I hope this is the correct forum, not under Canon. Anyway:
I just upgraded my 5D's 430EX to the 580EX II.
I will be using it sometimes with another 1-2 lights (probably AB's) in which case it will just do fill, but when using only the single shoe-flash & a diffusor, the difference between this and the 430EX is incredible. REALLY significant. (I mention this for the benefit of anyone on the fence about upgrading.)
Anyway, here's what puzzles me:
With my 430 mounted, in Av mode & shooting in dim light, when I turn on the flash, the camera seems to know and I see the shutter speed increase substantially. However, this is not happening with the 580, even in ETTL mode. Sure enough, the camera is slightly over-exposing unless i manually dial it down a hair.
I have glanced through the manual, but can't find the answer. Surely the 580 is at least as intelligent as the 430. What am I doing wrong?
Not sure why the shutter speed would change when flash is simply turned on, but not all things Canon flash does is easily understood by observation. The shutter speed used for the actual exposure in Av mode is based on the zone-by-zone evaluation of both the ambient and pre-flash hitting the viewfinder (where metering is done) just after the shutter is pressed and before the mirror lifts and exposes the sensor.
When a master / slave arrangement is use there are several bursts of control and metering pre-flashes to determine ratio and exposure and communicate instructions to the slave(s). Be aware if trying to use multiple Canon flash with the ABs that the pre-flash will trigger the optical slaves in the ABs before the shutter opens. Even in M mode the Master will emit command pre-flashes to instruct the slaves. The only mode where there is no pre-flash is when a single flash is used with wireless off in M mode. The workaround is to fire the ABs via radio connected to the camera PC socket.
FWIW, Av mode isn't the best choice in dim light because dim light will cause shutter speeds to slow beyond what can be hand held. Better to use M and manually select shutter speed that is the best compromise between background ambience and shake prevention. Then exposure can be controlled with one variable, the amount of FEC used to override the camera metering best guess at exposure. Because the camera is reacting to reflected light how a flash shot is composed can greatly affect exposure. Keeping the subject closest to the flash and large in the frame gives the metering a better chance of guessing correctly. I've found it simplest to use evaluative ambient and flash metering. I let the camera make its logical guess based on relative brightness of zones, evaluate using the overexposure warning and histogram, then adjust FEC shot to shot as needed. Keeping the highlights 1/3 stop below clipping in the OEW results in well exposed highlight detail.
cgardner wrote:
Not sure why the shutter speed would change when flash is simply turned on
Chuck, I meant when the flash is on & after focussing. The 430 definitely results in a faster shutter setting, while the 580 does not. Weird. I still haven't figured it out.
Good to know about the pre-flash. Bummer. Of course, I could always live with that if I can't spend for a Pocket Wizard. (I've been spending waaaay too much on gear, and now that I've discovered Leica lenses I'm really in trouble!)
cgardner wrote:
FWIW, Av mode isn't the best choice in dim light because dim light will cause shutter speeds to slow beyond what can be hand held. Better to use M and manually select shutter speed that is the best compromise.....
Yes, I'm mostly in agreement at this point. I had hoped that the 580, by being brighter, would have resulted in an even faster shutter speed (in Av mode) but alas it isn't causing ANY change. The 430 will take me from 1/8 sec to about 1/50 in really bad conditions, at 1600 ISO.
-So what do you do? Shoot underexposed and brighten things in post?
Cableaddict wrote:
-So what do you do? Shoot underexposed and brighten things in post?
My conceptual model for using flash indoors is a stage. I want to shine the spotlight on the star, and use the fall-off of the flash to hide all the distractions in the background. Tonal contrast is used to separate background and foreground the same way selective DOF does.
That of course is the opposite of the Fong-o-matic paradigm of bouncing most of the light off the ceiling and lighting up the entire space like an overcast day. But the DIY diffusers I use have a top flap which can either bounce all the flash output forward, or be angled partially or fully open to bounce varying amount of fill off the ceiling like the $$$ Fong gizmo. So when I do want more background context in a shot I will open the flap, zoom the flash to max (105mm) and tilt it to aim it at a point on the ceiling in the middle of the scene :
This shows the set-up. The panel of the diffuser on the fill on my camera bracket still bounces some light forward into the foreground, but most of the fill goes up and off the ceiling 30 ft. above. Note the bright spot on the ceiling (a second off camera flash is on stage left also lighting the background).
