Dark ring in photo [duplicate]

Question

In the left corner of all my photos have always have a dark ring. I've tried wiping the lens glass but still there. Do you guys think I need my camera body or lens cleaned or both?

Answer 1

It seems likely that there is a hair, eyelash, or other small artifact on the sensor. Something on the lens is unlikely to show up like this (it'd be too out of focus). You may be able to simply blow it off — don't use your mouth, and definitely don't use compressed air, but a quality "rocket blower" (with an intake filter) should do it. Put your camera into sensor cleaning mode and give it a try.

If that doesn't work, try the more advanced methods outlined at What is the best way to clean the sensor on a digital SLR?.

You could pay to have the sensor cleaned, but it's also easy to do yourself. While you should certainly be careful, don't stress too much about damaging the sensor. It's actually protected by a glass filter, and if you use appropriately gentle methods, you won't scratch it.

Answer 2

A mark this noticeable would have to be on either the rear element, or more likely, the sensor, as was said in another answer. Dust is most harmful to image quality at locations within the optical system where the image is "created" and projected; the rear element of the lens and the sensor respectively.

Light is more tightly converged at these locations, which results in a more defined image (a shadow) of dust being presented. Think of it this way; if you aim a flashlight against a wall and put a pencil between the wall and the light, a shadow is created. The closer that pencil gets to the wall (the plane you are projecting light onto), the more well-defined the pencil's shadow becomes. At a greater distance from the wall though, the pencil's shadow is largely inconsequential with respect to how light hits the wall.

Of course, the optical system of a camera is far more complex than this, but it gives a basic idea of how a piece of dust between the sensor and the rear element can project a shadow which diminishes image quality.