Hi..new to this forum. I have a probably dumb question on Canon Flash

[tshore]

Hi...by way of introduction I've been shooting semi-seriously for about 10 years, over which time I have acquired a fair amount of Canon gear. Mostly I shoot sports and wildlife, and have little experience with flash photography. To the extent that I get baffled sometimes by fairly basic questions.

For example, I read the article discussion FEC for Canon (in particular) in the CiC site: https://www.cambridgeincolour.com/tu...ra-flash-2.htm.

I got confused regarding the discussion of setting FEC and EC to achieve a certain Flash Ratio. I understand from the article and other sources that for Canon FEC impacts only the flash portion of the exposure, while EC impacts only the ambient portion. So far so good.

What I found puzzling was this:

"As an example of why EC is much more complicated than FEC, let's walk through what happens when you change the flash ratio from 1:1 to 2:1 in the above example. You will first want to dial in +1 FEC, since that's the easiest part. However, if only FEC is increased +1, then the amount of light from flash doubles while light from ambient remains the same — thereby increasing the overall exposure. We therefore need to dial in a negative EC to compensate for this, so that the exposure is unchanged. But how much EC? Since the original flash ratio was 1:1, the total amount of light using +1 FEC is now 150% of what it was before. We therefore need to use an EC value which reduces the total amount of light by a factor of 2/3 (150% * 2/3 = 100%). Since each negative EC halves the amount of light, we know this EC value has to be between 0 and -1, but the exact value isn't something we can readily calculate in our head. It's equal to log2(2/3), which comes out to about -0.58."

I get that in this case, if you had a 1:1 flash ratio (meaning flash and ambient contributed equally), and were to increase FEC +1, you would double the flash output, and the ratio would become 2:1, as the ambient would remain unchanged.

I also get that the resulting combined exposure would now be 150% of what it was before.

What I don't understand is how a reduction in EC of 1/2 to 2/3 can get the total exposure back to what it was, if it only impacts ambient exposure. Having doubled the flash output, that increased output by itself is now equal to the entirety of the original exposure. It seems you would then have to reduce the ambient contribution to ZERO to achieve the same total exposure. Which, in addition to being impossible, would also inflate the flash ratio to infinity.

It seems to me the answer to the question of how to increase the flash ratio in this example from 1:1 to 2:1 while keeping total exposure the same would be something like this: Say (arbitrarily) that the exposure coming from flash was 100 and ambient 100, for a 1:1 ratio. Total exposure = 200. We want to solve for y = flash exposure and x = ambient exposure such that x+y = 200 (total exposure the same) and 2x = y (flash ratio 2:1). A little algebra gets you x = 66.66, y = 133.33. Translated into stops, that's about +.4 stops of FEC, and -.6 stops of EC.

What am I missing? The blurb above seemed to be describing the way Canon's EC works, but maybe I misinterpreted, and it's describing the Nikon convention, where EC impacts overall rather than just ambient exposure.

Thanks

Tim

[Manfred M]

Tim - my understanding is that the article is correct for older Canon models, but some of the more recent models use the same approach as Nikon where EC and FEC are not internally coupled and must be set independently. I understand with most Canon models, the description in the CiC article is correct, but as I shoot Nikon, I can't confirm this aspect of Canon operation from personal experience.

The moment we start looking at lighting ratios, it implies we are using off-camera flash, likely with some form of light modifier. This means that the lights are set up to photograph a subject who is in a predetermined location and does not move out of where he or she has been positioned. I always set my flash to manual in these shooting situations and set up my lighting / lighting ratios using my hand-held incident light flash meter. I get far more accurate and consistent light that way. While I have used FEC / EC when using a hot-shoe mounted flash in a "run & gun" shooting situation, I've never used it with multiple light sources and suspect I never will. These are situations where I shoot in 100% manual mode.

If you want to try these techniques I suggest the best way to understand them is to set up and try them.

[dje]

It seems to me the answer to the question of how to increase the flash ratio in this example from 1:1 to 2:1 while keeping total exposure the same would be something like this: Say (arbitrarily) that the exposure coming from flash was 100 and ambient 100, for a 1:1 ratio. Total exposure = 200. We want to solve for y = flash exposure and x = ambient exposure such that x+y = 200 (total exposure the same) and 2x = y (flash ratio 2:1). A little algebra gets you x = 66.66, y = 133.33. Translated into stops, that's about +.4 stops of FEC, and -.6 stops of EC.

What am I missing? The blurb above seemed to be describing the way Canon's EC works, but maybe I misinterpreted, and it's describing the Nikon convention, where EC impacts overall rather than just ambient exposure.

Thanks

Tim

Tim I'm no flash expert and I have to say that, until now,I have never read all of the tutorial you referenced. However I can't disagree with your maths. A telling extract from that part of the tutorial you quote is "We therefore need to use an EC value which reduces the total amount of light by a factor of 2/3 (150% * 2/3 = 100%)". This suggests to me that the example is based on the case where EC effects ambient and flash exposure.

Perhaps Manfred as a mod could refer this to Sean (site owner and tutorial author) for clarification?

As a general observation, it seems to me that trying to set a precise value of flash ratio with FEC and EC is hardly worth the bother. For casual shooting, I use manual camera settings (with flash turned off) to adjust for the amount of ambient exposure i want and then turn the flash on with TTL control to fully expose the image. I then use FEC for fine tuning of overall exposure. For my sort of shooting the balance between ambient and flash is not that critical.

