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Archive 2008 · 40D and the MT-24EX Flash Metering Problem
  
 
Dalantech
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p.1 #1 · p.1 #1 · 40D and the MT-24EX Flash Metering Problem


Early this year I switched from using Canon’s Xti to the 40D and at the same time I was working on getting better diffusion from the MT-24EX. Oddly enough I was having exposure problems with the 40D that I never saw with the Xti: Scenes that the Xti would normally under expose by 1/3 of a stop the 40D would over expose by that same 1/3 of a stop or more. If I took six frames of a scene none of them would be exposed the same and they’d all be over exposed even though it’s normal for me to shoot with the MT-24EX set to -2/3 FEC.

Even shooting against something reflective would give me over exposures even though the camera should have under exposed. At first I thought the 40D was “hyper accurate” and that there was something wrong either with my technique or the diffuser materials that I had used on the twin flashes but as time passed I read more and more people make the same claim –the MT-24EX just doesn’t work well when attached to the 40D. The problem will manifest itself the most when you are shooting a subject when there is very little in the background for the flash to reflect off of –if the background is black in the final image then odds are the subject is completely blown (a problem that I never had with the Xti).

SteB, one of the posters at DP Review mentioned having the same exposure problem that I was seeing and that it seemed like the MT-24EX was operating in Average E-TTL mode instead of Evaluative. Sure enough switching the 40D to Average E-TTL mode seems to give the same exposures as Evaluative in my informal field testing. The work around that I eventually come up with is to make sure that the flash heads were pointed right at the scene I was shooting and to keep one flash head off centered from the top of the lens at the 11 O’clock position and place the other at 2 O’clock (relative to me). The angle of the heads depends on what you’re using for a diffuser –currently I’m using a pair of Sto-Fens over a piece of diffuser plastic that only blocks 2% of the light coming out of the flash. So I position the heads one click up from all the way down at life size and all the way down toward the lens for 2x to 5x shooting.

I’m still not getting consistent exposures, but it’s better than putting one of the flash heads at the very top of the MPE-65mm: It seems like one side of the subject gets thrown into too much shadow so the light meter over compensates for it –badly. If you see some insects with two sets of eyes and eight sets of wings it’s my fault cause the MT-24EX pumped out so much power it altered the critter’s genetics…

I contacted Canon on this issue and they responded to me very quickly –but their solution was for me to send all of my kit into a Canon service center. Unless they test my rig against the same scenes I shoot then they’re not going to see the problem and besides it not just a problem with my camera or flash…

So here's what I need you to do: If you shoot macro with the 40D and the MT-24EX then please respond to this thread and tell me if you are getting consistent exposures or not. If you are then please tell me a little about your technique and the types of scenes you shoot. If enough people post then maybe we can get Canon to take a serious look at the 40D's light meter...



Sep 14, 2008 at 02:39 PM
Corax
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p.1 #2 · p.1 #2 · 40D and the MT-24EX Flash Metering Problem


Using 40D with 24EX. Also noticed overexposure issues when compared to 10D. 'Solution' here is to set 24EX to -1 2/3 or so and things come out well enough that PS can rescue most shots. Have noticed that sequences of same shot (usually shoot 3 or 4) come out exposed differently by about 1 or so stops. Hmmm.



Sep 14, 2008 at 06:35 PM
Dalantech
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p.1 #3 · p.1 #3 · 40D and the MT-24EX Flash Metering Problem


Corax wrote:
Using 40D with 24EX. Also noticed overexposure issues when compared to 10D. 'Solution' here is to set 24EX to -1 2/3 or so and things come out well enough that PS can rescue most shots. Have noticed that sequences of same shot (usually shoot 3 or 4) come out exposed differently by about 1 or so stops. Hmmm.


Thanks for letting me know!



Sep 15, 2008 at 05:08 AM
The1
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p.1 #4 · p.1 #4 · 40D and the MT-24EX Flash Metering Problem


so it's 40D only you think? i have a 30D and a 5D i have just bought a mt-24ex so it's on the way to me now, if it's a 40D specific problem i wonder if they fixed it in the 50D, for now we know it's not a flash problem.


Sep 15, 2008 at 06:25 AM
stits
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p.1 #5 · p.1 #5 · 40D and the MT-24EX Flash Metering Problem


Can you though up some examples? I shoot with a 20d and a 1d III and think I've encountered what you're talking about to a lesser degree.


Sep 15, 2008 at 06:38 AM
Dalantech
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p.1 #6 · p.1 #6 · 40D and the MT-24EX Flash Metering Problem


The1 wrote:
so it's 40D only you think? i have a 30D and a 5D i have just bought a mt-24ex so it's on the way to me now, if it's a 40D specific problem i wonder if they fixed it in the 50D, for now we know it's not a flash problem.


Seems to be 40D only -but it might effect the 50D...



Sep 15, 2008 at 07:51 AM
Dalantech
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p.1 #7 · p.1 #7 · 40D and the MT-24EX Flash Metering Problem


stits wrote:
Can you though up some examples? I shoot with a 20d and a 1d III and think I've encountered what you're talking about to a lesser degree.


I'll have to go through my archive later and post some unedited JPGs from RAW so you can see what I'm seeing.



Sep 15, 2008 at 07:52 AM
Eyvind Ness
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p.1 #8 · p.1 #8 · 40D and the MT-24EX Flash Metering Problem


-So here's what I need you to do: If you shoot macro with the 40D and the MT-24EX then please respond to this thread and tell me if you are getting consistent exposures or not.


