Question on Flash Photography


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SkyPipe

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#1
I have a few questions on flash photograaphy that always puzzle me.

Q1. Say you metered an object and is -1/3 then you use your flash in auto mode. Does this mean that the flash will automatically compensate to the right exposure ?

Q2. Say you still metered at -1/3 then still using automatice mode but with flash compensation set to +2/3. What is the exposure this time ? Is it (-1/3) + (+1/3) + (+2/3) ? or is it (-1/3) + (2/3) ?
 

Octarine

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#2
For Canon: Flash in automatic mode (ETTL) will focus on getting the right exposure for the foreground. This is directed by your FEC setting. Setting FEC to lower or higher values will result in different flash output.
Depending on your Exposure Mode the camera will either set shutter speed / aperture to have the background also properly exposed (Tv, Av) or or only the foreground (P). Here the Exposure compensation can be used to additionally influence the exposure for the background.
Please check the manual of your camera or google further for the specifics of your camera system. Details for Canon can be found here.
 

RedSuns85

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#3
Hihi, I also got a similar flash question...

I am using Nikon system and test using some Tumax flash, I set to TTL mode in the flash and fire to an object using aperture 1.8 and aperture 4..
The object could not get the same flash exposure with the 2 aperture, I thought that the subject shld get the same exposure since it is in TTL ? Also, the object is terribly over-exposure with F 1.8. Am I right to say third-party flash wun have as accurate reading as a Nikon Flash system ?
 

zac08

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#4
Hihi, I also got a similar flash question...

I am using Nikon system and test using some Tumax flash, I set to TTL mode in the flash and fire to an object using aperture 1.8 and aperture 4..
The object could not get the same flash exposure with the 2 aperture, I thought that the subject shld get the same exposure since it is in TTL ? Also, the object is terribly over-exposure with F 1.8. Am I right to say third-party flash wun have as accurate reading as a Nikon Flash system ?
Yes, its the compatibility that makes a lot of ppl say why a Nikon flash is always a better choice.

From the camera to the flash, they have to communicate with each other to check on terms of exposure values, and how the flash can effectively work to fill in the scene or illuminate dominantly.

Even when using Nikon flashes with Nikon systems, you'd need an understanding on how the flash works and how to compensate and work in different light scenes and conditions.
 

ZerocoolAstra

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#5
I have a few questions on flash photograaphy that always puzzle me.

Q1. Say you metered an object and is -1/3 then you use your flash in auto mode. Does this mean that the flash will automatically compensate to the right exposure ?

Q2. Say you still metered at -1/3 then still using automatice mode but with flash compensation set to +2/3. What is the exposure this time ? Is it (-1/3) + (+1/3) + (+2/3) ? or is it (-1/3) + (2/3) ?
From my understanding (i might try experiment on this and let you know later... you can also try it!!):

If you take a portrait and set EV to -1/3, the flash should light up your metered object enough for you to have -1/3 EV exposure.
If you set camera EV to -1/3 and flash EV to +1/3, the subject should now be 0 EV.

It also depends on your metering mode though. For more repeatability, you should use spot metering on exactly the same position.
 

Dream Merchant

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#6
What system are you using in the first place?

Different brands have different systems, and Canon's flash system, especially, works in entirely different ways.
 

ZerocoolAstra

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#8
I don't have such a combo, so I shouldn't say "yes it's like this, or no it's like that"...
My advice is to experiment when you have the free time, and understand how your camera + flash metering behaves in different scenarios. Then you can set it up accordingly when such a situation arises.
 

catchlights

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#9
Hi,

I'm using aCanon system with Sigma DS 500EF flash.
I'm not the best person to answer your question as I'm not familiar with Canon flash system.

Hihi, I also got a similar flash question...