Here I intentionally wanted to call attention to the guy in the checkered shirt in the audience because the church pastor and his wife in dark clothing are sitting next to him. I also wanted the pull the viewer over the people in the foreground, past the speaker, into the crowd in the background to create to impression of moving in the space. I had to walk completely around the room to place the off camera flash and set that one up
When there is sufficient time for set-up and I want to precisely control the rendering of the background I will use a separate group C flash to illuminate it:
To answer your second question I do post process most flash shots with masked screen and multiply adjustment layers to selectively lighten and darken layers. Most often I darken the edges and unimportant details I couldn't crop out to eliminate them as distractions.
I use two flashes in a neutral fill on bracket / key off camera configuration because it allows precise control of the lighting pattern, lighting ratio and exposure of the foreground subject. From 1974 to 2005 I used pairs of manual Vivitar 263 and 285HVs flashes, but find the Canon TTL wireless ratios much easier in candid situations. With the camera in M mode I set the shutter for the desired amount of background ambience and DOF for a balance of focus and resolution. Often the problem is too much ambient light of a different color temp affecting skin tone in the foreground so my starting baseline is usually 1/125th at f/5.6 to eliminate the effect of the ambient. f/5.6 is near the sharpest resolution of the lenses I use and since the flash falls off anyway there isn't much point in stopping down further which makes the flash work harder to created the same exposure. I like the entire face to be in focus so I rarely shoot wider than f/4 with flash. I take a test shot and adjust from the 1/125th @ f/5.6 baseline as necessary for each situation.
With Canon ETTL I just dial in the desired ratio and control exposure with one simple variable: FEC. ETTL reacts to refected light which changes shot to shot. Evaluative metering sorts out what is brightest and tries to guess how important it is by what zone it is in and the difference in reflected flash vs ambient. It rarely gets the exposure perfect, but once FEC is adjusted to the scene reflectance the exposure will be consistent shot to shot. I monitor exposure shot-to-shot by keeping the playback in the mode that shows clipping in the highlights in the over-exposure warning. I find that keeping the FEC 1/3 stop below the point where whites with detail start to clip results in correct exposure of highlights. I'd rather be a bit underexposed, which is easy to correct in post, than lose highlight detail during capture. I wish the camera had the option to show the clipping warning on the full size playback: it is the most valuable feedback there is on exposure showing when and where highlight detail is being lost.
With my diffusers the starting baseline for FEC is +1 stop and usually varies between +1 and +2 for most scenes. The advantage of using two flashes is controlling the dynamic range of the scene with the lighting ratio. The off camera light creates the highlights, the amount of fill used controls how much shadow detail is revealed. It makes holding the detail in a white wedding dress and revealing the detail in the grooms black suit quite easy
In AV mode Canon flash i used as a fill light and thus will not affect the overall exposure based on the ambient light. This is true for all Canon flashes 580, 430 or even the build in one.
The flash will change metered exposure only when it's used as a main light source which is P or M camera mode.
VladKenner wrote:
In AV mode Canon flash i used as a fill light and thus will not affect the overall exposure based on the ambient light. This is true for all Canon flashes 580, 430 or even the build in one.
Canon flash has constantly evolving, not particularly well documented technology. A big change occurred in 2004 around the time the 20D arrived on the scene with what is called ETTL II. The previous flash metering ETTL had a flash algorithm which used the active AF point(s) in the calculation and include automatic fill flash adjustment based in the EV level of the ambient light. The details are on NK Guy's site but if memory servers it kicked in between EV9 and EV13. There was a C.Fn to override the automatic fill function.
