Flash compensation vs exposure compensation when using on-camera speedlite

Hi and thanks for the vibrant community. I'm hoping someone might be able to help me with the following?

I've been assigned holiday photo-taking duties, and I'm trying to figure out how the camera tries modifying the image when I use 1) flash comp and 2) exposure comp in TTL? Can I use flash comp to vary subject exposure while I use exposure comp to vary ambient exposure? Or, does exposure comp effectively vary the overall scene's (subject and ambient) exposure?

Another question along the same theme that might shed some light on the matter...although at the moment, it just has me even more confused. How am I supposed to read the live-view histogram when using flash? I notice that when using flash, the histogram is grey and generally pushed towards the left. Does this mean the live view flash histogram is purposely underexposing with the expectation that the flash will provide an additional light source?

Some additional details:
Canon EOS R
Shooting in aperture priority
Shooting in TTL (I know and have shot in full manual before, but kids are fast and I won't have time to dial in many settings before the moment is lost)
Using flash as either a fill light (daytime) OR as a primary light source for subject (nighttime) with ambient exposure coming from environmental lighting

Simone

Heya,

You can set EC on your camera to whatever you want and it will effect the camera's exposure.
TTL flash has it's own, FEC, which is indepedent of the camera's exposure. So you can tell it to compensate exposure separately.

So if you want ambient exposed down, you set a negative EC in your camera's exposure (say using AV mode, set aperture, ISO whatever). Then say you wanted to expose a subject with flash with a dakrer ambient, you can tell your TTL flash to expose at FEC zero, or if you wanted it as fill flash, -2/3rd or so FEC, or if you wanted to expose up, you could tell it to expose FEC +2/3rd or +1 or more. Your call.

Very best,

I'm not sure what is all means, but ambient and flash exposure with Av mode doesn't sounds promising.
The only time I recall to use exposure compensation at "-" side and with on camera flash was for low key portraits.


Then I use on camera flash for low light, I want shutter speed to be as low as possible to let sensor gather enough of the light. To help camera even more with this I increase ISO even up to 6400. All I do is watching light meter scale. As soon as I have indicator going closer to the middle, I set flash to something like -2/3 and it is good to go.
If I want more ambient light, I bounce the flash. If fill in, straight.

I also recommend to check the manual to find if here is no similar to this situation auto mode. Perhaps, with R Canon figured it out.
I recently purchased Oly E-PL1 and its fill in flash auto mode just works .

1. Exposure compensation effects how long the camera leaves the shutter open for the preset f/stop in Av
2. Exposure compensation affects the selection of the lens aperture for the preset shutter speed in Tv
3. Separate from 1 or 2,, flash exposure compensation affects how much light is output from The flash.

Thanks everyone for the detailed replies! One thing about photography is that it's not always easy to find others in real life (as in face to face) who share a similar passion to explore the hobby with. It's a difficult gap to fill, but thanks to the forums I do feel there still is a community...and, as in my example, it helps solve what at times seems to be life's greatest mysteries. =P

I've played around more with settings and reviewed results. I think the one variable that still applies is TTL...it's hard to guess exactly what the camera is dynamically computing to be an ideal result....but adjusting for that, it does make much more sense now.

It's nice outside! Hope to see you guys out shooting!

Yes, Canon does a superb job about NOT EXPLAINING a lot of things, including how things work!

1. In the case of eTTL, my understanding is that Canon (in the standard flash Evaluative mode) looks at all the flash zones which are focused at the same distance as the main focus location and mysteriously computes flash output from those zones.
   
2. And in the case of the other eTTL flash setting (of flash Average mode) it puts out enough light from the flash to light up the entire scene, background and all, IOW the entire frame area is considered, not merely selective focus zones.
   
   
3. Another theory is that with Evaluative flash metering, the Canon camera takes the ambient light into account when calculating the flash exposure. With Average flash metering, the flash metering would appear to be de-coupled from the ambient metering, and the camera is less biased by the available light.
   
   
4. Folks have adopted the practice that if you are shooting in Av mode in sufficiently bright light that results in a reasonable shutter speed is chosen for the selected f/stop, ie where flash is a Fill source, use flash Evaluative.
   
5. But in low light situations in which light is insufficient for a reasonable handholdable exposure, ie the shots in which the flash is the Primary source of light for the shot, choose Flash Average in the menu.
   
   
6. And then there are the mysterious and not discussed (by Canon) automatically done but hidden-from-users tweaks to ambient exposure and flash output which happen at specific low light levels to confound even pros about how the camera+flash will behave in a particular situation...NEVEC and AFR! ...subjects for those at the learning level of Flash 210 and 212, not at the level of Flash 1 and Flash 2.
   

Kinda late here but be careful shooting in Aperture Priority. If in a darker venue your system will do just that, preserve the aperture you select by lowering the ISO. Sometimes down to 1/15 or less. I have seem people get into trouble because they didn't know what was going on. The key is to shoot with a fast lens and bump the ISO up. A better option is camera on manual and flash on ETTL. (TTL option is for film).

Just to add what Wilt said. The flash itself has two modes, Evaluative and Average and these can only be changed via the camera flash menus. Also the flash and camera have two specific jobs. The camera exposes for ambient light and the flash exposes your subject/s. To make it easier for myself looked at it this way. The camera doesn't care what the flash is doing and the flash doesn't care what the camera is doing. Learning how to control both those exposures is what it is all about.

