Digital cameras, spots on the sensor?

Lowell,<br><br>I think that you solved the problem, but as explanation for the observation that the spots appeared to be transparent, allowing the sky to show through, I offer the following. Often in optics dust will be essentially invisible if the dust lies on the objective lens. They are too far from the focused field and are blurred into oblivion. But if the dust lies within the lens or near the aperature stop, they might show up. The fact that you saw spots in the same position, suggests that they were dust, seen slightly blurred and out of focus, and were different sizes in different shots because the lens was set at a different focal plane when the shots were taken. Is my guess correct that the dust lie on one of the rear lens elements rather than on the front?<br><br>Alan

Good points, Alan. I'm not sure where the dust may have been. My assumption was that it may have been on the digital sensor itself, not on the lens. I handled the problem as though that was the case (by blowing air on the sensor as recommended in the camera's user manual).<br><br>Dust on the sensor is equivalent to contamination on a roll of film, except that it can affect every photo, not just one. Rollei cameras (my first film camera was a Rollei 35T) were famous for "Rollei Flecks" which I believe were caused by some sort of coating on the inside of the camera which deteriorated and showed up as black flecks on random pictures. <br><br>I would expect dust on the sensor to be consistent in location and size, and unaffected by the focal length. That's not exactly what I observed (of course my expectations could be wrong), so I'm not positive that was my problem.

Lowell:<br><br>i only briefly glanced over this thread. perhaps the following links may help:<br><br> www.bythom.com/cleaning.htm
www.ultimateslr.com/clean-image-sensor.php