Exposure Problem with 420EX

[JMSetzler]

Greetings to the group....

Test Photos: http://www.pbase.com/jmsetzler/420ex_flash

I received my 420ex flash unit yesterday so i wanted to do a set of test photos with it.

Shot 1: onboard flash / camera fully auto mode (not P mode)

Shot 2: 420ex flash head on / camera fully auto mode (not P mode)

Shot 3: 420ex flash head on with omnibounce installed / camera fully auto mode (not P mode)

Shot 4: 420ex flash bounced from ceiling / camera fully auto mode (not P mode)

Shot 5: 420ex flash with omnibounce bounced from ceiling / camera fully auto mode (not P mode)

The first shot in the series is the only one that is correctly exposed (using the onboard speedlight). Viewing the exif data on these photos, the camera decided to use ISO 400 for the shot with the onboard flash. The remaining shots with the 420ex flash, the camera decided to use ISO 100 which caused 2 stops of underexposure.

My question is: why, in fully automatic mode, did the camera with the 420ex choose ISO 100 with relatively identical shutter and aperture settings?

I am new to flash photography and I'm trying to understand more. My primary objective with the flash, at this point in time, is for simple point and shoot indoor photography.

[Dukeofurl]

None of your shots were underexposed per se. Your 420EX put out enough light to allow for almost (but not quite) two stops less exposure. You can (and should) goose up the contrast and brightness with Photoshop. The fact that a little post-production processing is needed is *not* considered a deficiency of either the camera or the flash. It's part of life.

The reason that the camera with the 420EX chose ISO 100 with relatively identical shutter and aperture settings is that it was Canon's decision that you are better off with the lowest ISO setting that your lens's largest aperture will allow so that you will get the lowest (or no) noise. As long as you are satisfied with your lens's sharpness and depth of field at that aperture, it was the correct decision. When your subject matter requires more depth of field, change to P mode and manually increase the ISO.

[justme_dc]

The 420EX has more power than the internal flash on the 10D that alone explains why the camera in auto mode switched from 400iso to 100iso. With more flash power at it's disposal it dropped the iso setting.

The E-TTL preflash from the 420EX probably read off those white sheers in the window, giving you an underexposed image. The same thing happens in the snow, if you metter off the snow you'll get grey underexposed pictures. white backgrounds require exposure compensation of at least +1 stop, usually +2.

Auto modes are not all things to all people, it takes it's best guess and gives what it thinks will be the correct exposure. Most of the time it works ok, you just happened to find one of the situations that will confuse the auto mode.

Try using the modes on the other side of the green square (P, Av, Tv, M) and apply a +1 or so to the flash. Likely your results will improve drastically. These modes can be used in a point and shoot fashion as well but you retain control of the cameras functions.

good luck.

[DonCoon]

No problem. Take one of the "under exposed" shots and #1 into editing SW with a levels tool and do an Auto Levels Adjustment. You'll have two fine pictures. (Personally, I always do manual levels adjustments.)

Having said that, I have noticed the problem frequently before with the 420 on my 10D. But since I've gotten into the habit of always checking the histogram, I just set FEC accordingly --- making sure not to blow out any highlights.