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Thread started 11 Dec 2013 (Wednesday) 23:40
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70D bounced flash exposure bug (testers needed)

 
bobn4burton
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Dec 11, 2013 23:40 |  #1

I started a thread on dpreview forums about a problem I was seeing with my new 70D where I'd get serious under-exposure when using a bounced flash. Still early on, and fairly limited testing, but this is starting to appear like a pretty widespread 70D problem. So I'm looking for more people with 70D's to test and post back so that we can get a better idea of how widespread this problem is...and hopefully get Canon to address it in a future firmware update. You can read the whole thread here if you'd like:

http://www.dpreview.co​m/forums/thread/358417​8 (external link)

But I'll provide a quick/executive summary of what we've found so far:

  • Most 70D bodies appear to have this problem, although there are 1 or 2 people that it appears don't suffer from this problem
  • When bouncing the flash relying on ETTL/ETTL-II for flash exposure, resulting pictures are 1-2 stops under-exposed
  • To see this problem, you really need a fairly dark room...ensuring the flash is the primary source of light
  • The lens affects the degree of under-exposure. The slower the lens, the worse the under-exposure. (i.e. f1.8 lenses actually do pretty well, f3.5-5.6 lenses result in 1-2 stops under-exposure and f4.0 lenses are in the middle)
  • We've been testing in all camera modes so far and the problem persists through all modes (even in fully automatic green box mode)
  • If using FEL before taking the picture, exposures turn out great. So this problem only affects exposure algorithms used for pre-flash exposure metering when using only the shutter button.
  • I have personally tested 9 total canon dslr bodies. Xsi, T4i(x2), T5i, 70D(x3), 5Dm3, 1Dm3. The three 70D bodies all showed this problem. All 6 of the other bodies gave pretty good to great results.
  • I have also tested with three different flashes, and it appears the problem is independent of flash so far.
  • You can fix the exposure by dialing in additional FEC, but this shouldn't be needed for general use and is what ETTL/ETTL-II is supposed to take care of (which is does fairly well on other bodies)
I'm sure I've missed more details which you can find by referencing the above linked thread or just asking here. But I'm hoping I get can some more 70D owners from this forum to test and report back their results. I haven't contacted Canon support yet because I wanted to gather as much data/documentation as possible first.

BTW, I completely love this camera BTW. Video is amazing...and just an all-around great camera. I do tend to take a lot of pictures of my kids indoors with bounced flash...so this is the only problem I have with the camera. I can work around the problem by using FEL or dialing in some FEC, but that just takes extra time and makes it harder to get candid shots of my kids...



  
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EOS5DC
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Dec 12, 2013 10:04 |  #2
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Wow, two new guys. I have been using a flash since the Nixon administration. I have been using Canon flashes (580EX II, 550EX, 430EX II) for about four years. I have never found the Canon flash system, or the Canon optically-fired flash control system, wanting. That proves ZERO, but it does give some credence to the criticism to follow.

FYI, I read the entirety of the first two pages of the DPR forum.

You are getting underexposure when bouncing. It is worse with smaller apertures. You get better results with wider apertures. That points to user error. A bad flash would be consistently bad. If your flash metering system were judging 2 stops less than needed, it would always be 2 stops, not worse with smaller aperture.

You tested several 70Ds and several flashes. You got the same results. That points to user error. What do you think is more likely, 3 faulty 70D bodies, several faulty flashes, poor design nobody else noticed, or user error?

You mentioned doing all of this in GREEN-BOX full-auto. That points to user error, and agrees with the whole aperture thing above. I believe that GREEN-BOX is limited to ISO 400 when using flash. That could be a source of the problem. I find ISO 400 an absolute minimum, in the best of conditions, when using bounce flash. I generally shoot on-camera bounce at 800 or 1250.

You mentioned having the Auto-Lighting-Optimizer turned on in some of the testing. I don't even think that works in GREEN-BOX. If it does, or if you used ALO when not in GREEN-BOX, you can count on erratic flash exposure. This, once again, points to user error.

One thing I did not see in your DPR write up was any mention of the Flash Exposure Confirmation light. A properly working Canon flash should tell you whether or not it was able to obtain a good exposure.

