and you see it.

WIth a wide aperture (or no lens at all) the light is coming from a wide source, and so casts a diffuse shadow which might not be visible at all.

It is like your hand at waist height casting a shadow in the sun, but with diffuse light from a cloud, it casts no shadow -- doesn't mean it isn't there, just how the shadow falls.

If there were no glass above the sensor, the dust would almost always show up, just as your hand would cast a shadow even in clouds if held an inch above the ground.

It's dust. Clean it, have it cleaned, or if you mostly show with wider apertures it will not be noticeable. All DSLR's get it. You can reduce how quickly by taking care when changing lenses, but they will will get dusty eventually.

Dust on the lens front or back reduces contrast but generally will never appear as a clear spec on the image (it is so completely out of focus, much as you cannot see a fence with the lens pushed up against it, but the fence color bleeds through). Dots on the image are almost always on the sensor not the lens in any normal situation.