I have a Bonica flash setup that I use with about everything. It has a Bonica flash on a single arm and an Ikelite flash on a duplex arm. Both are light sync'd from the camera flash. I have a Bonica SeaKing2, an MM2 and a Canon AS6, they all work just fine with it.
With the Canon digitals however I keep getting over exposures. I am sure that there has to be some exposure setting that I am missing and will give myself a Homer "DUH" slap when someone points it out.
I visited the Canon Digital underwater site. EXCELLENT Site: http://www.canon.co.jp/Imaging/uwphoto/index-e.html
They show a flash and macro lenses, but when I contacted them it was a whole different story, what a run around, do they actually read the questions? I hate canned responses..

Original Message Follows:
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I have an A10 and an A40 that I use with an underwater case. When I use an external flash the pictures are real dark and I can not seem to find
any settings that will overcome this. The only thing on the "Underwater" site is that external flashes are available..
Thanks

CANON RESPONSE
Dear Clint,
Thank you for writing to us.
Unfortunately, Canon USA does not offer an external flash for the waterproof case of the PowerShot A10 or A40. We apologize for the
inconvenience this will cause.
Sincerely,
James
Product Support Representative

Original Message Follows:

I have an external flash for it. I just can not find the correct setting to stop overexposure.

CANON RESPONSE
Dear Clint,
Thank you for contacting Canon product support.
We are sorry to inform you that Canon does not supply specifications to other manufacturers nor do we test with other manufacturers' products.
Therefore, there is always the possibility that they will not interact properly with our cameras. Accordingly, in order to realize the maximum
performance of this unit and thereby achieve the highest possible image quality, we recommend that you use Canon brand name accessories. They are designed and manufactured to match the special qualities of your Canon product.
Thank you for choosing Canon.

Sincerely,
David
Product Support Representative
Customer Satisfaction... The most important product we support!

"Customer Satisfaction... The most important product we support!"

LOL!
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BTW first you state:

"however I keep getting over exposures."

Then you state in the actual letter to Canon:

"pictures are real dark"

and finally, you state:

"I just can not find the correct setting to stop overexposure"

I assume the second quote is accurate, yes?
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BTW I do not own a Canon Digicam and therefore are not familiar with it's settings. Please understand that these are just general guidelines and opinions:

The Canon A series is most likely a preflash type digicam. In order to determine the correct amount of flash necessary for a good exposure, it sends out a series of mini flashes that the camera uses to compute and capture the actual exposure.

You state that your strobes are light sync'd. I assume that means once the external strobe senses a light burst from the flash unit on the digicam, a signal is received that will also ignite the substrobe simultaneously. If the substrobe ignites on the preflash but is unable to recharge itself completely before the main light outburst of the intrinsic strobe, the result may be an underexposure.

Does this potentially explain the situation? If so, one solution is to get a substrobe that ignores the preflash. S&S YS 90 DX has this feature as do the Ikelite DS 50 and 125 controlled with a manual controller. Inon (D 180 or 220 ) and Epoque (ES 150 DS) may also, but I'm not positive.

Another possibility may be that that Canon flash is not being forced to fire every time. Depending on settings, the digicam may feel that a strobe is not necessary. Usually this happens in Auto Mode where a slow shutter speed and large f/stop is chosen by the camera. Do you have a menu setting to force the flash regardless?

If you are actually getting overexposures, then one option is to choose a smaller f/stop in manual mode, if the camera has this feature. Remember that artifical strobe lighting can be controlled by aperture and distance. If you do not have the option of controlling aperture, get longer strobe arms or manually choose a lower ISO setting.

hth,
kbob

I knew it, I have a "DUH" slap coming. I post this and I get an message from another source. Yes, I was using AEmode. I was informed I should be using full manual mode with decreased shutter speed, increased fstop, 400 iso and to practice in the back yard to get a good idea of what settings to use. He also mentioned to always use spot metering if on auto. "DUH"

Clint,

Are you getting over or under exposed images?

The shutter speed will only influence ambient lighting and motion control, not strobe lighting. That is unless you choose a speed that is so quick that it clips some of the substrobe's light output.

ISO 400 seems a bit much. There would be a potential for noise at that level. The difference between ISO 100 and 400 is a couple of stops. I would suggest trying ISO 200 if you're still overexposing and it's an option available to you. The difference between ISO 100 and 200 is equal to HALF as much light!

Underexposure, overexposure, maybe I should read my posts before I hit "SEND"! The dark one OK? "DOUBLE DUH" It's been a long week.....no brain left.

That is what was fustrating me, I could see overexposure due to the added flash. Except I was getting VERY DARK pictures. I guess that on AE mode the iso is automatically set at 50-150. But what may be the biggest thing is that I didn't set the metering to spot and the camera was picking up the flash, lowering the ISO and shutter speed. I was trying to correct this through the exposure compensation function with no results. I'm going to take some picture of dead flowers tonight in manual mode and see if I can "brighten" things up. Thanks for the responses.

Just one clarification.

With ISO's, the higher the number, the higher the sensitivity the film, CCD, or CMOS has to light. The lower the ISO setting, the more light is needed for proper exposure. In order to create an equal image, ISO 50 needs twice as much light to enter the lens and be seen by the CCD, etc. as ISO 100 does. If you're experiencing underexposed images, one option is to raise the ISO. Conversely, if you are overexposing, lower the ISO. Again, this is only one option available to controlling exposure. It would most likely not be my first choice. I'd set the ISO to 50 or 100 and adjust the strobe to subject distance accordingly after choosing a desirable aperture.

This is all moot of course if the problem is with the preflash and your strobes are not able to recycle fast enough to keep up with the multiple discharges.

Spot metering usually means that the camera is concerning itself with the center most section of the viewfinder, between the brackets that appear similar to this:
[ ]
Otherwise, it is averaging the total image in the viewfinder for it's exposure calculations.

When I get a chance, I'll jump over to dpreview and see if I can find the specs on your digicam.