I would suggest to following:

First shot:
Set the camera to Manual mode. Turn ALO off. Leave it off. Forever. Select 1/250 (or whatever max sync-speed is), f/8 and ISO 3200. Set the flash to ETTL. Choose a subject with NO shiny reflective surfaces, these can fool the FE system. Bounce off a wall or ceiling that is with ten feet of the camera and 10 feet of the subject. Dial in 1/2 or 2/3 of +FEC. You should get near-perfect results, exposure-wise.

Successive shots:
EXACT SAME CAMERA SETUP AND SUBJECT. Put the flash into MANUAL mode, 1/1 (full-power). My guess is this shot will be hugely overexposed. Decrease ISO until you get underexposure. My guess is you will start to get underexposure near ISO 800, at ISO 100 it will be severe.

If you get the predicted results from these trials, rest assured that there is nothing wrong with your camera, or the flash. I really hope this helps diagnose the problem. And yes, it is still possible that your camera and/or your flash is faulty. I just don't think you've established that, yet.


Bodies: 60D, 6D.
EFs: 15-85, 10-22
EF: 28-75, 35 f/2 IS, Σ70-200 OS, 100-400L
Flash: 580EX II, 430 EX II

  
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bobn4burton
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Dec 12, 2013 11:10 |  #3

First...thank you for taking the time to reply and provide your feedback. However, some of your logic eludes me...

EOS5DC wrote in post #16521637 (external link)
FYI, I read the entirety of the first two pages of the DPR forum.

If interested in all the details you'll need to read more than that. That thread was and is an evolution.

EOS5DC wrote in post #16521637 (external link)
You are getting underexposure when bouncing. It is worse with smaller apertures. You get better results with wider apertures.

Not entirely true. Performance is independent of the aperture SETTING. What does affect performance is the max aperture of lens used. Faster lenses seem to perform better than slower lenses. I have a possible theory on this, but still have some additional testing to do first.

EOS5DC wrote in post #16521637 (external link)
A bad flash would be consistently bad.

I ruled out my flash being defective fairly early on.

EOS5DC wrote in post #16521637 (external link)
You tested several 70Ds and several flashes. You got the same results. That points to user error. What do you think is more likely, 3 faulty 70D bodies, several faulty flashes, poor design nobody else noticed, or user error?

Actually that points to two likely possibilities. User error or a possible bug/defect with the camera body series. I agree that user error is MUCH more likely and have stated so several times. That's the reason I'm trying to get others to test. So far there are quite a few people on DPR thread that are seeing the EXACT same problem...which is beginning to lend credence to a possible firmware bug or fairly widespread defect/problem on the 70D body. I (and others) have done enough testing by this point to pretty much eliminate any type of 'one-of' hardware defect. This is either user-error or a widespread problem.

EOS5DC wrote in post #16521637 (external link)
You mentioned doing all of this in GREEN-BOX full-auto. That points to user error, and agrees with the whole aperture thing above.

Again...your logic completely eludes me here??? How on earth does using green-box full-auto mode point to user error??? That's the whole point of green-box mode...it eliminates user error. Please enlighten me on what settings I could have changed to improve results in green-box mode...?? Oh yeah, there are really none. The camera and all its internal algorithms pretty much do EVERYTHING for you.

So when I take several dslr bodies, set them all to green-box mode. Then one by one, set them on a tripod, maintaining the same lens/flash gear on each and take the same framed picture and I see all non-70D bodies give very good exposures with bounced flash and all 70D bodies are significantly underexposed...

Please tell me what I could have done different, as a user, to change these results?

EOS5DC wrote in post #16521637 (external link)
You mentioned having the Auto-Lighting-Optimizer turned on in some of the testing.

You have me mixed up with another user that was playing with this setting during his testing.

EOS5DC wrote in post #16521637 (external link)
One thing I did not see in your DPR write up was any mention of the Flash Exposure Confirmation light.

You are correct, I will double check this tonight. You are referring to the led on the back of the flash and that it should turn green with proper exposure aquisition?

EOS5DC wrote in post #16521637 (external link)
I would suggest to following:

...

If you get the predicted results from these trials, rest assured that there is nothing wrong with your camera, or the flash. I really hope this helps diagnose the problem. And yes, it is still possible that your camera and/or your flash is faulty. I just don't think you've established that, yet.

