flash - exposure question

ceriltheblade wrote in post #11999390
wilt and tkbslc - thanks for the explanations.

So there **IS** a different protocol on flash use between settings.

I was missing that piece of information.

Now with those facts, I guess I need to figure out better how to use the flash. (thinking to himself outloud - I think i saw a video about the 430 and 580 exii - maybe I will check into it)

for those poeple who understand - WHY does the flash system act this way? thanks a lot!

Blue statement is not right.
1. The flash always behaves the same...ETTL exposure with flash tells it to expose the subject correctly (for discussion purposes, let's pretend FEC -- which is a human adjustment made to flash exposure -- isn't a consideration)
2. Independently, the ambient light exposure is made per the meter readings (again, EC is a human adjustment to automated exposure, and not a consideration for this discussion)
3. The Ratio of Fact1:Fact2 determines the relative contribution of flash.

• If the balance is Flash > Ambient, the flash predominates over ambient and is the main source of illumination, and the ambient-only part of the frame is darker than the ambient+flash part (the subject)
  
• If the balance is Flash < Ambient. the ambient is the main source of illumination, the flash fills in deep shadows reducing lighting contrast.
  
• If the balance is Flash = Ambient, the shot typically appears somewhat unnatural because the eye is not accustomed to seeing fill (which bounces off walls or even the ground) be as bright as the Main (the sun, whether filtered by clouds or not)

sorry for my thickheadedness -

so the the only difference then is the time of exposure for a give aperture value chosen by the camera as per its internal protocol vs the manually chosen time and aperture?

So because the photographer who takes into account both the ambient light as well as the fact that he using flash (or - at least s/he is supposed to! ) will purposely set a different t and AV value than the computer who will only use the av value to calculate the t value without respect to planned flash usage....

did I understand correctly?

I think you did.

The question if E-TTL II behaves differently depending upon the exposure mode has been asked several times in this thread.
The answer is actually that it's one of the exposure modes that behave differently when you are using flash - the P mode. By using a custom function, also the Av mode can be made to behave differently, but normally it does not.

P, Tv and Av all try to expose the ambient light properly. The difference with P when using the flash is that then, and only then, is it limited to a longest exposure time of 1/60 s.

Both Av and Tv will try to expose the ambient light properly. Since most people tend to use Av with flash (before they understand that M is better), you often run into the issue with the shutter speed getting very long, since the camera first tries to get the ambient light correct, then add some flash to that. Actually, the automatic modes change a little, if they see that it's within their domain to get the ambient exposure 100% correct. If it is, they lower the exposure about one stop, to avoid the added flash to cause overexposure.

If you for some reason try to use Tv with flash, you'll see the same thing. The camera exposes the ambient correctly, then add flash. However, since you are likely to "run out of apertures" sooner than you "run out of shutter speeds", the camera frequently can't expose the ambient correctly, if it's reasonably dark, and therefore selects the largest aperture the lens has and flashes for underexposure in the viewfinder. But enable Safety shift and you'll see you get about the same result as with Av.

Since Av very well can run all the way down to 30 s, there's a custom function to limit the range of the selectable shutter speeds, when using Av with flash. You can lock it to the fastest sync speed, but the point of that is limited, since you can just as well select M and set the aperture and shutter speed as you like. Newer cameras also allows Av to limit the selectable shutter speed to the range from 1/60 s to the sync speed. That's the same range as you get with P mode, just with a freely selectable aperture.

In M mode, of course, you select the aperture you perfer for the flash, then set an exposure time to match, in the way you want your picture to come out.

Many do use the M mode to reduce the intensity of the ambient, vs. what it would be if Av was left on its own. This is the reason why they say that Av makes the flash do fill, but M makes it the main light.
This is of course not true at all. It's the photographer who in Av mode can select if the flash is main or fill, through a custom function, and it's the photographer who selects main or fill in M mode, by rolling the dials.

E-TTL II is all the same.

ceriltheblade wrote in post #11999652
So because the photographer who takes into account both the ambient light as well as the fact that he using flash (or - at least s/he is supposed to! ) will purposely set a different t and AV value than the computer who will only use the av value to calculate the t value without respect to planned flash usage....

When the camera chooses a different shutter speed (for a given aperture in AV) due to the flash, you can see this in the display. For instance I just metered on the wall next to me in Av and got 1/30 and f/6.3. When I turned the flash on, the shutter went to 1/60. That's NEVEC, a fairly well-known feature.