Dave

[tshore]

Thanks for the responses. Looking at the excerpt again, I think it likely is describing the Nikon usage of EC when using flash. I agree that targeting a precise flash ratio is probably not worth the bother. In practice, I am more interested in managing the contrast within a subject (e.g. shadows on faces) and the relative exposure of the subject relative to the background. By my question here, I was just trying to make sure I had a grasp of the fundamentals...next stop, trial and error.

[Manfred M]

Tim - this side of flash photography is hard to explain in words and one can only really come to grips with it in using this functionality. Getting out there and trying them helps make sense of them.

I used EC and FEC during a shoot last week, when I was doing some work for a local charity. I was asked to photograph volunteers delivering donated furniture to refugees. Unfortunately, the lighting was terrible photographically (bright, sunny late summer day) with the volunteers offloading a delivery truck.

The images were hard and the light was changing, depending on where I stood to shoot and the volunteers happened to be. The rapid movement meant that shooting on manual was not going to work. The background light was very bright and fooled my camera's light meter into underexposure, so I dialed in EC to fix that issue. Adding regular fill flash gave the images too much of a hot and flat look, so I reduced the flash output via FEC to compensate for that issue.

I used both the camera's histogram and view I got on the display to judge the appropriate amounts of compensation I wanted. This type of issue is typical of "gun & run" type shooting.

Volunteers & Furniture

[pschlute]

Like Manfred and Dave, I use Manual camera and flash exposure when using multiple light sources. A flash compatible light meter is essential.

The other confusing factor is the way EC is implemented. If it is done via aperture or ISO it will have a direct impact on the amount of flash light recorded as hitting the subject. If done by Tv adjustment it will in most cases have zero effect !

[Manfred M]

If done by Tv adjustment it will in most cases have zero effect !

If you are just using flash, I would agree, but if you are blending ambient light and light from flash, that is not necessarily correct. As I said earlier in this thread, EC + FEC are tools I generally only use when shooting ambient light + fill flash.

[William W]

IF the OP is using Canon DSLRs, and IF we are discussing using Speedlights, especially Hotshoe or on a Quick Release Bracket of even in a bundle of two on stands, then, for the way I work and the way my brain works, I've found it practically simpler to never use EC when using FEC.

There are several reasons, the main reason is having 'user focused premeditated' control over the Shutter Speed and Aperture - hence I would be in Manual Camera Mode, always. For me this premeditated control is especially important when shooting under the pressure of time and/or through varying lighting scenarios.

WW

[rpcrowe]

I don't know if I interpreted the question correctly but here is the way I use fill flash outdoors for shooting a model/subject. The dinosaur that I am, what is now called fill flash used to be know as "syncro-sun"

Shooting with manual exposure, I get the exposure the way I like it for the background (the ambient light), which is sometimes a slight bit darker than if I were aiming at correct exposure for the background alone. This is especially true if my subject is backlit by the sun...

That is it! I no longer adjust the exposure with the camera. Exposure for the model/subject which with the ambient light is usually quite a bit under exposed but, I do not adjust this on the camera. Instead, using manual exposure with my flash unit or on the remote trigger if I am using off camera flash, I make a trial exposure.

I get used to the approximate manual exposure depending on which flash I am using, the distance of the flash to the subject and the general ambient light - so that trial exposure is usually fairly close. Say, my test manual flash exposure is 1/4 and the model is still too dark - I increase the flash exposure manually; conversely if the model is over exposed, I decrease the exposure. Usually I have it correct by the second shot although I sometimes need a third for optimum exposure manually.

I've been doing this type of adjustment with Canon DSLR cameras and with my Sony mirrorless cameras. I will say that the Sony cameras have an advantage since I can view the results of the flash adjustment through the eye level viewfinder. That is a lot easier to see and adjust in bright sun than trying to view the image on the camera LCD and a lot faster since I don't have to chimp...

You could usually pretty be in the ballpark with most camera/flash combinations by using TTL and adjusting the exposure on the subject by using + or - FEC.

I will sometimes use a combination method with the Flashpoint/Godox TTL 360 by getting the initial flash exposure with TTL and converting it into manual flash exposure for adjustment. That is the best of two worlds that is available with this unit. I will still not adjust the exposure via the camera but via the Flashpoint/Godox remote trigger. There is usually only a slight need for exposure change when using the TTL 360.

Remaining with manual flash exposure ensures that the exposure on the model/subject remains somewhat constant... If my flash to subject distance changes, I will often just increase or decrease the flash exposure by 1/3 to a full stop. A quick view of the results through the EVF will let me know if I have adjusted the flash exposure correctly This keeps me at an exposure that I can work with in PP. An added advantage to this is that the process can be used with a flash that is not integrated with the camera through TTL...

When shooting dogs that are not running around, I will most often use Aperture priority with the TTL flash dialed down since my main reason for using the flash is to achieve a catch light in the eyes. When shooting running dogs or dogs moving fast for any other reason, I usually don't use flash at all since I will be shooting in burst mode (manual with auto ISO) and I have no flash that will recharge fast enough to keep up with even the slowest of my camera's burst speeds.

One final mention... There are times when using on camera flash when even at maximum output, the flash is not powerful enough to fill in my subject. The only cure to that problem is either to open the aperture and adjust the shutter speed accordingly or to get closer to the subject which will impact the exposure for the background. This will happen frequently if the only flash I have with me is the TT350S which is small and pretty under powered for anything but close up shooting... A compromise can be to carry a more powerful flash and/or use off camera flash with which the flash to subject distance is not determined by the camera to subject distance...

[apersson850]

Yes, when mixing flash and ambient light, you have to consider if they both illuminate the same surfaces, or if the flash illuminates one side of the subject and the ambient light the other.
Depending on what you want to accomplish, the action to take in the two cases is usually not the same.