I am using Nikon system and test using some Tumax flash, I set to TTL mode in the flash and fire to an object using aperture 1.8 and aperture 4..
The object could not get the same flash exposure with the 2 aperture, I thought that the subject shld get the same exposure since it is in TTL ? Also, the object is terribly over-exposure with F 1.8. Am I right to say third-party flash wun have as accurate reading as a Nikon Flash system ?
your info is not sufficient.

when flash on TTL mode, the camera meter will read the flash output thur the lens and tell the flash to stop output when the amount of flash is sufficient. But it does not mean you will have 100% correct exposure every time, if...
the flash to subject distance are too close, result: flash overexposure
the flash to subject distance are too far, result: flash underexposure
subject and background are overall in very light tone, result: overall underexposure
subject and background are overall in very dark tone, result: overall overexposure
subject occupied very small area, and background very dark, result: subject overexposure

and also,

if the ambient is already very bright and you flash does not support FP, or you didn't enable FP mode, it will overexposure too.

so you can't conclude the 3rd party flash is inaccurate, unless you know what are you doing and do a test together with a Nikon flash for side by side comparison.
 

Dream Merchant

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#10
Hi,

I'm using a Canon system with Sigma DS 500EF flash.
I was about to pass you the encyclopedia to the EOS Flash system, but with Sigma ... it might not be all relevant and may end up confusing you more.

Sigma has a DS flash?

I thought their series was either DG ST or DG SUPER? http://www.sigmaphoto.com/flashes/flashes_flashes.asp

Anyways, you can easily find out the answer to your question by setting up a test.

Do ONE controlled exposure with everything set to 'ZERO' aka 'correct exposure. It is CRUCIAL that you shoot a well-balanced test subject that shows a wide range of exposure values. It's not much use if you shoot say something with a lot of whites, or blacks.

Using that controlled exposure as a reference, go ahead and do what you asked in your original questions and compare the test results.

Be sure to process ALL the photos using the same exact parameters and settings.

All the best.
 

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SkyPipe

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#11
Sorry, should be DG Super.

Also, with ETTL, in computation, does it takes into account the flash is bounce to the ceiling ?

I'm always puzzle how much must I compensate, that is increase the flash exposure, when bouncing... Think a lot depends on what type of ceiling and how high....

Think Trial and Error is the best way to learn.
 

RedSuns85

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#12
I'm not the best person to answer your question as I'm not familiar with Canon flash system.

your info is not sufficient.

when flash on TTL mode, the camera meter will read the flash output thur the lens and tell the flash to stop output when the amount of flash is sufficient. But it does not mean you will have 100% correct exposure every time, if...
the flash to subject distance are too close, result: flash overexposure
the flash to subject distance are too far, result: flash underexposure
subject and background are overall in very light tone, result: overall underexposure
subject and background are overall in very dark tone, result: overall overexposure
subject occupied very small area, and background very dark, result: subject overexposure

and also,

if the ambient is already very bright and you flash does not support FP, or you didn't enable FP mode, it will overexposure too.

so you can't conclude the 3rd party flash is inaccurate, unless you know what are you doing and do a test together with a Nikon flash for side by side comparison.
Thanks catchlights & ZAC,

After doing some testing, I conclude that the tumax flash i-TTL is not accurate. I tried taking on a subject 1-4 meter away using a large aperture of 1.8, it is always over-exposed in a normal indoor environment. If I stop-down to aperture like F4, it seems normal again
 

madmartian

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May 2, 2009
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#13
I'm using the Tumax flash on a nikon system & I got no problems with the i-TTL at all. ;)
 

catchlights

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#14
Thanks catchlights & ZAC,

After doing some testing, I conclude that the tumax flash i-TTL is not accurate. I tried taking on a subject 1-4 meter away using a large aperture of 1.8, it is always over-exposed in a normal indoor environment. If I stop-down to aperture like F4, it seems normal again
it does not seem to be the i-TTL is not accurate, each flash has it working range, you are out of the flash working range, not because of too far but it is too close.

try shoot something beyond 4 meters or lower your ISO when you shooting @f1.8
 

zac08

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#15
Thanks catchlights & ZAC,

After doing some testing, I conclude that the tumax flash i-TTL is not accurate. I tried taking on a subject 1-4 meter away using a large aperture of 1.8, it is always over-exposed in a normal indoor environment. If I stop-down to aperture like F4, it seems normal again
As Catchlight has explained... it's not all down to the system. When you're shooting too close, even Nikon flashes will over-expose. This is when you need to know the power and adjust accordingly. I tend to shoot at -1.0 flash EV when pointing the flash directly at the subject or even when bouncing off the ceiling when I'm about 1-2m away from the subject. :)
 

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