Evaluative metering. When you press the shutter half way down the camera takes the typical ambient metering using the multiple metering zones. At this point the flash is not involved as the cameras metering system cannot predict what the flash will do. When you press the shutter all the way the flash fires as pre-flash and the light from the pre-flash is reflected back to the camera. It isolates the closest object/s which is typically your subject/s and exposes for that. A bride in a white dress, and groom in a black tux and the couple together will all reflect light back differently.

ETTL flash has its own exposure system that works like the cameras ambient meter - but they don't work together. Just a step back for a moment. No flash. If you shoot pure white snow or pure black tar your cameras ambient meter will expose for 18% grey and the exposures will be off. For snow you have to overexpose and for tar underexpose. Half and half snow and tar in the frame will yield a good exposure without compensation. The flash exposure system does the same thing. That is what the EFC adjustment on the flash is for - ETTL. If you shoot with the flash on manual you adjust the power manually.

The reason Canon did this was to make AF independent of flash which allows you to focus and recompose without messing the flash exposure up.

Average metering. The closest object is not isolated. The whole scene is metered. Some like to use this indoors but it is not very good outdoors. I found it a pain to switch so I always shot in Evaluative unless I set the flash to manual for portraits.

As for shooting with the camera in manual I always did so indoors and mostly shot in Av outdoors. Here is an example of the control you have between the ambient and the flash exposure. Aperture controls flash exposure and shutter speed controls ambient exposure. The author just changed shutter speeds to change the effect.

https://neilvn.com …ues/dragging-the-shutter/

If you want to master your flash this is the guy. Read the tutorial in the blue column on the right.

https://neilvn.com/tan​gents/

Why adjust EC (or overall exposure including ISO) vs. FEC? I'm not asking, but thought that perhaps this thread could use a brief explanation of hwy one would adjust one vs. the other. The end results will differ.

- If you set the camera to a manual exposure, f/8, 1/125, ISO 400 (lets say the meter tells you this will be 3 full stops under exposed) and use ETTL with an onboard flash,. the ETTL will adjust the flash out put to make the subject under your focus point exposed correctly.

If the back ground is far away, it will not get the benefit of the flash as set by ETTL, and will be dark, often pure black depending on circumstances. You may want this.

If you do not, increasing the ambient exposure, lower shutter speed, larger aperture, or boosting ISO, will slowly bring the background lighting up in increments. You'd need to go close to the original 3 full stops to get it equal to the subject. ETTL will continues to drop it's power output as the ambient exposure increases.


- Fill flash Vs. main light source:
Back to 3 stops underexposed, in this case your flash is the main light source.
If you boost exposure and back off the flash eventually you are going to be using ambient light as your "main light" and the flash becomes just fill,. say for example you boost ISO until your subject is just 2/3 under exposed (ambient) and you back off your FEC down to - 2/3 or so. Now your subject is being lit mainly by ambient light, and the flash is just providing fill flash, reducing shadows, get some color in the yes etc.

Flash as main light, background disappears. (sorry for the harsh highlights, I did not have a modifier when I took these)

IMAGE LINK: https://jakehegnauer.z​enfolio.com/p506722924​/e3da2b45

digital paradise wrote in post #18972530
Evaluative metering. When you press the shutter half way down the camera takes the typical ambient metering using the multiple metering zones. At this point the flash is not involved as the cameras metering system cannot predict what the flash will do. When you press the shutter all the way the flash fires as pre-flash and the light from the pre-flash is reflected back to the camera. It isolates the closest object/s which is typically your subject/s and exposes for that. A bride in a white dress, and groom in a black tux and the couple together will all reflect light back differently...

Average metering. The closest object is not isolated. The whole scene is metered. Some like to use this indoors but it is not very good outdoors. I found it a pain to switch so I always shot in Evaluative unless I set the flash to manual for portraits.

As for shooting with the camera in manual I always did so indoors and mostly shot in Av outdoors. Here is an example of the control you have between the ambient and the flash exposure. Aperture controls flash exposure and shutter speed controls ambient exposure. The author just changed shutter speeds to change the effect./

I almost never have shot with camera's flash menu set to Evaluative, so I have little experience in that mode. As a result, I just conducted an experiment, both to educate myself about flash exposure behavior, and to illustrate (or not) what digital paradise just mentioned about closest object vs. (what I had apparently wrongly claimed earlier about 'all flash zones at the same distance as the subject' being considered in flash output). Here is the test:

Camera at ISO 400, set to M with 1/30 f/5.6 selected (causing underexposure by about -3EV); flash menu set to Evaluative
On the left shot (#1) I am standing about 5' from the camera, with focus zone on me; on the right shot (#2) I am standing about 12' from the camera, with the lens focused on me for each shot.

1. I am correctly exposed in shot 1, yet significantly underexposed in shot 2.
   
2. It is obvious that the focus distance has nothing to do with nothing, not even for the purpose of comparing zones 'at the same distance as the subject' except perhaps for highly reflective (metal, mirror) zones.
   
3. And the ceramic tea pot (to subject left in both shots) is very similarly exposed in both shots...reflecting digital paradise statement about exposure for 'what is closest to the camera'
   

1. If anything, this reflects the wisdom that flash Evaluative is best when using 'flash as fill', while flash Average is better when using flash as Main source, as it is for both test shots.
   
2. Both points 1 and 3 seem to negate claims that Evaluative exposes for the closest object....as I was 2-3' closer than the ceramic teapot in shot1, the flash should have seen me in higher intensity light (by about +1EV brighter so it should have output -1EV less light, considering the Inverse Square falloff of light!) so the ceramic teapot should have been a bit darker in shot 1.
   
3. Whan flash is Evaluative and the Main source of light, it does not seem to behave that much differently that I would have suspected Average to meter...the overall walls are about the same tone in both shots?! More testing is in order!