Canon 17-55 vs Sigma 55-200 Issue

Hi,

I am using Canon Xti with Canon 17-55 IS 2.8 and Speedlite 580 EX II. When I take images with this setup they seem to come out underexposed. I tried to compare this with my Sigma 55-200 lens and Images come out much brighter. I compared them on Manual setting using same settings on the camera and flash (ETTL) and both lenses at 55mm. What gives? My camera is set to 1/160 w/ f5.6.

Thanks.

Seems very strange... could you post a couple of test pics? It would make diagnosis a bit easier.

I know my wife is going to kill me for posting these but these are the best examples I have right now.

Both are taken from the same distance at ISO 100, 1/160 sec, and F/5.6. Both lenses were at 55mm. Center point focus was used with auto WB.

Darker one is from Canon 17-55 IS 2.8.

Image from Sigma also seems a bit more zoomed in.

Thanks.

The sigma 24-70 I owned was brighter than the kit lens in ambient as well. Haven't compared images taken with a flash though.

Are there mirrors or shiny things around that may have fooled the eTTL thus under exposing the image?

(pure conjecture here) In the brighter shot, the subject takes up more space than the wall (with the wall being quite a bit lighter than the subject), so the meter (trying to make everything 18% grey) will use more flash power than the darker shot (where the subject is smaller in the frame)

This is where it would be nice if the flash power used (as determined by E-TTL) was stored in the EXIF.

Try just taking a picture of the wall with both lenses and see what you get.

Thanks guys. What I don't get is why Sigma shows more zommed in while both are at 55mm. I have tried other ranges on my 17-55 as well and almost all show darker unless I an really close to the subject. For some reason when using external flash with this lens it is under exposing.

(Removing images before I get killed)

Some Canon lenses supply data to the flash for ETTL II exposure calculations. The Sigma doesn't.

Try switching custom function for flash exposure from Evaluative to Average.