50mm 1.8 "hanging" on 5d mk III body

[bmeeks]

My 50mm 1.8 lens works fine on my old 7D, but when I try and use it with my 5D mk III it will only shoot one frame then it goes dark in the viewfinder. 

Though the viewfinder is dark (it acts just like the lens cap was on the lens), the autofocus will "hunt" when I press the shutter button halfway. But because I can't see anything through the viewfinder, it of course never catches focus. 

My other Canon lenses work just fine on the 5D Mk III body, it's only with the 50 1.8 that this is a problem. 

Any suggestions as to what might be happening?

Thanks

[Ray-uk]

It sounds like the mirror is catching on the back of the lens.

[bmeeks]

That's a possibility, but why would the mirror just do this on the 50mm and not on any other lens?

[MikeSowsun · Accepted solution]

---

@bmeeks wrote:

That's a possibility, but why would the mirror just do this on the 50mm and not on any other lens?

---

I bet you have the EF 50mm f/1.8 II with the plastic mount. This lens is known for having the plastic rear cover come loose which can then cause it to get stuck on the camera.

That piece is held in place by 4 small plastic tabs. If one or more break they can cause the cover to not sit flush with the plastic mount. If that is the case with your lens, you can pop off the cover and still use the lens. 

[bmeeks]

Yep, that's the lens I have I have. Thanks, I'll check to see if that plastic cover has come loose somehow. 

[bmeeks]

Bravo, Mike! You nailed the problem. The plastic cover had, indeed, come loose. I discovered this after a minute or two of investigation, and realized "loose" was "around" but "back and forth," meaning, there was nothing to screw in tighter, but I was able to "snap" the cover back in place with a very small amount of pressure. The plastic cover made a pleasing little "click" sound as it popped back into place. 

I put it back on the 5D Mk III and now it's working like a champ! Much appreciated.

[MikeSowsun]

You are very lucky to discover it before it caused the lens to get stuck on the camera. It has happened to many people and they often end up destroying the lens or damaging the camera's electrical contacts getting it off. 

Make a habit to inspect that cover each time you use it.

If it gives you more trouble you could just use the lens without the cover, but the inside of the lens will me more exposed.

[ebiggs1]

"Make a habit to inspect that cover each time you use it."

Sounds like a candidate for the circle file.

[wq9nsc]

If I owned one, I would definitely be putting a few drops of epoxy between that piece and its attachment point to make sure that it never came off again. 

Rodger