dust on lens???

I took some photos of a waterfall today. When I looked at them on the computer, I noticed a black dot in the top left corner area of certain photos. After some thinking, I found that the dot only appeared at certain focal lengths because there were some photos where the dot was blurry and others where I could not see it at all. I cleaned the lens and took some additional photos of the sky to see if it showed up. It did! I have not seen this before and I have not removed the lens from the camera. What could this be and more importantly, where could it be. Please help!!!!!

Nathan

Nathan,

Can you post a pic for us to see? That would give us a better idea of what it is. Going off of your description, my first guess would be dust on the sensor. Check out this thread:

http://forums.photographyreview.com/...highlight=dust

Classic dust on the digital sensor symptoms... But I'm assuming you're using a digital SLR. The dust will show up more in some shots than others because of depth of field (DOF).

Wide lenses with moderate aperture (say f8) will have tons of DOF, and that DOF will be closer to including the sensor itself - that's why you'll see it more clearly. It can almost disappear in the next shot if, for example, you used a 200mm lens wide open focused at 50' or so.