A customer has sent me an email with a strange problem: he has seen something blurred in the viewfinder of a 6d, after which he turned off the lens, and a burned smell came out. He has 2 similar 6d cameras…. and after a certain time he had the same symptoms with the second 6d too (!).
So he has brought to me one camera, to find out what happened, and case possible, to repair it. He was thinking on an electrical short or so.
Exactly in that region of the camera there are no parts which could cause such a problem. But let we see, what happens, case you have a big aperture (small F-number) lens, and you just let your camera on a table in the sun, without a lens cap.
To understand this, let see a sketch of the optical system.
Normal focalizing to an object at infinite (long distance).
The image of the object is focalized on the CMOS plane – which is hided by the shutter, and the light beams are deflected by the main mirror towards the matt screen, the image can be seen in the viewfinder. The lens is at the shortest distance from the CMOS.
Object at a short distance – let we say, 1 meter from the camera.
To get a sharp image, you focalize the lens – so you move it to a longer distance from the CMOS.
The image will be also projected on the matte screen.
But what happens, if you leave the lens focalized to 1 meter – but you turn your camera towards the sun?
The sun is at infinite – so it’s image will be focalized to the short focal distance – but unfortunately at that point there is a black object: the mirror frame, or the shutters frame. And the melt, and produce smoke, and smell.
So the camera has only to be cleaned in the mirror box, and after this looked as on the picture below. The photo quality is not affected.
The best solution is of course changing the mirror – which operations needs a complete disassembly of the camera, the mirror box, and after assembling an AF readjustment. I would not do it even for my own camera without a service software.
So, case you are in the sun, always put on the lens cap. It’s not a joke.