(1dx) Best way to use flash in Av mode?

Started Aug 18, 2013 | Discussions thread
qianp2k Forum Pro • Posts: 10,350
Re: (1dx) Best way to use flash in Av mode?

keithop wrote:

Hi

Apologies if this is a simple (atupid) question but it's confusing me at the moment.

1DX on Av mode. Aperture set to 1.4, fine, 580exII in ettl mode.

Be aware of Av mode indoor or low light as you need to watch shutter speed if flash works in fill-flash mode when there is strong ambient light indoor for example.  Better to shoot in M mode indoor to set specific aperture and shutter.  ETTL flash will automatically complement to ambient light to get correct exposure.

Just experimenting indoors to get familiar with the flash system and with the flash direct, all I get are hopelessly over exposed images.

Two possibilities here.

a) Your 580EX II is in TTL not eTTL mode at the moment that you can see on LCD, a common issue involves with 580EX II that happened to me many times.  Use more powerful batteries, clean hotshoe connector but FEC (flash exposure compensation) always will fix ETTL->TTL issue at the moment (that used to drive me crazy when it happened). That will cause over-flashing.

b) There are strong indoor light.  At F1.4 you shutter is beyond 1DX's X-Sync speed (1/250?) However by default, HSS is not turned on 580EX II (that is stupid as should be other way around that turn on by default, press button to turn off).  You need to press the button to turn it on that will stay until you take battery out.  So your 1DX will be set at 1/250 sec that also will cause overexposure.

I'd simply have expected the camera to work the shutter speed, iso and flash output to get the exposure reasonably ok but it seems to put the iso at 400, shutter speed not particularly fast (sometimes 1/25) and over expose :/

The reason camera set ISO to 400 automatically is because you use Auto ISO.  If you shutter is only 1/25 and aperture is f/1.4, it sounds 580EX II is on TTL mode.

I've reset all camera settings to make sure I'm not doing something silly so I must be missing something ?

If it's TTL issue as I suggested to use more powerful battery (such as 2500 mAh or above), clean hotshoe interface, and use FEC (change to a different value and then change back) that always will fix the issue then.

Thanks for any ideas

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