Canon flash and white balance

admirable

admirable

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Jim
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When I fit my canon flash to the camera and switch on, the flash should auto set the WB to flash.

How can I check that it's doing this?

If I look on the rear screen it shows auto.
 
You do not say models of camera and Speedlite, but...

Why do you think that the camera's WB should change when the flash is installed?

If the camera is in WB = Auto, then it will still display Auto, but use Flash for an exposure if there is a powered-up flash mounted. "Auto" does not display the actual values used.

Added: Take two shots, one in Auto and one in Flash, and compare the output to confirm. Buried in the EXIF data there are numbers which software can use for the "as shot" WB values, but they are not intended for human evaluation.
 
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1D IV and a 600EX-RT

test shots,

WB set to auto and temp reading is 5300-5350
WB set to flash and temp reading is 7200.

Camera fixed on tripod
 
Agree with SB, though I believe that Canons have the ability to adjust flash auto-WB according to power output* to counteract slight blueness at lower power/shorter durations (when gun is fired direct in straight ahead position).

I've never seen much evidence of it myself, but could that be happening? How are you measuring colour temp?

*Source Chuck Westfall.
 
HoppyUK said:
Agree with SB, though I believe that Canons have the ability to adjust flash auto-WB according to power output* to counteract slight blueness at lower power/shorter durations (when gun is fired direct in straight ahead position).

I've never seen much evidence of it myself, but could that be happening? How are you measuring colour temp?

*Source Chuck Westfall.
Click to expand...

Yes, introduced with the 580 I believe. There was a lot of noise about it at the time it was introduced.
 
HoppyUK said:
How are you measuring colour temp?
Click to expand...

Adobe camera raw.


I've Googled it and there's a fair bit about this issue on the net so I'll need to have a read.
 
The degrees Kelvin and the two tint adjustments are determined during the shutter-press sequence when in Auto mode.

The colour temperature of the Xenon tube is measured and reported back by the flash, after the shot but before the LCD jpeg is created.

(Only a few radio triggers return this data to the camera, e.g. YN-622C.)
 
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admirable said:
Adobe camera raw.


I've Googled it and there's a fair bit about this issue on the net so I'll need to have a read.
Click to expand...

So you're shooting a fixed test subject, colour correcting the Raw file manually, and then noting the difference on the ACR sliders? That's fine, but it wouldn't show any WB control shift, automatically applied or not, as that's not present on the Raw file. In other words, the only way you'd see a colour shift from Raws on an A vs B comparison is when the colour of the light is changing, for whatever reason.

Or are you loading up the images to ACR, and just noting the colour shift automatically applied to the JPEG thumbnail on import? In that case, ACR mimics the camera-applied settings.

In other words, how exactly are you assessing WB, as it makes a difference.
 
Camera fixed on tripod. WB set to flash. take shot. Repeat but change WB to auto.

open file from card in PS via camera raw 6.7 note slider settings

Flash WB = temp 7200 - tint + 26

Auto WB = temp 5350 - tint + 7

Straight from the card..........no adjustments made or sliders touched.
 
Why would putting the flash on force it to flash WB?

What if you gel your flash it'll be all wrong. I'd expect in auto it still does it's normal best guess like it does without the flash it's just aware you are using a flash.
 
Calzor Suzay said:
Why would putting the flash on force it to flash WB?

What if you gel your flash it'll be all wrong. I'd expect in auto it still does it's normal best guess like it does without the flash it's just aware you are using a flash.
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I was told years ago that when you fitted a canon flash on a canon body the WB was set to flash.

Obviously if you gel the flash the WB will be wrong.

You would think that auto setting would mean auto and the camera setup would recognise that the body had a flash fitted and the flash WB setting would be very near the auto setting but it's not.

I never had this issue with the 580EXII
 
admirable said:
Camera fixed on tripod. WB set to flash. take shot. Repeat but change WB to auto.

open file from card in PS via camera raw 6.7 note slider settings

Flash WB = temp 7200 - tint + 26

Auto WB = temp 5350 - tint + 7

Straight from the card..........no adjustments made or sliders touched.
Click to expand...

And presumably you can see a visible difference in colour? Flash firing directly forward.

Numbers aside, and they're always confusing I find when using non-Canon software, it looks like the camera is applying an AWB colour adjustment according to flash power output. Try changing flash exposure to confirm?
 
My understanding is that AWB is a guesstimate made by the body whilst Flash WB is either fixed or reported by the flash (status of PFn 5 on the flash)

Bob
 
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