600EX-II exposure question...help!

[CapeCodDan]

Using this strobe on a 6DMII. As I understand it, the ETTL mode works well only when the camera mode is set to P.  However, P tends to set the aperture to 4.0; when I need more depth of field, I have to use AV mode.  Now in order to get auto exposure out of the flash - so I can walk around shooting different subjects in different rooms, say - I switch the flash mode to Ext.A. (I think I'm doing everything right so far, yes?)  However this is tending to underexpose by at least two stops, so I adjust the flash's exposure compensation accordingly, to, say, +2....which I arrive at by trial and error.  My question is: is this the way it's all supposed to work?   Why aren't I achieving properly exposed images without having to compensate?

[CapeCodDan]

All, thanks for your input.  I'm experienced with speedlites but trying to get to know the 600 better...just trying to make walkaround shooting a little more "user-friendly."  I want to be able to walk in and out of different rooms (say, in an office or home environment), shoot quickly with the flash head up or swiveled to bounce, and know my exposure on people's faces will be good. Of course I don't want to use P or Auto modes.  I've tried E-TTL in Av mode but got inconsistent results. So I tried Ext.A and it seemed more consistent but I had to use FEC at +2 to get a decent histogram.  Manual mode won't serve me well since every time I enter a room, I'll have to stop and adjust exposure for each room's environment.  I want to stay in Av, use a middle-aperture (say, 6.3, 7.1, 8.0 etc) to ensure a group of several people at slightly different distances will all be acceptably sharp.  All your advice suggests to stay with E-TTL so I will keep at it!

[amfoto1]

Sorry to be a couple weeks late to the party... I just saw this post.

You have incorrect information about how ETTL (or ETTL II) works. Some of the previous responses aren't asdetailed.as they could be, either.

ETTL/ETTL II provides "Flash Auto Exposure" (AE).... Much like Av, Tv, P and M with Auto ISO all provide various forms of AE without flash. In fact, ETTL makes for Flash AE in every camera exposure mode... even strictly Manual when it's used with flash.

The way it works is that ETTL fires a low powered (1/64) "pre-flash" which the camera uses to determine a "correct" flash exposure, which is then applied to a more full powered "real" flash exposure.

ETTL works differently depending upon how the camera is set, but it definitely is not correc that it "only works with P". It provides different types of Flash AE, but all are still auto exposures.

When the camera is set to ANY of the AE modes (Av, Tv, P... and possibly M w/Auto ISO), ETTL automatically acts as FILL FLASH, by default. The flash's power for FILL is set to -1.66 stops, in most cases. (In other words, if you dial up Flash Exposure Compensation by +1.66 stops, you should get the equivalent of "full flash", if that's what you want.) You should get pretty close to the same results regardless of the AE mode the camera is set to.... Av, Tv or P  (and probably M w/Auto ISO too, though I've never confirmed this.)

The only time ETTL defaults to FULL FLASH is when the camera is set to fully Manual exposure (M without Auto ISO).

All this assumes you are limiting the camera's shutter to its flash sync speed (probably 1/200 on a 6D Mark II). It also assumes not dialed in any Exposure Compensation (effecting how the camera treats ambient light) or Flash Exposure Comensation (effecting how the camera treats the flash's output). Both E.C. and FEC can be used to fine tune exposures to your preferences. 

Your flash has High Speed Sync, which allows shutter speeds faster than the cameras sync speed to be used. This shortens the duration of the flash output and greatly reduces the distance the flash can reach, so use it with care and keep it to a minimum. After all, the flash itself can act like a fairly fast shutter speed, approx. equiv. to at least 1/720 in most cases. In fact, with Full Flash, the short duration of the flash can be used to prevent "camera shake blur" and even freeze moving subjects nicely, regardless of the camera's actual shutter speed. (With Fill Flash or when slower shutter speeds are allowing a lot of ambient light in the mix, ghosting effects can result.... Your flash has a "2nd Curtain Sync" mode that can be used so that "ghosting" appears "behind" a moving subject and look natureal. With normal 1st curtain sync, the ghost will appear "ahead" of the subject, making them appear to be moving backwards.)

This all also assumes you're using direct flash... not bouncing it, which can cause all sorts of problems with consistency and color tints. Bouncing greatly increases the distance light has to travel, wastes a lot of light to "spill" and any bounce surface colorations can influence an image. If you wish to do bounce, I recommend getting a bounce card accessory to fit to the flash, for much better consistency.

