Canon 6D and Flash exposure

Canon cameras usually default to 1/60th shutter speed in P(automatic mode) when using Flash. The Aperture value depends on your lens, but usually its the largest Aperture on your lens. To avoid using the default mode of 1/60/ largest Aperture, I use to set the camera to M(manual) , set the Flash to ETTL, then set the shutter speed to 1/60 - 1/125 . From there I could use any Aperture value I wanted mostly f4 - f11. Since I was using ETTL with my 580 EX 2 flash, I could read the distance scale on the flash to determine the flash to subject distance.

 

This served me well for a while, but suppose I wanted to use the pop-up-flash, or a flash that did not have the distance scale on it. Would it be like playing crap shoot ? Even though the default is 1/60 shutter speed in 'P' mode, the camera allows you to change the Aperture value by turning the Control Wheel. Let's say the default Aperture value for my lens was F4 for Flash. I can still turn the Control wheel and change the Aperture value to f5.6 , f8 and f11, the shutter speed would remain the same at 1/60 though.

 

The Aperture Scale would show me that I was 1 stop, 2 stops or 3 stops under exposed, but when I looked at the pictures I took with those Aperture values, they all look properly exposed ? The only difference is the DOF (depth of field) and the ambient light mixture.

 

Right now I really can't test this under real life scenarios, but would I get the same results in real life and how do you explain this ?

Edited May 10, 2020 by hjoseph7

The apertures you used were within the available performance of your flash unit, so that it simply increased the flash duration as you used a smaller aperture in order to provide the same flash exposure on the subject. If you pushed the envelope by shooting at a more distant subject or bouncing the flash off the ceiling in a large room, you would find the aperture whereby the flash was using its maximum power would be insufficient, and then you would see the difference in the images

 

If you used a camera with a pop-up flash, you would not have a distance scale, and would have to go with trial and error. Of course the pop up flash units don't have much power, so it will run out of gas quickly if you try to shoot at small apertures. My general rule is to shoot with the camera on M when flash is the primary source of light and A or S mode for fill flash. I never shoot direct flash indoors, so the distance scale on my Speedlight is useless.

“Canon 6D and Flash exposure.” . . suppose I wanted to use the pop-up-flash, or a flash that did not have the distance scale on it. Would it be like playing crap shoot? Even though the default is 1/60 shutter speed in 'P' mode, the camera allows you to change the Aperture value by turning the Control Wheel. Let's say the default Aperture value for my lens was F4 for Flash. I can still turn the Control wheel and change the Aperture value to f5.6 , f8 and f11, the shutter speed would remain the same at 1/60 though . . . but when I looked at the pictures I took with those Aperture values, they all look properly exposed ? The only difference is the DOF (depth of field) and the ambient light mixture . . . how do you explain this?

 

The details of your test are vague.

 

Firstly we’d need to know exactly what Flash you used to make these sample photos. An EOS 6D doesn’t have a Pop-up-Flash, so it has to be some other Flash unit.

 

Secondly we’d need to know what ISO you used, or if you had Auto ISO selected.

 

Thirdly, we’d need to know the approximate Ambient Light conditions.

 

***

 

That stated - on the face of it, and in addition to what Ken wrote and which I agree - "the apertures you used were within the available performance of your flash unit", it seems the Flash that you used for these test photos had ETTL connectivity and that the Camera and Flash worked correctly.

 

Additionally, I’d guess that the Ambient Light was above EV 11~12 and the Flash was acting as Fill Light, which is also correct functionality when the Camera is in P Mode.

 

WW

If you used a camera with a pop-up flash, you would not have a distance scale, and would have to go with trial and error.

 

As a side note, and as you mentioned, the Pop-up Flash doesn't have much power, but, one can make a reasonable guess as to the Maximum Flash Distance at any given ISO by using the (inflated) Guide Number provided by Canon. I think that the GN hasn't changed throughout the EOS Digital Series and it's typically quoted as 43ft/ISO100.

 

So, using the PuF as the Key Light, and if (only as one example) you're using ISO400 @ F/5.6, you can reckon about 15ft is the Maximum Flash Distance, though, I'd estimate 12ft would be a safer bet.

 

Back around 2006, I did some tests attempting to reckon how useful the Canon PuF would be to use as Direct Flash Fill (in an emergency, at a pinch).

 

In a nutshell, my tests showed that the Guide Numbers are a little inflated, or at the least, don't represent a useful amount of "Fill Power" in the real world of Photography.

 

In open shade or similar, (assuming the Max Flash Sync is 1/250th or 1/200th), if you can pull around 1/200th @ F/5.6 @ ISO 200 to suit the Ambient Light, then you get around 7ft~8ft Camera to Subject as the Maximum usable Flash Fill Distance, even though the GN suggests more like 11ft; In back-lit/top-lit/side-lit sun, its essentially useless, sometimes OK to capture a Catch-light, though.