If the Av settings that the photographer is starting with are based on having the flash connected, then those settings will be the ones actually used and they can be directly compared to the manual settings. I metered elsewhere and shot in Av at 1/4 second with E-TTL flash, and again in M at 1/4 second with E-TTL flash, and they appear to be exposed identically.

and is one more important setting at flash: evaluative and average. From camera.indoor is good to set at average and outdoor evaluative. But now i'm working only on average everywhere cause flash is more consistent.

again sorry for being a noob - but the flash itself has evaluative or average setting?

Manual is just that. You set everything in the camera to expose the capture and balance the lighting situation.

AV is a semi automatic mode and the camera will auto adjust everything but the Aperture to gain what it thinks is the proper exposure when using ETTL

Same with TV, only the camera uses everything but the set shutter to obtain proper exposure as it see's it using ETTL.


That's the main difference between the modes. Manual, semi auto and auto.
They will all use a different control setting based on what the camera decides, except for manual mode. You're the decision maker 100%

Also understand that how your metering system is set can have an effect too. Spot "VS" Center Weighted "VS" Evaluative.
Shutter speed controls ambient light and Av controls flash, as a rule of thumb.

ceriltheblade wrote in post #12010392
again sorry for being a noob - but the flash itself has evaluative or average setting?

Many people say ETTL works better indoors on "Average" and outdoors(as fill flash) on "Evaluative". It can also just be a personal preference and what you are most used to.

I use mainly use my flash indoors with "Average" and it seems to work well.

Here is an older thread that goes into great detail about it. https://photography-on-the.net …d.php?p=879962#​post879962

gosh darn it all - i hate it when , after reading all these manuals that come with the hardware, I still missed something! argh! thanks msowsun for the extra link and discussion. I am now more confused! and thanks canonistul for the heads up.

this lighting stuff sometimes is so $%^!@$^( difficult for those of us who shoot maybe 1-2 times per week as a hobby! Maybe when i retire, I will have time to really learn photography that I should have....

Well thanks to all of you in POTN who are helping me in small amounts each time!

in average mode flash is more consistent. same setting but on evaluative if must compensate the flash, power was very different. in evaluative ,compensate was +1 and in average was only +1/3. save batteries power.and again is more consistent.

canonistul wrote in post #12012767
in average mode flash is more consistent. same setting but on evaluative if must compensate the flash, power was very different. in evaluative ,compensate was +1 and in average was only +1/3. save batteries power.and again is more consistent.

How are you judging that EV information ? What format are you shooting in ? Raw or Jpeg ?

The amount of flash exposure using an OEM flash for Canon is identical, regardless of mode. Only the background exposure is modified.

The attached photo was taken using Av mode, TTL mode set to Average (not Evaluative). The overall exposure was 5 seconds. I made a minor flash adjustment to prevent blowing out the dress.

When I shot events, I always shot on Manual to guarantee the minimum shutter speed and guarantee my f/stop was always f/8.

There are many discussions surrounding Average vs. Evaluative TTL, and for those that use single-point focusing like me, Average produces far better exposures than Evaluative. Multi-point focusing reduces the severe underexposure of Evaluative, but it also creates many mis-focused pictures.

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Average TTL is more consistent flash exposure depending upon your focusing and framing method. Under Evaluative, the exposure is apparently judged based upon the activated focus points. Since I use single-point focus, this caused flash exposure to basically be determined like a spot meter in the center of the photo. For my style (close cropping, single point focus), Average TTL produced a very high percentage of good exposures. Using Evaluative, I got 2/3 severly underexposed photos (2-4 stops under).

canonistul wrote in post #12012767
in average mode flash is more consistent. same setting but on evaluative if must compensate the flash, power was very different. in evaluative ,compensate was +1 and in average was only +1/3. save batteries power.and again is more consistent.

The behavior of evaluative flash metering has changed quite a lot between E-TTL and E-TTL II. The emphasis towards the AF points, that was very strong in E-TTL, has been reduced in E-TTL II. Instead, a more complex use of the camera's zone metering system is utilized, in order to try to evaluate where the main subject is.

apersson850 wrote in post #12013161
The behavior of evaluative flash metering has changed quite a lot between E-TTL and E-TTL II. The emphasis towards the AF points, that was very strong in E-TTL, has been reduced in E-TTL II. Instead, a more complex use of the camera's zone metering system is utilized, in order to try to evaluate where the main subject is.

Isn't the face recognition programming the biggest difference in ETTL and ETTL-II