Odd Sensor Blemish on Canon 40D

Has anyone seen a blemish like this on their sensors? Appears to be in the same

spot regardless of composition leading me to suspect it is not lens related.

Any suggestions?<div></div>

You need to clean your sensor. You need to get a wet sensor cleaning tool. Search the archives - this is one of the most asked questions here. It's not a big deal to do it yourself - you will be very anxious when you do this the first time, but pretty soon it becomes routine.

Not a blemish, sensor dust. Good place to read and learn to clean is Copperhill. http://www.copperhillimages.com/

 

The in-camera dust cleaning system is not perfect and you probably will still have to do manual cleaning.

I'm puzzled though by the perfect circle. I would have suspected a dust spot would be more irregular and more pronounced instead of translucent. Am I wrong?

OK I see now. It's the shadow of the dust isn't it. And at smaller aperatures it becomes more translucent. Thanks guys.

You may not need to go all the way to a wet cleaning system. I'd try the "rocket blower" technique that Canon recommends. If that doesn't work, I'd next get a "static" brush (ex. http://www.visibledust.com/ ), and only if that doesn't work get into the "pads and fluid" techniques.

 

FWIW, I'm a big fan of the Copperhill folks. I have their original Eclipse and PEC-Pads kit, but I only use it about once a year - the rest of the time my Sensor-Brush does the job with much less worry (and I clean my sensor/filter frequently - as often as every day when I'm on an assigment).