I will try your suggested test tonight and report what I find.

Again...please know that I have been suspect of user-error from the beginning. But I've been using bounce flash with my 430exII and T4i (and Xsi previous to T4i) for the last 6 or 7 years and have always gotten pretty good results. I typically shoot in Tv or Av mode...but will venture across the board from green box to manual. I usually don't use the flash in manual mode...but let ETTL take care of all flash power adjustments. I've always gotten great results. Then as soon as I get my 70D and start bouncing flash...I get 1-2 stop under exposures for all bounced flash using ETTL.




  
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apersson850
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Dec 12, 2013 11:17 as a reply to  @ bobn4burton's post |  #4

Not that it seems to matter here, but ALO is implicit in the green box mode.

When I first read about this I too thought that the flash wasn't powerful enough when you bounced, since you loose equivalent to 2-4 f-stops, but that doesn't explain why it works if you use FEL. The flash isn't more powerful just because you use FEL. That would instead indicate that the normal E-TTL evaluative metering is being fooled by something, which FEL is not.

Now I've not read the whole tread at DPR, but have you tried evaluative vs. average flash metering modes?


Anders

  
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bobn4burton
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Dec 12, 2013 11:33 |  #5

apersson850 wrote in post #16521809 (external link)
Now I've not read the whole tread at DPR, but have you tried evaluative vs. average flash metering modes?

Yes. Setting to average tends to give slightly better results than evaluative...but shots are still too under-exposed.




  
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Wilt
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Dec 12, 2013 11:42 |  #6

Back in the days of the 20D and 30D, it was routine that folks would need to almost perpetually dial in FEC = +1 in order to have a well exposed shot with ETTL flash. Well documented by many on POTN threads back then. Then, magically, when I got my 40D that need for FEC went away! Perhaps the 70D just returns to the 'good old days' (good?...yeah right!) of the 20D/30D

Shot with 20D with FEC = 0

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EOS5DC
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Dec 12, 2013 12:29 |  #7
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OP, you are correct. I could have learned more by finishing the entire thread. Sorry. One comment about GREEN-BOX mode. I mentioned user error in that context because even GREEN BOX can't do something the camera is incapable of. If stopping down requires flash output that your flash is not capable of, you will get underexposure. GREEN BOX can certainly do a lot of things reasonably well. It can't allow you to exceed the physical limitations of your equipment. Again, I don't know that is the problem. It is just a suggestion.

FWIW, on my 5D, the default FEC is ALWAYS at least +2/3, no matter the P,Av,Tv, M setting. Zero FEC results in underexposure every time. That said, it is fairly consistent, not like your issue. I think Canon cameras tend to underexposed indoor flash all the time. You may just have an extreme example on your hands. Good luck with your testing. Let us know how things work out.


Bodies: 60D, 6D.
EFs: 15-85, 10-22
EF: 28-75, 35 f/2 IS, Σ70-200 OS, 100-400L
Flash: 580EX II, 430 EX II

  
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bobn4burton
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Dec 12, 2013 12:40 |  #8

Wilt wrote in post #16521870 (external link)
Back in the days of the 20D and 30D, it was routine that folks would need to almost perpetually dial in FEC = +1 in order to have a well exposed shot with ETTL flash. Well documented by many on POTN threads back then. Then, magically, when I got my 40D that need for FEC went away! Perhaps the 70D just returns to the 'good old days' (good?...yeah right!) of the 20D/30D

Wonderful...if this turns out to be a widespread 70D thing...I was kinda hoping that sometime in the next 6 months or so that Canon might address the issue with a firmware update. It appears that probably won't be happening if they never fixed this type of issue on older bodies...

:cry:




  
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Wilt
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Dec 12, 2013 12:47 |  #9

I would not jump to conclusions yet. Flash testing has so many variables, so I would discount the testimony of relative newcomers to ETTL, and put much more faith in the findings of Canon ETTL veterans.


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EOS5DC
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Dec 12, 2013 15:01 |  #10
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I don't have a 70D, but I have lots of experience with Canon flash. Fortunately, I have lots of time on my hands. If you want me to try something specific, just ask. I never turn down a chance to learn something new.


