Help needed: overexposed pictures with EOS 550D and Sigma 18-50 1:2.8 DC EX

[dpiol]

<p>Hello<br>

I have an issue I recently noticed on my hiking vacation in the swiss alps. Some time ago I replaced my Canon EOS 20D with the new 550D... very happy so far. I kept both my lenses, one of them is the Sigma 18-50 / 1:2,8 / DC EX. I never had a problem with the 20D.<br>

Now, when I take some pictures at excellent light conditions (very sunny!), some pictures are completely overexposed. If you compare the 2 attached pictures, both are taken at the same time in automatic mode (P) with the Sigma lens:<br>

Taken with: Canon EOS 550D and Sigma 18-50 / 1:2.8 / DC EX<br>

overexposed picture: focal length: 38<br /> exposure time: 1/640 sec<br /> aperture: f/9<br>

good picture: focal length: 50<br /> exposure time: 1/640 sec<br /> aperture: f/9<br>

<img src="http://g4.img-dpreview.com/B0E8D883793B458C9F3369A39046108A.jpg" alt="" /><br>

<img src="http://g1.img-dpreview.com/58EA2FBF184C402B9D308F69169C615F.jpg" alt="" /><br>

Exposure and aperture are the same, so I suspect an issue with the lens (some kind of partial incompatibility?)<br>

Also I am pretty sure that I never noticed such a tremendous overexposure with my other lens (Canon 55-250 / 1:4-5,6 / IS).<br>

Anybody has a more precise idea what is going on here ?<br>

Thanks for any help<br /> Domenico</p>

 

[bobatkins]

<p>Probably the lens diaphragm (iris) is sticking open at times and it needs to be sent in for adjustment and/or repair.</p>

[cabbiinc]

<p>While I suspect that Bob Atkins is spot on I have to ask, do all of the overexposed images come from the wider end of the lens?</p>

[savagesax]

Looks like you had a great hike! I've never been there, but I'd like to one day. I'm glad you had a chance to have some fun.

 

Bob and Dan offer great advice. If this were happening on all of your lenses it would be a body issue.

 

I'm not sure about this, maybe Bob or Dan can answer this for me. Can the contacts with the lens or lenses cause this?

[wgpinc]

<p>I'm betting you have the Exposure Compensation on the 550D ratcheted way over to the plus side. Different camera, different control arrangement. Check it out.</p>

[mike_oflaherty]

<p>How are you metering the picture? Spot, partial or evaluative. I have found through trial and a lot of error. If you are using spot you can blow out a picture with little or no effort.</p>