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dhphoto
November 7th, 2006, 11:57 AM
This is carried over from a large thread at FM, in the hope someone who 'really knows' can answer.

Is it correct that using exposure compensation on a Canon dslr *does not* affect the flash output?

i.e. if you dial in + or - exposure compensation (not FEC) the flash will still output precisely the same amount and will be unaffected?

TIA

David

Chuck Westfall(Canon USA)
November 7th, 2006, 02:06 PM
Yes, that is correct.

Best Regards,

Chuck Westfall
Director/Media & Customer Relationship
Camera Marketing Group/Canon U.S.A., Inc.

John Sheehy
November 7th, 2006, 07:26 PM
This is carried over from a large thread at FM, in the hope someone who 'really knows' can answer.

Is it correct that using exposure compensation on a Canon dslr *does not* affect the flash output?

i.e. if you dial in + or - exposure compensation (not FEC) the flash will still output precisely the same amount and will be unaffected?


It will try to be unaffected. It is not supposed to make a difference, but if you are in Tv-pri mode, and a negative EC forces a higher f-stop, then the flash might be unable to deliver its exposure.

dhphoto
November 8th, 2006, 01:32 AM
Thanks all, I had no idea this was true, even after using Canons for over 25 years professionally!

David

Nill Toulme
November 8th, 2006, 08:15 AM
I didn't either, and I'm glad to know it. At first I was astonished to hear it, but then on reflection I realized that it makes perfect sense and is as it should be.

Nill
~~
www.toulme.net

Dave New
November 8th, 2006, 01:27 PM
I understand that this is counter to what Nikon bodies do, so folks that have shot previously with Nikon, may be surprised at the different behavior exhibited by Canon.

There really is no 'wrong' or 'right' here, but it helps to be aware of these kinds of differences, so you can better control the outcome when shooting with flash.

John Sheehy
November 8th, 2006, 03:17 PM
I understand that this is counter to what Nikon bodies do, so folks that have shot previously with Nikon, may be surprised at the different behavior exhibited by Canon.

There really is no 'wrong' or 'right' here, but it helps to be aware of these kinds of differences, so you can better control the outcome when shooting with flash.

The Canon way is inconvenient, IMO; poorly thought out. I think that the ambient EC should also affect the flash, and that the FEC should work relative to the *achieved* exposure. I'd rather have an under-exposure that is 75% ambient and 25% flash than a full exposure that is 10% ambient, and 90% flash, as happens when you shoot in light too low for the highest ISO in Tv-pri or manual mode.

John_Nevill
November 8th, 2006, 04:42 PM
Amazing, I never new this!

I've been using a combination of EC and FEC for years, convinced that I knew what I was doing....At least I can now own up to it!

Why did I sell my OM4?

Sean DeMerchant
November 8th, 2006, 06:25 PM
The Canon way is inconvenient, IMO; poorly thought out. I think that the ambient EC should also affect the flash, and that the FEC should work relative to the *achieved* exposure. I'd rather have an under-exposure that is 75% ambient and 25% flash than a full exposure that is 10% ambient, and 90% flash, as happens when you shoot in light too low for the highest ISO in Tv-pri or manual mode.

I disagree. What you advocate here is loss of control. For instance, when dragging the shutter one can dial in -2/3 EC and -1/3 FEC for a reasonable exposure regardless of the light. If they were linked, then you could not do this.

Albeit, I typically drag the shutter in full manual and tweak FEC to suit.

one opinion,

Sean

Asher Kelman
November 8th, 2006, 06:41 PM
Sean, I have a rather basic nomenclature question. Why don't we express exposure as a simple factor like

E 0.33 and FE 0.67, total =1.0

0r else 33% ambient, 67% total 100%

This would allow easier imagination of how light is distributed. Anyway, how do you cary this math in different circumstances. In external flash we allocate power by Watt seconds or percent. Why not with the camera?

Asher

Sean DeMerchant
November 8th, 2006, 07:22 PM
Hi Asher,

Sean, I have a rather basic nomenclature question. Why don't we express exposure as a simple factor like

E 0.33 and FE 0.67, total =1.0

0r else 33% ambient, 67% total 100%

The practical answer is that we can dial in FEC and EC on camera. So talking about the camera settings is more practical even if it is less obvious/intuitive.


This would allow easier imagination of how light is distributed.
I agree with this pedagologically, but again at the end of the day we have to deal with decades of ingrained practice/tradition from the camera manufacturers.

Why has no one released an expose to the right metering pattern? It would be helpful for serious shooters who do post work. Practically, it means if the average consumer grabs a camera in the metering mode they will get lots of overexposed (soft light) and underexposed (hard light) images that cannot be printed directly due to a need for post processing (though it would be cool to see this integrated with RAW and JPEG to do this implicitly behind the scenes). But again, it would change standardized behavior.


Anyway, how do you cary this math in different circumstances. In external flash we allocate power by Watt seconds or percent. Why not with the camera?

This will not work in practice because Watt-Seconds are not a valid unit for measuring light. The problem here is that this unit of optical prowess must be run through lighting modifiers of some sort (even bare bulb usage shapes the light) and the distance of the subject from the light source affects both the reflected and incident light on the subject. Whereas incident and reflected measures of EV are consistent regardless of the light source. So by measuring the EV we integrate* away a layer of complexity. Hence, one simply dials in a flash EV measure and does not deal with factoring in the the light distribution of a light source (this term integrates away light modifier size, efficiency, the light distribution at the source), the light sources intensity/power/..., and the light sources distance from the subject which would then need to be combined (integrated) to get a prediction. Or we can simply ignore it and measure the EV from the camera viewpoint (reflected metering) or from the subject location (incident metering). And the EV is what we use for calculating exposure (which is greatly simplified using stops/EV/base 2 logarithm).

some thoughts,

Sean <smile>



* To integrate something is to add it together and create a summary measure of what is dealt with that obscures underlying detail and illustrates aggregate behavior. Or in mathematical terms to integrate over something is simply to add it up.

John Sheehy
November 9th, 2006, 04:15 AM
I disagree. What you advocate here is loss of control. For instance, when dragging the shutter one can dial in -2/3 EC and -1/3 FEC for a reasonable exposure regardless of the light. If they were linked, then you could not do this.

Albeit, I typically drag the shutter in full manual and tweak FEC to suit.


Dragging the shutter is not practical in many types of photography. I cconsider that a special effect, and sure, you should be able to do that, but there should also be the option to do it my way, too, because there are many situations where all you really care about is the ratio of light.

Canon is too lacking on options.

Norman Hom
December 1st, 2006, 11:14 AM
Is it correct that using exposure compensation on a Canon dslr *does not* affect the flash output? i.e. if you dial in + or - exposure compensation (not FEC) the flash will still output precisely the same amount and will be unaffected?

Yes, that is correct.

wow, this is a gem! i shoot both nikon and canon and have been pulling out my hair over not being to change my D200's flash behavior via EC and/or FEC and make it behave more like my canons...i thought i was going nuts but now i know the reason.

Will_Perlis
December 1st, 2006, 02:54 PM
"0r else 33% ambient, 67% total 100%"

I've run into that with Sekonic light meters. You hit the button and they give you the percentages. Then, after all those years of thinking in stops, I have to sit down with a computer and figure out what that's telling me. (or look at the little, tiny, minuscule scale which shows the ambient and flash in stops.)