Problem with sigma f/28 17-50 DC EX

[Simplewaves]

Hi I'm trying out the sigma f/2.8 DC EX 17-50mm before I buy it from a friend. I have a problem:

It's like it's stuk on 2.8. Cuase when I put the camera on say, f 11 it blows out the picture unless I keep the same shutterspeed I use when I'm at f/2.8. And the depth of field stays the same from f/2.8 to f/ 22.( super shallow)

I'm using a canon XSi. I've got the canon 18-55mm f/ 3.5-5.6 and this works fine.

Can someone please help me?

Have a nice day.

 

[Markw]

Some photos showing the problem could be in order.

Mark

 

[Simplewaves]

http://i44.tinypic.com/25kpmkx.jpg ( f/2.8 1/800 ISO 100)
http://i43.tinypic.com/mhvh8m.jpg ( f/22 1/800 ISO 100)
http://i41.tinypic.com/klsfm.jpg ( f/22 1/13 ISO 100) ( corectrly exposed in camera)
http://i43.tinypic.com/amy3xe.jpg ( f/2.8 1/100 ISO 100) ( shallow depth of field)
http://i40.tinypic.com/2mgp9bn.jpg ( f/22 1/100 ISO 100) (same DOF result)
http://i43.tinypic.com/qqbot1.jpg ( f/22 0"5 ISO 100) (corectly exposed in camera)

Sorry for all the links. Have problem uploading in the reply.

 

[Markw]

Take the lens off the camera, look through the rear element, and manually trigger the diaphragm lever (or whatever it's called that makes the aperture blades close). See if they open up when you move the lever or not, and report back. If they don't, the lens is obviously the problem (broken), and needs to be returned.

Mark

 

[analog.universe]

On Canon mount lenses, there is no aperture lever. You can test this with the lens mounted to the camera however... In Manual or Av mode, set the aperture to f/16 or f/22, and then press the depth of field preview button. (It usually on the camera body on the underside of lens mount, check your manual if you can't find it) If you look inside the lens, you should see the aperture blades stop down when you hit the DOF preview. If you don't, then there is a problem with the lens.

 

[o hey tyler]

Sounds like stuck aperture blades to meeeeeeeeeeeeeeeeeeeee.

 

[Simplewaves]

Yeah It's defently stuck blades. I pressed the DOF botun and nothing happend. How do I clean or fix these blades???

I apriciate the help.

 

[rendodge]

Any luck with that? I am having the same problem. I am not 100% sure it is stuck blades. Could be 1. disconnect between camera and aperture motor/an electronic problem. 2. the aperture motor itself. It seems to me that if it were stuck blades i would hear some sound as the lens "tried" to close the aperture hen I push the DOF preview button.