Sigma EF-500 underexposure problem

I am a beginner photographer, but I'm learning: I have a Sigma EF-500 DG Super Flash, that takes pictures that are very underexposed, about 80% of the time. The pop-up flash does a better job. I've dialed in 1.5+ exposure on my Digital Rebel. I've setup a tripod and taken 10 pics of the same object, and still have the problem. Even with the exposure upped I still have to post process them up by 1 to 2 + exposure. Some are so grainy they are discarded. I've tried setting identical settings, iso, shutter, f-stop, and still get different results. The only thing I can see sometimes is that the two pics will have the same focal length (ie 55mm)in EXIF data and they don't look like they should.

Thanks for any suggestions:
Gary

EXIF data:

Underexposed pic
Model = Canon EOS DIGITAL REBEL
Orientation = top/left
X Resolution = 350
Y Resolution = 350
Resolution Unit = inch
Software = Digital Photo Professional
Date Time = 2006-12-13 21:47:30
YCbCr Positioning = centered
Exif IFD Pointer = Offset: 148

[Camera]
Exposure Time = 1/60"
F Number = F5.6
ISO Speed Ratings = 400
Exif Version = Version 2.2
Date Time Original = 2006-12-13 21:47:30
Date Time Digitized = 2006-12-13 21:47:30
Components Configuration = YCbcr
Shutter Speed Value = 5.91 TV
Aperture Value = 4.97 AV
Exposure Bias Value = +1.33EV
Max Aperture Value = F5.6
Flash = On
Focal Length = 55mm
Flashpix Version = Version 1.0
Color Space = sRGB
Exif Image Width = 2048
Exif Image Height = 3072
Focal Plane X Resolution = 3443.946
Focal Plane Y Resolution = 3442.017
Focal Plane Resolution Unit = inch
Sensing Method = One-chip color area sensor
File Source = DSC
Custom Rendered = Normal process
Exposure Mode = Auto exposure
White Balance = Auto white balance
Scene Capture Type = Normal

Exposure OK

Model = Canon EOS DIGITAL REBEL
Orientation = top/left
X Resolution = 350
Y Resolution = 350
Resolution Unit = inch
Software = Digital Photo Professional
Date Time = 2006-12-13 21:47:52
YCbCr Positioning = centered
Exif IFD Pointer = Offset: 148

[Camera]
Exposure Time = 1/60"
F Number = F5.6
ISO Speed Ratings = 400
Exif Version = Version 2.2
Date Time Original = 2006-12-13 21:47:52
Date Time Digitized = 2006-12-13 21:47:52
Components Configuration = YCbcr
Shutter Speed Value = 5.91 TV
Aperture Value = 4.97 AV
Exposure Bias Value = +1.33EV
Max Aperture Value = F5.6
Flash = On
Focal Length = 55mm
Flashpix Version = Version 1.0
Color Space = sRGB
Exif Image Width = 2048
Exif Image Height = 3072
Focal Plane X Resolution = 3443.946
Focal Plane Y Resolution = 3442.017
Focal Plane Resolution Unit = inch
Sensing Method = One-chip color area sensor
File Source = DSC
Custom Rendered = Normal process
Exposure Mode = Auto exposure
White Balance = Auto white balance
Scene Capture Type = Normal

[Thumbnail Info]
Compression = JPEG Compressed (Thumbnail)
X Resolution = 72
Y Resolution = 72
Resolution Unit = inch
JPEG Interchange Format = Offset: 772
JPEG Interchange Format Length = Length: 8261

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What mode were you shooting in? And what were the parameters on your flash.

Try putting the camera on M mode, dial in f/5.6, 1/200, ISO 200 - and have a look.

Welcome to POTN!

Since the original Digital Rebel (300D) doesn't have flash exposure compensation (FEC), you'll need to adjust it on the flash unit. In ETTL mode, hit the [SEL] button, then [+] or [-].

Flash exposure compensation is completely different from (ambient) exposure compensation. Boosting the EC won't affect the flash exposure.

When you're bouncing the flash, you'll usually want to use ISO 400, and setting the FEC to +2/3 or +1 is "normal".

(Hopefully a mod can move this thread to the flash section.)

Hi illy;
I was shooting in Auto mode, then switched to P, and put iso at 400, and exposure on +1.3. I tried the M mode as you suggested. I did get the histogram more in the center. I still got some weird results. My flash is on ETTL and I try and keep it on 60 degrees up. Even with flash straight ahead I get under exposure. I uploaded two images taken in M mode at the settings you sugested. I took about 50, my wife thinks I'm nuts. LOL. I was getting about 50% underexpsoures with the M mode. I did notice that it seems worse if the object is a chair or a person, vs a wall or picture. I have my camera on just the very center AF point mode. I put newly recharged batteries in too.
I got some pics that were real dark, and some just about perfect (for the first time). I thought these uploads were the best for comparison, the same sofa, same everything.

Hey! Thanks for trying to help me. I really appreciate it. I'm in the boonies, no local camera shop, just a Ritz in a dept. store.

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Sorry I post in the wrong place. Please forgive me. I thought I was under Canon Digital Cameras. Happy Holidays King Curtis. Thanks for the suggestions.

Hmm, is there a possibility that you dialled in some under exposure on your flash? Try using the flash exposure compensation button (where ever it is on the flash) and over expose it by a stop.

Well I took the suggetions of Curtis and Illy. I upped the exposure on the flash by a stop (1+) and that helped alot. I even switched back to P and Auto modes and got good results. I also put the diffuser window down, and that helped too.
Illy: I am pretty sure I didn't change the flash stop at all before. I really avoided changing any flash settings. I'd just turn it on, tilt it up, and take shots. I still got a few underdeveloped shots in the last batch, with the flash on 1+ stop. But it was only 2 out of 20, instead of 16 out of twenty. Still very strange!!!
Really appreciate the help. My wife now has lots of spots before her eyes! LOL Did you like her new dress?
Happy Holidays!

I just discovered something new. The hacked software for the Rebel offers FEC. You hold the "jump" button down, and turn the dial, to se the Flash Exposure Compensation. It is easier than pushing sel on the flash (very small buttons), and then pushing + several times.

glmccready wrote in post #2408490
my wife thinks I'm nuts.

She's probably right.

This is the EOS Digital Camera section. We also have a section for Small Flash and Studio Lighting. No biggie. We forgive Newbies. We even forgive Oldbies.

glmccready wrote in post #2408600
My wife now has lots of spots before her eyes! Did you like her new dress?

It's beautiful, and so is she. I demand you post more pictures of her!

Sometimes aiming the flash straight up works better than 60 degrees. It will produce more flattering light on your subject if you light up the ceiling above yourself, rather than above her. Another thing that can help quite a bit is an index card rubber-banded to the back of the flash to bounce a little light forward.

When you get a chance, print out the EOS Flash Bible (link in my Signature). It's a lot to read, but worth the time. Also the Flash Photography 101 articles might help. They're a lot shorter.