some ?? on flash photography

[davidreeves]

I recently purchased a Sigma EF500 ST DG for my Canon Digital Rebel XT and I also bought a StoFen diffuser.

Most of my shooting is HS and College basketball games. I somehow got roped into taking individual and team pictures of a little girls basketball team, portrait shots. I am really new with flash photography and would appreciate someone sharing their wisdom with me.

I grasp the bounce flash concept and have taken a few practice shots in the place I will be shooting.

It seems like most of the time when I use the Sigma flash, I wind up with serious overexposures. The attatched pic is an example. It was taken in a meeting room, (the one I plan to use to take the team pictures) no outside lighting, fluroscent lighting, Sigma 28-70 f2.8 lena at 70mm, the sigma flash (ef500 dg st) with diffuser and the flash pointed straight up at the ceiling which is white ceiling tile and the ceiling height is about 10 feet. I was about 20 feet from the subject in this picture. Adjusting the flash head downward slightly increases the overexposure problem.

Use of the diffuser also seems to increase the over exposure issue and I thought it would do the opposite by providing more even lighting. I do have the flash compensation setting on the camera set to underexpose slightly and the flash itself is set for TTL

All that said can someone give me some rule of thumb guidelines? It there a way to tone down the flash strength?

Would appreciate any comments.

Thanks.

[davidreeves]

Thanks in advance for your help

[Canuck935]

Hmm I'm not familiar with this flash. If your flash can be set to an auto or manual mode I would try that.

[Ronnoco]

I have that flash and it does not overexpose. Have you checked where there is flash exposure in your camera menu to see whether for some reason it is in the + overexposure area?

Ronnoco

[JSPhoto]

Use manual settings on the flash and dial it down a step at a time. BTW, what are your settings? (ISO & shutter).

JS

[drg]

This looks like you may also be needing to compensate exposure for a 'dark' subject. Dark subject always have a tendency to overexpose and light subjects like snow, underexpose.

Try adjusting the flash to manual so that for the aperture you are using that the distance scale on the flash is about the same as how far you are shooting and try some photos. Then, adjust the camera to slightly underexpose (either with +/- EV setting) or by using a smaller physical aperture, higher f-number. Do not change the shutter away from the proper sync speed. Shutter speed has little affect on flash as long as it is synchronized. The flash duration is so short that only the Aperture will make a difference.

I'll dig up a manual for the ST or get one online if you have any other questions.

[davidreeves]

Thanks for your comments.

The Sigma flash is a TTL flash ands supports E-TTL. It was set on the TTL settings.

The flash compensation setting is set to underexpose slightly.

Here is the EXIF info:

Make - Canon
Model - Canon EOS DIGITAL REBEL XT
Orientation - Top left
XResolution - 72
YResolution - 72
ResolutionUnit - Inch
DateTime - 2006:10:25 17:48:46
YCbCrPositioning - Co-Sited
ExifOffset - 196
ExposureTime - 1/30 seconds
FNumber - 3.20
ExposureProgram - Aperture priority
ISOSpeedRatings - 400
ExifVersion - 0221
DateTimeOriginal - 2006:10:25 17:48:46
DateTimeDigitized - 2006:10:25 17:48:46
ComponentsConfiguration - YCbCr
ShutterSpeedValue - 1/30 seconds
ApertureValue - F 3.20
ExposureBiasValue - 0.00
MeteringMode - Multi-segment
Flash - Flash fired, compulsory flash mode, red-eye reduction mode
FocalLength - 34 mm
UserComment -
FlashPixVersion - 0100
ColorSpace - sRGB
ExifImageWidth - 1024
ExifImageHeight - 766
InteroperabilityOffset - 9230
FocalPlaneXResolution - 3954.23
FocalPlaneYResolution - 3958.76
FocalPlaneResolutionUnit - Inch
CustomRendered - Normal process
ExposureMode - Auto
WhiteBalance - Auto
SceneCaptureType - Standard

Maker Note (Vendor): -
Macro mode - Normal
Self timer - Off
Quality - Fine
Flash mode - On + red-eye reduction
Sequence mode - Continous
Focus mode - One-Shot
Image size - Large
Easy shooting mode - Manual
Digital zoom - None
Contrast - High , +1
Saturation - High , +1
Sharpness - High , +2
ISO Value - 32767 (other)
Metering mode - Evaluative
Focus type - Auto
AF point selected -
Exposure mode - Av-priority
Focal length - 28 - 70 mm (1 mm)
Flash activity -
Flash details - External TTL
Focus mode 2 - Single
White Balance - Auto
Sequence number - 0
Flash bias - 2047.00 EV
Subject Distance - 0
Image Type - Canon EOS DIGITAL REBEL XT
Firmware Version - Firmware 1.0.3
Owner Name - unknown
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Camera Serial Number - 1120621676
File number - 355 - 5551

[another view]

This looks like you may also be needing to compensate exposure for a 'dark' subject. Dark subject always have a tendency to overexpose and light subjects like snow, underexpose.

Since you were shooting TTL, I'll bet this is a big part of it. 80% or so of the above image is a fairly dark background. It's not black but it looks like (in real life) that it would be slightly darker than a grey card. The metering system is trying to average out to neutral grey and led to overexposure.

The guy's face is a very small part of the overall image and the camera has no idea that this is the part that you want to be exposed correctly, so you'll have to "tell" the camera this somehow. This could be with a compensation on the flash or using a manual setting.

Is this the background that you plan on using? If not, keep in mind that a light background could (and probably would) have the opposite effect. It would be nice to have more distance between the subject and background too, but that's not always possible.

[livin4lax09]

when you bounce, your flash can no longer read what focal length you are at, and no longer reads how far away your subject is, so it doesn't put off the exactly correct amount of light a good amount of the time. Just shooting in Manual like JS said will help a lot.