ETTL II uses evaluative metering by default. On the 20D the ambient and pre-flash is compared zone-to-zone over 35 zones. That allows to camera to determine the brightest areas, the darkest, the dynamic range of the scene and also by comparing ambient levels of with pre-flash it can create a radar like map of how far the things in each metering zone are. Zones with stuff closer to the camera will typically reflect the same amount of ambient light as objects further away, but more flash in inverse proportion to the distance from the flash. The metering also uses the focus distance from some USM lenses in the calculation. It is wickedly smart, up to a point. It assumes the brightest reflections are coming from detail that needs to be preserved and tends to err on the side of not blowing the highlights. Thus dialing in some at least +1/3 is the normal baseline for most average scenes.
There is no C.Fn for canceling auto fill flash on ETTL II bodies so I suspect the type of automatic fill flash adjustment based on EV level used in ETTL bodies may be incorporated into the overall evaluative metering algorithm. But I can't recall seeing any Canon documentation to that effect. So how flash metering works will vary from model to model of camera.
It is important to realize that EC and FEC are overrides of the camera's best guess not absolute power levels and the baseline (zero EC / FEC) "guess" will change very time the camera is moved. There are so many variables in play in a shooting situation its difficult to second guess how the camera will meter a scene. That's why I use the baseline approach of shooting a test frame at zero EC and FEC when in Av mode., evaluating it, then adjusting from the camera's best guess.
The best way to keep ETTL II evaluative metered exposures consistent is to compose the scene for flash, putting what needs to be correctly exposed in the foreground which the algorithms seem to assume will be the norm.
When I want absolute control I use M mode for camera and flash. It just as fast to adjust shutter as it is EC to arrive at the desired ambient exposure and the same is true for setting M power levels vs dialing in FEC. For things like a series of portraits on the same background an Av / ETTL exposures will vary and so will the background exposure shot-to-shot. With M once the exposure is set properly for highlight detail on one subject at a fixed distance from key and fill the exposure will remain same for all, regardless of complexion and clothing because correct digital exposure is based on highlight detail.
cgardner wrote:
Canon flash has constantly evolving, not particularly well documented technology.
Chuck,
What you're referring to are the changes in the way the flash is exposing the foreground. OP's question was about the change in metered EV in particular the increase in the shutter speed in camera's AV mode when hot shoe mounted flash is present.
My agrument is that in AV mode there is no change in the metered EV (given all other variables like metering mode or abmient exposure hold constant). Thus it does not matter which Canon flash is used, The metered EV value will not change and will be equal to the ambient exposure in the camera's AV mode.
The preceived change might have occured due to the inadvertant shift in either camera's shooting mode (from AV to P) or due to the change in metering pattern (e.i. evaluative vs. spot etc) or simply to the change in the conditions of ambient light.
I thought perhaps you were right, even though it makes no sense to me technically. -But I just tried it again. The 430EX absolutely causes a change in my 5D's shutter speed, when I'm shooting AV mode, and the 580EX does not.
There's no way that I'm imagining this. And besides, as I just wrote, the way my camera rects to the 430 seems CORRECT. How could it be otherwise? What you seem to be saying is, in Av mode the camera will choose a proper shutter speed based on ISO and F-stop, plus ambient light. Then, when I turn on a 580EX, the camera doesn't care, keeps the fast shutter speed, and over-exposes.
Well, that IS what's happening, but how can that possibly be correct?
I'm sure you know what you're saying, but I'm REALLY not understanding something here.
I don't question that the shutter in changing in Av mode differently with the 430ex and 580exII, but I don't see how that is a good thing. Maybe its a defective 430ex... I just checked my 580ex (older version) on my 20D in Av mode and the shutter speed does not change if I turn the flash on and off.
Shutter speed doesn't affect flash exposure so there is no logical reason turning on the flash should change the shutter speed. The auto-fill function under the older ETTL system changed flash intensity based on the EV level, not the ambient exposure. The auto-fill algorithm was based on the common practice of keeping the frontal light about a stop below the back rim-light when in bright sun. The face is actually underexposed, but doesn't look so perceptually because of the backlight. But as ambient level drops the perceptual balance of flash and ambient lit areas change and you'd need progressively more flash as the background gets darker make the face appear to be exposed normally. Its perceptual, how the brain thinks the face looks due to the overall contrast of the frontal and background lighting. The auto-fill algorithm just tried to anticipate and deliver light balance which looked "normal" (i.e. as by eye) in changing ambient lighting. But it was replaced by evaluative zone based metering with ETTL II.