Light modifiers, such as portable soft boxes or other diffusers, can be used to tone down direct flash in a more controlled and predictable manner. In most cases it also "wastes" less light than bounce (which can cause flash to be slow recycling and even lead to overheating if used repeatedly).

ETTL will work well with either Full or Fill flash. It's just a simple matter of selecting either M mode or your choice of the AE modes of the camera. You mention wanting to be able to set the aperture for depth of field effects, which can be done with Av AE or with M w/Auto ISO AE (probably), or with fully M mode.

When using Av with flash, the camera will default to shutter speeds no faster than the flash sync speed, unless you override it. Again, if you are looking for a more powerful flash effect, simply dial in +1.66 FEC. If you want the camera to increase or reduce how much ambient light is captured in each image, dial E.C. down or up. 

I really don't know how M w/Auto ISO works with flash, so you'll have to experiment. However, remember that M w/Auto ISO is actually another AE mode... it is no longer "manual", because the camera will adjust the ISO. If using this, you'll have to watch that ISO doesn't go higher than you'd like, and (at the other extreme) that  exposures aren't blown out at the lowest ISO.

Also rememver that "real" M.... M without Auto ISO... is also still an AE mode when used with ETTL flash. It's now Flash AE... so, no, you don't have to be constantly adjusting everything. So long as you use ETTL, the flash's output will be automatically adjusted to what the camera's metering system thinks is a "correct" exposure. You can control how much ambient light is included in images, by adjusting shutter, aperture and ISO yourself.

If you are getting inconsisten results in any of the AE modes, it may be due to the metering pattern you've selected (Evaluative, Center Weighted, Partial or Spot) and how you are effecting exposure with E.C. and FEC adjustments. Another reason for inconsistency is just like when shooting without flash... metering is reflective, so subject tonality effects exposure. A lighter than average subject causes the camera and flash to want to under-expose, while a darker than average one will cause it to over-expose. This is what E.C. and FEC are for. In my opinion, the smaller and more precise metering, the more careful you need to be with E.C. and FEC. If using Evalutive metering or Center Weighted, the entire image area is being measured. Evaluative goes a step farther and puts extra emphasis right aound the active AF point(s). Partial and especially Spot are measuring much less of the scene and more susceptible to variations in subject tonality.

Other responses mention using the camera's menu to set FEC. Personally, I use the dial right on the back of the flash instead. Quick and easy. The flash's LCD shows what you've set. Also, on most Canon EX with a display, notice near the bottom of the screen that the flash gives you an idea of it's minimum and maximum range, based upon the current flash and camera settings. I think in most flashes this can be set to display in feet or meters, based upon a Custom Function in the flash itself. Aperture and ISO have the greatest effect on flash distances, unless you use High Speed Sync and exceed the camera's sync speed. 

I have no idea what "Ext A" is. Another response suggests that's a special setting to use older flash on a newer camera... or older cameras with a newer flash. I'll take their word for it. With my Canon flashes, I mostly use ETTL or fully Manual at different power levels.

Learn to use and control ETTL. It makes flash photography easy!

The main thing to remember is:

1. ETTL + any AE mode = FILL FLASH.

2. ETTL + fully manual mode = FULL FLASH.

***********

Alan Myers
San Jose, Calif., USA
"Walk softly and carry a big lens."
GEAR: 5DII, 7DII (x2), 7D(x2) some other cameras, various lenses & accessories
FLICKR & ZENFOLIO 

[MikeSowsun]

The 580EX II and 600EX are both very similar in design and operation.

They both have the ability to shoot in 5 possible modes, all of which are all covered in the user manual:

1) Manual

2) E-TTL  (late film and digital era Through The Lens)

3) TTL  (early film era auto Through The Lens)

4) External Auto

5) External Manual

External metering uses an exposure sensor on the front of the flash instead of the Through The Lens metering inside the camera body. It is an “old school” method of metering that predates TTL film and ETTL digital. It is an option for those who don’t trust modern ETTL. 

[RobertTheFat]

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@amfoto1 wrote:

Sorry to be a couple weeks late to the party... I just saw this post.

You have incorrect information about how ETTL (or ETTL II) works. Some of the previous responses aren't as detailed.as they could be, either...

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Alan's is a longwinded explanation, but it's worth taking the time to read and understand it. As I mentioned in a previous post in this thread, Canon's manuals (at least the ones I've stumbled onto) don't do a good job of explaining the behavior of the E-TTL algorithm. I think Alan's post does.