 

WW

The details of your test are vague.

 

Firstly we’d need to know exactly what Flash you used to make these sample photos. An EOS 6D doesn’t have a Pop-up-Flash, so it has to be some other Flash unit.

 

Secondly we’d need to know what ISO you used, or if you had Auto ISO selected.

 

Thirdly, we’d need to know the approximate Ambient Light conditions.

 

***

 

That stated - on the face of it, and in addition to what Ken wrote and which I agree - "the apertures you used were within the available performance of your flash unit", it seems the Flash that you used for these test photos had ETTL connectivity and that the Camera and Flash worked correctly.

 

Additionally, I’d guess that the Ambient Light was above EV 11~12 and the Flash was acting as Fill Light, which is also correct functionality when the Camera is in P Mode.

 

WW

I was using a Canon Speedlite 270EX . This flash comes with ETTL. The ISO was set to 100. Not sure about the ambient light, but in the room I'm in, I have to set the ISO to at least 800 to hand hold the camera. When I took the pictures not much light was coming in, if I remember correctly . I would say under those conditions I would probably need to set the ISO to 1600 to hand hold the camera without flash.

Thanks for the details.

 

Then we'll assume that the room light was less than EV11. In this case an ETTL Flash would work as the Key Light when the 6D is in P Mode C. Therefore (as Ken mentioned) the Flash had enough power to accommodate a reasonable exposure for all the Apertures that you selected. This is the explanation.

 

WW

I think I read somewhere that changing the Aperture (ambient exposure) on your camera does not affect flash exposure. This is only with Canon cameras and ETTL Canon flash. With Nikon cameras you can affect flash exposure by changing the Aperture on the camera. The thing I'm trying to wrap my head around is that if the camera automatically defaults to 1/60 @ F4 when in 'P' mode, then why is it telling me that I'm -1, -2 or -3 under exposed ?

I think that you are jumping between a few topics.

 

If you want to understand how the Canon EOS Camera works in P Mode with Flash, then I think it best that we just stick to that topic and don't introduce how Nikon Cameras work or generalize using out of context statements about how Aperture may or may not affect Flash Exposure.

 

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The thing I'm trying to wrap my head around is that if the camera automatically defaults to 1/60 @ F4 when in 'P' mode, then why is it telling me that I'm -1, -2 or -3 under exposed ?

 

The short answer: It's telling you that you have engaged Exposure Compensation.

 

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These are some of the functions of P Mode, when the camera detects an ETTL Flash -

 

1. The Camera does NOT ALWAYS default to 1/60th @ F/4. (Evidenced by Image #4 below)

 

How the camera chooses the exposure parameters when it detects an ETTL Flash, is controlled by the P Mode Algorithm and primarily, in this situation, the factors taken into consideration are:

> The Ambient Light Level reckoned by the camera's TTL Meter and the influence of the Metering Mode chosen

> The ISO selected

> The Maximum Aperture of the Lens

 

2. When you change the Aperture as you have described, then you are effecting Exposure Compensation.

 

Changing the Aperture will affect the Ambient Exposure and not the Flash Exposure PROVIDED the Flash has enough power to accommodate the Aperture you have chosen:

> for the Distance to the Subject

> at the ISO you have chosen

 

(For example only, if the camera originally selected F/4 and you then choose F/22 and the Subject was 40ft away in darkness and you're at ISO100, then, the choice of F/22 will very likely have an effect on the Flash Exposure – simply the Flash will have too much Falloff to adequately expose the Subject.)

 

3. Additionally, you can choose to use Flash Exposure Compensation either in addition to or exclusive from the Exposure Compensation.

 

4. Selecting Auto ISO adds other layers to what the Camera will choose to do, depending upon the exact shooting scenario, mainly it considers the Ambient Light Level, but the camera's decision making is not necessarily limited to that one aspect.

 

***

 

Below are six images of the same scene, which provided examples of only Points 1 and 2 above.

 

I have chosen not to introduce either Flash Exposure Compensation or Auto ISO into this conversation.

 

In these examples, the Flash was the Pop up Flash on a Canon DSLR and lens was an EF 50 F/1.4 Lens. The Metering Mode was "Evaluative" and the Ambient Light was constant throughout the test shots.

 

One common use of Exposure Compensation when using Flash Fill on an indoor scene is to better balance the exposure of the daylight scene outside, with the Flash-fill exposure of the indoor scene: this is evidenced in Image #5.

 

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Image 1

 

 

Image 2

 

 

Image 3

 

 

Image 4

 

 

Image 5

 

 

Image 6

 

(Yes - the first image is O/F and there is a spelling mistake – that’s all part of the fun)

 

WW