Bodies: 60D, 6D.
EFs: 15-85, 10-22
EF: 28-75, 35 f/2 IS, Σ70-200 OS, 100-400L
Flash: 580EX II, 430 EX II

  
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bobn4burton
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Dec 12, 2013 16:47 |  #11

EOS5DC wrote in post #16522353 (external link)
I don't have a 70D, but I have lots of experience with Canon flash. Fortunately, I have lots of time on my hands. If you want me to try something specific, just ask. I never turn down a chance to learn something new.

If there was anyway you could get your hands on a 70D...then we could definitely use more data points. With your extensive background using Canon flash, you'd be a super good data point to help disprove or validate the results we've been seeing.

Heck...even if the next time you were at a local camera store that had a 70D on demo, you could just throw your flash on it quick and try a few test shots. I did this at my local camera shop and they were super helpful...even let me take the camera back into their photo-taking room where I could get ambient conditions pretty dark.

So far, results have been consistent enough that the test setup is fairly easy. Just need a pretty dark room, then take a few shots with bounced flash and see how they expose. Subject should be about 10-15 feet away and most hots have been about 50mm zoom level.

Shots should be consistently 1-2 stops underexposed for any mode (P, Tv, Av, M as well as green box mode)...but you have to use a slow lens, like an f3.5-5.6 or f4-5.6.




  
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EOS5DC
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Dec 12, 2013 17:37 |  #12
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bobn4burton wrote in post #16522650 (external link)
If there was anyway you could get your hands on a 70D...then we could definitely use more data points. With your extensive background using Canon flash, you'd be a super good data point to help disprove or validate the results we've been seeing.

Heck...even if the next time you were at a local camera store that had a 70D on demo, you could just throw your flash on it quick and try a few test shots. I did this at my local camera shop and they were super helpful...even let me take the camera back into their photo-taking room where I could get ambient conditions pretty dark.

So far, results have been consistent enough that the test setup is fairly easy. Just need a pretty dark room, then take a few shots with bounced flash and see how they expose. Subject should be about 10-15 feet away and most hots have been about 50mm zoom level.

Shots should be consistently 1-2 stops underexposed for any mode (P, Tv, Av, M as well as green box mode)...but you have to use a slow lens, like an f3.5-5.6 or f4-5.6.

All we have nearby is BestBuy. The closest Canon shop is in Chicago, over 100 miles from me. Just in case, what ISO are you shooting?

This is a wild shot. Just guessing. Do you have FEC enabled on the flash itself. If it is set on the flash, you can't do anything with FEC on the camera. On second thought, not much of a guess. You did say +FEC helps, right?


Bodies: 60D, 6D.
EFs: 15-85, 10-22
EF: 28-75, 35 f/2 IS, Σ70-200 OS, 100-400L
Flash: 580EX II, 430 EX II

  
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mayt444
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Dec 12, 2013 18:45 as a reply to  @ EOS5DC's post |  #13

I have a 70D and just ordered a YN-565EX that should be here tomorrow. I did notice my old Sigma flash under exposed when bounced with the 70D. I am no flash expert but willing to pass on any results I observe.
Clay


Clay
Canon 70D, Canon G12 , Tamron SP 150-600mm Di VC USD, Sigma 17-70mm F2.8-4 DC Macro OS HSM C, Canon 18-55 IS STM, 55-250 IS, Canon 50mm 1.8 II.

  
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huntersdad
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Dec 12, 2013 18:55 |  #14

Mentioned on FM, I have noticed the same with both my 6d and 70d. Both are about .75-1 stop underexposed. Not a big deal once you figure it out, just dial in some FEC.


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EOS5DC
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Dec 12, 2013 19:31 |  #15
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huntersdad wrote in post #16522897 (external link)
Mentioned on FM, I have noticed the same with both my 6d and 70d. Both are about .75-1 stop underexposed. Not a big deal once you figure it out, just dial in some FEC.

That is exactly my experience with Canon ETTL. It is consistent, though. The OP is having an intermittent and variable problem.


Bodies: 60D, 6D.
EFs: 15-85, 10-22
EF: 28-75, 35 f/2 IS, Σ70-200 OS, 100-400L
Flash: 580EX II, 430 EX II

  
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70D bounced flash exposure bug (testers needed)
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