5D Mark 3 auto focus problem.

[w15938713330]

I probably shudl post my question on lens section but i cant find the section anywhere.

Here is the thing , I bought a used 24-70 2.8L USM online, tne seller claimed that he tested the functionality and no problem upon mailing the lens.

However I run into some issuses.

1)When I use AF, the lens is consistently focusing in front and back without actually taking the picture.Pictures shot by MF is normal and working normally.
2) The eyecup vision is extremely dark through the lens.I can barely see the object through the eyecup.

I tried with different lens(24-105mm) but non of the problem occurred(Using exact camera setting). Since i am a beginner , is this issue about my camear, or i should try to fix the lens. How can i reslove those two problems.

[rs-eos]

Sounds like the lens is bad, unfortunately.  Especially since you tried a different lens and it was a-ok on your camera.

[w15938713330]

so it's not my camaera or setting ?

[RobertTheFat]

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@w15938713330 wrote:

I probably shudl post my question on lens section but i cant find the section anywhere.

Here is the thing , I bought a used 24-70 2.8L USM online, tne seller claimed that he tested the functionality and no problem upon mailing the lens.

However I run into some issuses.

1)When I use AF, the lens is consistently focusing in front and back without actually taking the picture.Pictures shot by MF is normal and working normally.
2) The eyecup vision is extremely dark through the lens.I can barely see the object through the eyecup.

I tried with different lens(24-105mm) but non of the problem occurred(Using exact camera setting). Since i am a beginner , is this issue about my camear, or i should try to fix the lens. How can i reslove those two problems.

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The lens should stay at maximum aperture until you press the shutter button, at which time it should automatically stop down to the desired aperture to take the picture. This allows the camera to use the lens's maximum aperture for previewing and focusing. It sounds like that's not working in your lens. Both the inconsistent focusing and the dim viewfinder point to that as the problem.

I'm afraid you've learned a possibly expensive, but ultimately valuable, lesson: A beginner should never buy a used lens.

[w15938713330]

Fair point, thanks for the informative and professional reply !

May I ask , in your opinon, is this worth to fix it ? should i just return the lens?

[Waddizzle]

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@w15938713330 wrote:

Fair point, thanks for the informative and professional reply !

May I ask , in your opinon, is this worth to fix it ? should i just return the lens?

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Return it, ASAP.  While there is still time.

[rs-eos]

I would recommend returning it. Especially if you're able to get a full refund.

[wq9nsc · Accepted solution]

Definitely return it and make sure you follow all of the "rules" if this is from ebay or another online auction site to avoid problems.  Although the aperture petals MAY have gotten stuck during shipping, it is likely this problem was known before it was sold so don't expect the seller to necessarily be gracious in accepting the return.  A stuck aperture is not uncommon on a lens that has been left to sit for a very long period of time but once it happens the only way to be confident it won't be an ongoing issue is to have it properly serviced and since this is far from a "rare" lens it would be best to return it and get a good working copy.

Rodger

[MikeSowsun]

Yes, return the lens. Even if the aperture blades were damaged in shipping, it is not your fault and the lens should be returned for a full refund.

Often in cases like this, the seller will try and reach a compromise and offer you a partial refund if you keep the lens.  Canon might be able to repair the lens, but it may cost anywhere from $200-$500, so keep that in mind if the seller offers a partial refund. 

[ebiggs1]

"Often in cases like this, the seller will try and reach a compromise and offer you a partial refund if you keep the lens."

This is not a bad idea.  If you can get the price right, a trip to Canon would yield you almost a new lens. Canon will go completely through it and bring it back to new spec.  Worth a try or offer.