Image problems with my 6D...diagonal line

Question

Hello, my name is Lindy and I'm new to this forum. I've been having a problem with my Canon 6D which results in some of my images appearing with a dark diagonal line across the upper left hand corner. I've seen this problem with both my 100mm L lens and my 16-35mm lens. Has anyone had this problem before or have any idea of what may be wrong?
Thanks!!
Solved!
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Answer 1

Hi Lindy.  You've got a bit of "dust" on your sensor (only in your case it looks like a tiny hair).  
It's easily fixed.
See page 279 of your owner's manual which describges how to clean the sensor.  
I do, however, recommend that before doing an automatic cleaning cycle, you remove the lens and point it at the ground -- that way this little hair has someplace to go when it falls... other than finding itself another location inside your camera.
After cleaning, poing the camera a plain white wall (or ceiling) and snap a photo (it doesn't even have to be in focus).  The dust shows up better at high f-stops (it'll be fuzzier at low f-stops).
Sometimes automatic cleaning is not enough and you have to do something further.  If that's the case, then see page 283 for "manual sensor cleaning".  This simply causes the camera to power down the sensor, but open the shutter (and hold it open) so that you can inspect and clean it.  If you look inside, what you're REALLY seeing are the two filters in front of the sensor.  The front filter is the one that vibrates (using a piezoelectric effect) to "shake" dust loose.  
I use a variety of techniques... the simplest and safest is to use a simple hand-squeeze (bulb) blower such as a Giottos Rocket Blower.  I recommend you not use cans of compressed air because the liquid propellant in the cans can spray out if the can is either shaken or not held perfectly level and that leaves a residue on the filter (and the only way to get that off is to wet-clean the filter).  Even air-compressors spray water and oil.  A hand-squeezed blower is the safest option.
If that doesn't work, I use an extremely soft small paintbrush.  They actually do make brushes that plug in to release any static charge so that if something is sticking because of static cling it will hopefully release.
If that doesn't work, I use a sensor scope to inspect my sensor and get a better understanding of why it still wont come free (because generally it would have by now) and then wet-clean the sensor using Photographic Solutions brand "Sensor Swabs" and "Eclipse" cleaning solution.  The solution is nearly pure methenol which means it evaporates very quickly and leaves no residue behind.
My guess is a simple manual cleaning (with camera pointing at the ground) -or- a hand-squeezed blower will likely do the trick.  If you do resort to a brush, give that brush a couple of good solid whacks on the edge of a desk or table to throw off any dust that could be on the brush -- as you don't want to add dust on to the sensor as you are trying to brush that hair away.
Most "real" camera stores (stores in business primarily to sell and service camera gear -- not big box stores that also happen to sell cameras) offer sensor cleaning, but usually there's a charge associated with that.  It's fairly easy to learn to clean the sensor (which is why Canon has a section in the owner's manual) and it's something photographers have to do.... just occasionally.
Tim Campbell
5D II, 5D III, 60Da