Author Topic: [Invalid] Flash WB/Tint  (Read 3134 times)

LordPanzer

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[Invalid] Flash WB/Tint
« on: September 11, 2013, 01:16:50 AM »
I read something about a flash photo technically being a double exposure since there's the flash light and the ambient light. This got me thinking, is it possible to use different WB/Tint settings for the flash exposure to simulate a gel?

Audionut

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Re: Flash WB/Tint
« Reply #1 on: September 11, 2013, 01:27:41 AM »
No, because the final exposure is a combination of the flash part of the exposure and the ambient part.

John Kesl

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Re: [Invalid] Flash WB/Tint
« Reply #2 on: September 11, 2013, 02:13:03 AM »
The short answer is yes, it just depends on the balance of your flash vs. the ambient. If you overpower ambient by at least 2 stops you will begin to see the flash WB more and more. Try setting your camera to tungsten and use your flash all things will be blue. Try dialing in green or mangenta and see the difference. Also, when you shoot moving subjects with flash @ shutter speeds below 1/15th, you'll really begin to see the double exposure effect. Though it is more of a freeze motion with other blurred stuff around it. I recomend shooting @ dusk and messing with your white ballance and exposure to see what you can do. The slower shutter speeds are more interesting. I say dusk, due to the variance of color temperature you'll encounter and then you can really experiment. Remember, everything is relative, Content to Composition to color temperature(the cameras setting and the WB "Setting" of the world around you to Exposure to contrast ratio.
(Ever done a bulb exposure using nothing but flash as the shutter?) those are cool too. (And you can still them in this digital age)
So, yes it is a double exposure of sorts, but only when the flash begins to act as the shutter (when it's dark outside). Because the shutter opens beginning the exposure but the flash acts as the shutter because it creates the light needed to actually illuminate the scene sufficiently enough to reflect photons back to the recording medium, causing exposure (in the old days of the halides) these days of the pixels. The shutter being open allows the photons in, but the flash is the mechanism which creates the duration of the exposure, much like a shutter would ordinarily do.
One last thing, get an off camera e-ttl flash extension cord ( cause who says the flash always has to illuminate from 8 inches above the axis) or (who says the flash has to illuminate what's in front of the camera at all) why not the tree behind your subject or maybe a side light. Flash is fun and powerful especially when you can move the two (camera and flash) independently.
 

Audionut

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Re: [Invalid] Flash WB/Tint
« Reply #3 on: September 11, 2013, 03:59:08 AM »
So, yes it is a double exposure of sorts, but only when the flash begins to act as the shutter (when it's dark outside). Because the shutter opens beginning the exposure but the flash acts as the shutter because it creates the light needed to actually illuminate the scene sufficiently enough to reflect photons back to the recording medium, causing exposure (in the old days of the halides) these days of the pixels. The shutter being open allows the photons in, but the flash is the mechanism which creates the duration of the exposure, much like a shutter would ordinarily do.

Shutter controls ambient exposure and ambient exposure alone.  A flash pulse is faster then the sync speed of the shutter, hence shutter speed does not affect flash exposure.
Flash photography involves 2 exposures always.  The ambient exposure and the flash exposure.  Just because the ambient exposure is clipped to black does not remove that exposure from the output.  This is of greater importance to understand where ambient exposure is a significant proportion of the total exposure.  Changing shutter speed will not affect the flash part of the exposure, it will control the ambient part of the exposure only.
Flash duration is limited by the flash hardware and the flash power.  Higher power flash increases flash duration.


You cannot simulate a gel with ML.  You can change the WB/tint settings sure, but you can only accomplish this for the entire exposure.  A gel only affects the WB/Tint for the flash exposure.

John Kesl

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Re: [Invalid] Flash WB/Tint
« Reply #4 on: September 11, 2013, 04:07:32 PM »
I forgot to add,
Since your on camera flash is a small localized source, when you change the white balance for your exposure from that flash (Say for example you make your WB 3200 and plus 8 magenta) it's only in post, when you correct back to daylight, that you will see the effects on the rest of the scene. To be more clear.
If you are shooting a subject horizontal wide angle, and that subject is a person. You are framing the individual half chest to top of head. they are standing in front of the ocean, it is about 6 pm. Your flash is set to overpower daylight by 2 1/2 stops. Your WB is 3200. You shoot the photo. In the computer you open your image, the image is too blue on your subject. when you correct the white balance to be pleasing on the skin tone (back to 5000) what you will discover is that your background is now much more orange than it was. This is a result of your main light being "incorrectly" White balanced for the exposure. And when you correct it voila. Your on camera flash is a small source. And it's light falloff is governed by the inverse square law, which states that for every doubling of distance your flash looses half it's power. ex. If you measure f/8.0 2 feet from your flash, it will be 4.0 @ 4 feet and 2.8 @ 8 feet. Therefore, rarely does your flash have the power to illumiate your subject and the background fully. And in that is your control over it's WB in relation to your surroundings.

Audionut

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Re: [Invalid] Flash WB/Tint
« Reply #5 on: September 11, 2013, 04:25:33 PM »
Therefore, rarely does your flash have the power to illumiate your subject and the background fully.

The fact that the flash does not illuminate the background fully is exactly the problem.  That's why you gel a flash in the first place, to match it's WB to that of the background.

And in that is your control over it's WB in relation to your surroundings.

How?  When you adjust the WB settings in post to fix the flash temperature, you also adjust the WB settings for the ambient.  The only relationship there, is that either your subject lit under flash, or the ambient exposure has the incorrect WB setting.  Because you haven't gelled the flash WB to match that of the ambients WB.

The only way to simulate a gell in post is via selective WB control via masks/adjustment brushes or whatever.  This is well outside the scope of the functionality of ML.

a1ex

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Re: [Invalid] Flash WB/Tint
« Reply #6 on: September 11, 2013, 05:01:55 PM »
selective WB control via masks

It might be possible to figure out a mask of what is covered by flash and what isn't (or what was the contribution of the flash on each picture). Of course, it requires two pictures, and if they are not perfectly aligned, it's going to create halos.

So, you can research it, but there's nothing that ML can help you with (you need to take two pictures and do the math, that's all).

Audionut

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Re: [Invalid] Flash WB/Tint
« Reply #7 on: September 11, 2013, 05:15:05 PM »
To be honest, that sounds like an awful lot of development work, for possibly a very limited set of circumstances where it works without significant flaws.

Vs

A cheap bit of colored plastic!