You've got a hair and some dust on your sensor (no doubt about it).
So the good news is... this is actually fairly normal and it's not a defect or problem with the camera. It just needs to be cleaned.
If you've got a "real" camera store that does cleanings (I would not take it to a big-box store that just happens to sell cameras) then they can probably take care of it for a reasonable fee (likely less than $50... maybe less than $25 if you're lucky).
But you can also do this yourself.
Invoke the camera's self-cleaning cycle:
1) In a clean (dust-free) environment, remove the lens and body cap. Point the camera at the floor.
2) Press the 'Menu' button and navigate to the page with the "Sensor cleaning" option (it'll be one of the pages with the yellow-wrench icons on the top tab... but you likely have a few pages of yellow-wrench tabs).
3) Invoke the "Clean now" choice (note that the camera will also usually do this on power-up or shutting down and the choice can be grayed out.)
Depending on how well this hair is stuck to your sensor... it may or may not fall free. The reason for pointing the camera at the ground is because you want it to fall "out" of the camera (if the camera were upright instead of facing down then anything falling free of the sensor would just land on the floor of the camera below the reflex mirror... and that means it could find it's way back onto the sensor again.
Put the lens back on the camera, set the camera to Aperutre priority mode... dial in a high aperture value (like f/16 or f/22) and take a photo of a plain white wall or plain blue sky (no need to focus the lens).
If the debris is still on the sensor you'll see the shadow of it in that test frame you just shot.
If it worked, celebrate.
If it didn't work, don't panic.
Now you're going to need a few supplies (if you're going to do this yourself instead of having it professionally cleaned). You'll want to pick up a tiny PRISTINELY CLEAN and VERY SOFT painbrush (they actually make special versions of these that have a grounding wire attached... designed to ground out any "static charge" that might be causing stuff to cling to the sensor.)
You should also get a HAND-SQUEEZED air blower such as a "Giottos Rocket Blower". You might be tempted to use a can of compressed air or even a home air compressor... DO NOT use an air-compressor or "canned" air. Air compressors spew oils and moisture and will probably get your sensor dirtier than when you started and also are usually entirely TOO MUCH pressure for the delicate inner parts of your camera. "Canned" air (like "Dust Off") uses a liquid propellant this stuff will leave a foggy residue on your sensor and it doesn't evaporate clean. If this happens then you'll have to use "wet" cleaning swabs such as "Eclipse" brand cleaning solution and their "Sensor Swabs" to remove the residue.
Back in the "Sensor cleaning" menu there's a choice for "Manually clean". That option simply causes the camera to swing the reflex mirror out of the way and open the shutter curtain ... and it holds it open. At this point you can use the HAND-SQEEZED air-blower to try to blow off the sensor (don't let the tip of the bulb touch the sensor ... or anything inside the camera.)
If that doesn't work, you can use the PRISTINELY CLEAN and SOFT paint brush to see if it can sweep the debris clear.
If none of the above work... then it's usually time for a "wet cleaning" method... or a "Sensor Gel Stick" (a gummy gel like thing on the end of a stick... you gently push the gummy gel to the sensor... the hair sticks to the gummy gel... and you pull it away and the sensor is now "clean".
The "wet" cleaning method uses "Eclipse" brand cleaning solution (nearly pure methanol so the alcohol-based solvent can help clean the sensor... but since it's methanol it evaporates VERY quickly and leaves virtually no residue. There are loads of tutorial videos on how to do this... but follow the instructions. You'll put just a couple of drops (as in 2 or 3... not as in 8 or 10) on the swab. You then get a single swipe from one edge of the sensor to the other (you shouldn't need to use pressure... just a gentle swipe).
Once the sensor is clean, just take care when you change lenses that you aren't in a dusty environment. Do not leave the camera body with the opening pointed up (so as to avoid things landing inside the camera). When you want to remove lens #1 and attach lens #2... get lens #2 out and ready, remove the rear dust cap. Detach lens #1... attach lens #2... THEN put the rear dust cap back on lens #1 and put it away (don't leave the body open for extended periods of time).
You can leave a lens on the body all the time... but if for some reason you don't want to store the camera with a lens attached, make sure you put the body's front dust-cap on the camera body before storing it.
I do astrophotography and we tend to get dust bunnies more often than most. That's because we take lots of VERY long exposures. When the camera shutter opens, it swings the reflex mirror out of the way and that makes a "whoosh" of air inside the camera (stirring up any dust) and then the camera shutter opens.
For most ordinary photography the shutter opens and closes so quickly that there isn't a lot of time for dust to settle on the sensor. But for astrophotography... that shutter might be open for the next 10 minutes (or more).... and the astrophotographer will take loads and loads of long exposures.
But getting dust on the sensor can (and does) happen all the time. It's fairly normal. It's something that if you're heavily into photography you probably want to learn to clean (instead of sending the camera in). There are loads of YouTube videos that will show you how to properly use the cleaning products. Don't be in a hurry. Be gentle. No aggressive rubbing/scrubbing... just soft easy swipes. Don't save the swabs. Once they've been used... toss them in the trash. Always use a pristinely clean/fresh swab each time you clean the camera.
Tim Campbell
5D III, 5D IV, 60Da
