# Accurate auto flash exposure impossible for 5D MKlll ?



## rlarsen (Oct 22, 2015)

Is there a speed light on the planet that provides reliable auto-exposure for the Canon 5D MKlll ?

The Canon 580EX I use is not at all reliable for auto exposure. Is there a speed light that works well, or even a little better ?

2015 and still no decent Canon speed light technology ?


----------



## Zeidora (Oct 22, 2015)

What are your problems? Accuracy or precision? 
I've noticed in manual mode occasional deviation of about 1/3 f-stop between successive shots of same setting. That seems to be the intrinsic variance of flash out-put. About one in 20-30 is noticeable off. I see it in z-stacking with up to about 200 successive frames. 

How do you meter? With evaluative metering, it is a crap shot. Don't like it for available light, for flash it is a disaster, because there is no way of understanding the algorithm and to predict the outcome even with the slightest changes in composition or settings. Center weighted average is reasonably predictable, and by understanding neutral grey and inverse square law, you can pre-visualize the results and do flash exposure compensation. With a bit of practice, you get it down to +/- 1/2 f-stop on first shot, so well within RAW file adjustments. 

Hope that helps.


----------



## rlarsen (Oct 22, 2015)

Thanks for your reply.
Accuracy or precision ? That's like my car GPS asking shortest or fastest ? 

My goal is to use the flash on auto and get reasonably good exposures. 

Your suggestion of metering pattern selection is interesting. Are you suggesting setting the camera body to center weighted metering ? I always use matrix.

I appreciate all help !!

Rex

www.rexlarsen.com


----------



## Zeidora (Oct 22, 2015)

Accurate = close to intended.
Precise = same intensity when repeating same shot.

I suspect matrix metering is your first culprit. 
Do you understand neutral grey and inverse square law?
Neutral grey is what the camera metering system expects. In flash photography, often significant areas of the image are much darker. To avoid overexposure of the foreground, you need to use minus correction on flash exposure compensation.
Inverse square law: the light intensity is reduced by the square of the distance. If you have a foreground at 1 m and a background at 2 m, The background is underexposed by factor of 4 = 2 f-stops. 

These two elements need to be combined: estimate amount of fore or back ground, estimate how far background is separated from foreground then correct for neutral grey assumption of metering system.
If half is foreground and that foreground is more or less neutral grey, half is background at infinity distance (= pitch dark), adjust flash exposure compensation to -1. If NG area is 1/4 of frame, then use -1.5. 

This is not perfect, but will get you 80-90% there, within +/- 0.5 f-stops. I assume you use on-camera flash.
If you want to be really precise, get an external flash meter, and use flash in manual mode. That is how I shoot LF flash (Sekonik 558L), with flash on PC sync cord. 

Matrix metering uses a number of image elements, and depending exactly where which fore/back-ground element is positioned, and the weighting algorithm, you get different results. It aims to give decent results for "normal/typical" scenes, but is useless and temperamental when you do something a bit different. Can't stand it. It works ok-ish for daylight, because differences in illumination level for various elements is not too far off. But flash accentuates those brightness differences, hence, results tend to be disasters.

All the above is for 100% flash illumination. In mixed lighting or for fill flash it gets a bit more involved.


----------



## rlarsen (Oct 22, 2015)

I appreciate all help and suggestions.

Quite simply, I'm frustrated that TTL flash is such a weak part of the Canon system. I've seen much better auto flash performance in a variety of point and shoot cameras. With the camera knowing the distance of focusing point to camera I wouldn't think in 2015 that TTL exposure accuracy remains such an issue that some photographers use their flash in manual to avoid inconsistency.

As a long-time pro I have several hand-held meters and often use manual exposure with my five studio strobes and five Canon speed lights. That approach would not be practical for run and gun event coverage that I need TTL flash for.

I'm eager to know if there is any brand and model of speed light that provides improved TTL performance over my Canon 580EX. Any offer of camera or flash settings that can improve my results are welcome as well.


----------



## arthurbikemad (Oct 22, 2015)

I may not be able to give much advice other than saying my 600 EXRTs give me great results with TTL when on the run, outside I use TTL for fill and even inside the results have been ok. I also use a 308S in manual mode if I shoot studio style shots, I run four 600s and the STE3RT, I would have to say shooting mixed TTL and manual, TTL ratios etc etc I have been very pleased.


----------



## unfocused (Oct 22, 2015)

arthurbikemad said:


> I may not be able to give much advice other than saying my 600 EXRTs give me great results with TTL when on the run...



I'm perplexed too. I have had great results with TTL, first with the 580 EX II and now with 600 EX RTs. Face it, flash is not an exact science. Now, it may be just the frame of reference. I started shooting in the stone age when everything was a guesstimate and you had to wait until you developed your film to see if it worked.

Looking at your portfolio, you are obviously getting great results, what's the problem?


----------



## pwp (Oct 23, 2015)

Consistent speedlight exposure can be a frustrating thing regardless of your experience level. TTL or ETTL is useful but not a one-size-fits-all magic bullet. It takes skill and experience to get the best out of it. 

There are infinite possible variations that can influence ETTL flash exposure. ETTL is smart up to a point, but can't distinguish between obvious fail-points like a black wall behind a white subject. ETTL will read the scene tonally and attempt to deliver a mid-tone. So against black you'll likely get over-exposure. The inverse is true shooting a dark subject against white...you'll likely get under-exposure. You'll sometimes get extreme under-exposure if you're in direct line with a window or mirror in the background, or a prize winner with a shiny/reflective trophy. 