I don't see why you think the shutter speed changing should be the norm when flash is activated. Lets say for example you are shooting a fill flash photo of the wife standing in front of the grand canyon in backlight. The only thing the flash will hit and reflect is her face and body.
The ambient exposure is, as always, Sunny 16, which adjusted for the x-sync limit of the 5D would be f/11 @ 1/200th. So if shooting in Av you'd set the aperture to f/11 and the camera would select 1/200th.
Since the background is so far away any additional light from the flash will not affect its exposure. Why would you want the shutter speed to change if the flash is turn on in that case?
What affects the exposure on the front of the wife is the flash duration (i.e. power level). Were you to measure the shady side of the face with an incident meter you'd find it was 3 stops below the sunlit side: there is always "Shady 5.6" on the sided opposite the Sunny 16. So all the fill flash need to do is raise the ambient about 2 stops so the face is perceived as it would be by eye, a bit less bright than the sunlit side.
In practical terms all that matters it that the exposure of foreground and background is correct. If the shutter shifts and takes the exposure the wrong direction when the flash is turned on, just compensate with EC like you would do in any Av shot.
p.1 #10 · 580EX II - doesn't adjust shutter speed?
Cableaddict,
As Chuck pointed out above, this is not 580 but 430 that behaves strangely in your case. Once again AV mode is designated for fill flash in Canon's E-TTL system and thus the presence or absense of the flash will have no bearing on total EV value as this is 100% ambient exposure. The camera then calculates the flash intensity needed to light the foreground correctly.
This is well documented in the literature as well as in the user manuals for both 430 and 580.
Here is a quote from the article I've referred to in my first post:
Av (aperture priority) and Tv (shutter speed priority) modes set the shutter speed or aperture to expose for the existing light conditions correctly. They then fill in the foreground using flash. If light levels are low you will need a tripod to avoid blur.
If you feel your 580 is overexposing play with your metering setting. Try spot vs. evaluative.
General advise from people using flash in AV mode is to set flash exposure comensation to -3/4. You can start from there and adjust exposure to your liking. I can't say much aboout this as I almost never use flash in AV mode.
The best use of flash in AV mode is during direct snlight or other contrasty lighting situations. For other situations I suggest to try using cvamera in M mode with evaluative metering. This will correctly expose your background. Then E-TTL will calculate the flash intensity so to correctly expose the foreground. In this case your main light source for the foreground becomes your flash not the ambient light.
p.1 #11 · 580EX II - doesn't adjust shutter speed?
VladKenner wrote:
Cableaddict,
As Chuck pointed out above, this is not 580 but 430 that behaves strangely in your case. .
Yes, Vlad. I understand that now, having had a chance to read the manuals & online Canon tutorials. Weird what my 430 is doing, (it's pne of the very early ones) but again I must say that to me it's the way it SHOULD be. It also seems clear than my 580 is defective. It does NOT work like the manual says it should.
Anyway, why doesn't Canon make an extra choice on the Speedlights, for AV mode, to purposely do what my 430 is doing? I love Av mode, so let the camera make shutter adjustments based on total light availanle, including the speedlight.
I mean, DUH. One could always choose the current "fill" function, or shoot manual, but what a convenient option to have.
Well, at least I understand now. I'm learning to shoot in full manual. Not so bad, really, and I can use a lot more light from the flash. In fact, I'm starting to think it was a mistake buying the 580EX as the 430 gives me more in manual mode than I was getting in Av.
p.1 #12 · 580EX II - doesn't adjust shutter speed?
Anyway, why doesn't Canon make an extra choice on the Speedlights, for AV mode, to purposely do what my 430 is doing?
Because as Chuck correctly pointed out you want to correctly expose the backgrond not lit by flash. Think about a picture of someone with the Grand Canyon on the background and you will understand what I mean. Again if you want your flash to be a primary source of light without going into manual mode then P is your choice. If both shutter speed and the background light is a concern and fill light is needed use Tv mode and the fastest available lenses.
