Inconsistent Autofocus - EF 50mm 1.8 II

[TheBlackestShee]

I have a 5d2 and the 50mm 1.8 II. This lens has reallly inconsistent autofocus - sometimes it will nail focus, other times it will significantly front focus OR back focus.

I tested it on tripod with the center focus point, and manually changed focus before testing again. My lens kept giving inconsistent results. But when I tested my girlfriend's lens (same lens, different copy) on the same body, it nailed focus every time. I don't think my copy has always been this bad, but I'm not sure - I honestly don't use it very often.

So what gives? Anyone know why this happens? I know I can send it in for repair, but I'm more interested in why this happens. (Also not sure it's worth sending it in.) 

[TheBlackestShee]

Clarification - When I autofocus, it will seek either behind or in front of the focus point and flash focus confirmed, even though focus is definitely off.

Ask me if you have any other questions, or if I forgot anything important...

[RobertTheFat]

Have you tried your lens on your girlfriend's camera? If that lens/camera combination doesn't exhibit the problem, maybe you could just trade lenses. I know that sounds silly; but if the shoe fits, wear it.

[ebiggs1]

Odds are your lens is faulty.  A common thing for these very inexpensive lenses.

[TheBlackestShee]

Bob - Yeah, it acts on up her camera too.

ebiggs1 - I feared as much, although I thought it was odd that it was confirming focus, and it doesn't seem to make any abnormal noises/movements during autofocus. No chance it (or the bodies, or combination of) just need cleaning?

[ebiggs1]

"ebiggs1 - I feared as much, although I thought it was odd that it was confirming focus, and it doesn't seem to make any abnormal noises/movements during autofocus. No chance it (or the bodies, or combination of) just need cleaning?"

If the lens 'thinks' it is operating correctly it will show no signs or make noises out of the ordinary.  However, that is no indication it"is" working correctly.

Of course there is always a possibility it needs cleaning, no matter how slim.  Go ahead and clean the contacts with denatured alcohol.  I doubt that is the case but, hey, why not?

And of course you run in to the problem of cost if you decide to repair it or have it done.  You can buy a new one most likely cheaper than the repair bill will be.  This can be considered as a "disposable lens"!

The fact it acts up on different bodies is a pretty much dead give away.  Just make sure that is the case.

[Sisster108]

You may be to close to your subject. Try moving back and foruth to your subject. That will happen to me due to I am too close to my subject. 

Hope this helped!

Amanda 🙂