Most of the time you'll get good ETTL exposures with a 580EX, 580EX-II or 600EX-RT. It doesn't take more than a moment to check exposure and make the required adjustment. If ETTL just can't handle the situation, flick over to manual. If you've been getting consistent under-exposure, it could be you're expecting too much from your 580's output if you shoot at small apertures. At indoor events where I'm shooting with flash I'll typically shoot between f/4 and f/5 at 800 or 1600 iso. This has the multiple benefits of extending battery life, keeping recycle times short & holding the background exposure to some degree. 

There's nothing inherently wrong with the 580EX-1, it's a great flash. On just about every Canon flash I've owned, leaving exposure compensation on zero usually delivers under exposure. My default tends to be +1/3 to +2/3. At events I'd be adjusting flash exposure constantly to match the conditions. It's also entirely plausible that your 580EX-1 is faulty. It's quite an old flash now and may be delivering errors. Hope you get it all figured out.

-pw


----------



## privatebydesign (Oct 23, 2015)

pwp said:


> There are infinite possible variations that can influence ETTL flash exposure. ETTL is smart up to a point, but can't distinguish between obvious fail-points like a black wall behind a white subject. ETTL will read the scene tonally and attempt to deliver a mid-tone. So against black you'll likely get over-exposure. The inverse is true shooting a dark subject against white...you'll likely get under-exposure. You'll sometimes get extreme under-exposure if you're in direct line with a window or mirror in the background, or a prize winner with a shiny/reflective trophy.


Generally that is not what ETTL is doing, the pre flash is attempting to find the subject within the frame, hencee the numerous metering zones and auto switching to matrix metering, the flash will then try to give a midtoned subject exposure via aperture, flash power and iso, meanwhile the rest of the scene will be given a mid tone exposure via aperture, iSo and shutter speed, assuming you are in P, Tv, or Av. If you are in camera M and ETTL your M values will create the ambient, scene, exposure and the flash will still give subject mid tone unless you dial in flash exposure compensation.

With Canon cameras exposure compensation while using flash does not impact the subject exposure, only the ambient exposure. Flash exposure compensation only adjusts the metered exposure value for the subject.

Most people who have issues with ETTL don't fully understand what it is trying to do, when you do it makes sense and works very consistently.


----------



## rlarsen (Oct 23, 2015)

Again, I appreciate the exchange of ideas here and the kind words about my website portfolio. As a pro my job is to deliver quality images whether or not it is easy. I have good working knowledge of exposure compensation and use it all day long on my 5D bodies and speed lights. The more I need to use exposure compensation the more I am distracted, and missing shots due to exposure error with my camera or flash. 

In my experience Canon has a reputation for challenging auto flash exposure reliability. Some Canon shooters I know use manual exposure for this reason. Canon recently announced it would re-design its flash system then later followed up saying it would not come as soon as stated. I'm pleased that some of the posters here get satisfactory results or don't mind using a lot of exposure comp or manual settings.

I don't mean to belabor this conversation but wonder if people have found improved results with Canon flashes newer than my 580 EX, or other brands. If anyone has used the 580 then upgraded to the 580ll, 600EX-RT, or another brand and got improved results I would appreciate hearing about.

Thanks a lot

Rex
www.rexlarsen.com


----------



## privatebydesign (Oct 23, 2015)

And again, the only people I know who have issues with any TTL flash metering system, Canon, Nikon etc, are those that don't fully appreciate how it works.

I am not belittling your experience, just pointing out that at the level you are working not having an explicit understanding of how each flash is contributing to the subject metering is a recipe for dissapointment. The extensive use of too hot rim lights in your portfolio is an indicator that you are not fully aware of what those specific lights are being told to do. 

Also, we are not talking about Exposure Compensation, well we shouldn't be, we should be talking about Flash Exposure Compensation, FEC. EC and FEC work very differently on Canon and Nikon systems and are a cause of much confusion, in reality the Canon system gives you a lot more control, but if your subject is getting too much flash adjusting EC down will make it look worse because your background will go darker making the subject appear even lighter!

To be sure, all TTL digital metering systems, both flash and ambient exposure, are metering for 12% grey, or 1/2 stop below midtone. If your subject is not 12% reflective then any TTL metering system from any company is going to need compensation.

As for specific flashes getting better results, there is no doubt that if you have a 2012 camera body the 430EX-III RT and 600 -EX-RT give a greater degree of control, particularly in the ease in which you can mix flash modes in Group Mode.

But the truth is the key to getting consistent results with any TTL flash metering system is a very detailed understanding of what it is trying to do.


----------



## pwp (Oct 23, 2015)

rlarsen said:


> If anyone has used the 580 then upgraded to the 580ll, 600EX-RT, or another brand and got improved results I would appreciate hearing about.


Having owned and literally worn out 550, 580, 580II and now working with 600EX-RT I can't say I'm aware of any meaningful variation in exposure accuracy between them. None of them have been consistently fabulous. I haven't had direct Nikon experience since 2002, but many say that exposures with Nikon speedlights deliver a higher keeper rate. 

Privatebydesign has a better technical grasp and explanation of how ETTL works and you should defer to his explanation. I just know how to deliver results under pressure, learned by daily experience. FWIW I do use FEL fairly successfully in situations where I'm getting otherwise bad exposures.

-pw


----------



## rlarsen (Oct 23, 2015)

Thanks, PWP !

Sounds like your experience is typical and similar to mine, and we both clearly understand the difference between EC and FEC. Metering at 12%, 1/2 stop below mid-tone is a new one on me. If it was as simple as a half-stop correction for more consistent and accurate exposures I wouldn't be searching for a better speed light.

At the end of the day I can sort of make it work but it's a hassle and not much fun. ….and not much of an improvement over the Vivitar 283 in the 80's and 90's. A lot of chimping and correcting. 

I don't want to switch to Nikon for improved flash exposure but it's always been tempting.

Rex


----------