Good initiative! I no longer shoot with the 40D and MT24EX, but I gave up exactly for this reason. I now shoot with the 5D only.

And the trouble with giving examples, is that these shots were often immediately discarded, as there was no hope for a post-processing rescue operation (hopelessly over-exposed).



Sep 15, 2008 at 08:29 AM
Daemonoropsis
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p.1 #9 · p.1 #9 · 40D and the MT-24EX Flash Metering Problem


Hi John

saw this thread and would like add my support for getting canons attention to this problem

I shoot macro with a 40D mt-24ex and mp-e65 with almost random exposures. Until now I thought that i had maybe gotten a bad copy, I hope this is something that can be fixed with a firmware update or something.

I have used a 350D instead of the 40d before with no exposure problems




Sep 15, 2008 at 08:46 AM
Dalantech
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p.1 #10 · p.1 #10 · 40D and the MT-24EX Flash Metering Problem


Eyvind Ness wrote:
-So here's what I need you to do: If you shoot macro with the 40D and the MT-24EX then please respond to this thread and tell me if you are getting consistent exposures or not.

Good initiative! I no longer shoot with the 40D and MT24EX, but I gave up exactly for this reason. I now shoot with the 5D only.


Thanks!

Eyvind Ness wrote:
And the trouble with giving examples, is that these shots were often immediately discarded, as there was no hope for a post-processing rescue operation (hopelessly over-exposed).


I think I can dig up some shots that I "rescued" but process them as the camera metered the scene.



Sep 15, 2008 at 08:46 AM
 

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Tim Dollear
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p.1 #11 · p.1 #11 · 40D and the MT-24EX Flash Metering Problem


John, you already know this but I recently switched to the 30d with my flash and it works much more consistently. Thanks!


Sep 15, 2008 at 12:21 PM
SteB
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p.1 #12 · p.1 #12 · 40D and the MT-24EX Flash Metering Problem


My experience has been the same. I did the same thing Dalantech describes - that is switching betwee E-TTL evaluative and average metering. In both cases the exposure pattern (including over-exposure) was the same. In my experience evaluative TTL flash not just on Canon, but on all the systems I have used or tried works in a similar way. There is a tendency to under-exposure in tricky lighting. Normally serious over-exposure is rare with evaluative metering as the intention appears to be to save the highlights.

Unfortunately as the 40D is my first Canon DSLR I don't have any experience of using the MT24EX on another Canon DSLR body for comparison. However, when I use the 430EX on a bracket and off camera chord for macro shots I do not get the same over-exposure problems with the 40D and it behaves as I would expect an evaluative metering system to behave.

Incidentally, my solution when using the MT24EX on the 40D is to use the flash exposure lock (FEL). That is I point the circle in the viewfinder at a neutral tone and fire the pre-flash with the FEL button on the camera body. The problem is that this reading is only stored for I think 20 seconds.



Sep 15, 2008 at 01:54 PM
Dalantech
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p.1 #13 · p.1 #13 · 40D and the MT-24EX Flash Metering Problem


Tim Dollear wrote:
John, you already know this but I recently switched to the 30d with my flash and it works much more consistently. Thanks!


Thanks for the post Tim!



Sep 15, 2008 at 05:08 PM
Dalantech
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p.1 #14 · p.1 #14 · 40D and the MT-24EX Flash Metering Problem


SteB wrote:
My experience has been the same. I did the same thing Dalantech describes - that is switching betwee E-TTL evaluative and average metering. In both cases the exposure pattern (including over-exposure) was the same. In my experience evaluative TTL flash not just on Canon, but on all the systems I have used or tried works in a similar way. There is a tendency to under-exposure in tricky lighting. Normally serious over-exposure is rare with evaluative metering as the intention appears to be to save the highlights.


Thankls SteB!



Sep 15, 2008 at 05:09 PM
michael kilner
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p.1 #15 · p.1 #15 · 40D and the MT-24EX Flash Metering Problem


out of curiosity John,does your MR-14 work ok with the 40d?


Sep 15, 2008 at 05:21 PM
Dalantech
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p.1 #16 · p.1 #16 · 40D and the MT-24EX Flash Metering Problem


michael kilner wrote:
out of curiosity John,does your MR-14 work ok with the 40d?


I haven't used it enough to tell -I've spent all year trying to get good light quality out of the MT-24EX. Picturing the light in my head I'd say no, that the MR-14EX wouldn't have the same problem since with it I'd be more likely to throw enough of the E-TTL pre-flash onto the subject and its surroundings to get a good exposure.

I'll put the MR-14EX in my bag and the next time I shoot here in town I'll take a couple of test shots to see how well it performs.



Sep 15, 2008 at 05:47 PM
Daemonoropsis
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p.1 #17 · p.1 #17 · 40D and the MT-24EX Flash Metering Problem


I tried writing to my local canon hq who wrote back telling me at the issue wasnt a known problem and they just suggested upgrading the firmware an sending it in to a shop to see if it was a repair covered under warrenty!

I can only encourage people to write to their local canon and telling them about the problem.

I hope we can raise enough awareness to make them act, but I fear its a lost cause



Sep 26, 2008 at 06:59 PM
Dalantech
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p.1 #18 · p.1 #18 · 40D and the MT-24EX Flash Metering Problem


Daemonoropsis wrote:
I hope we can raise enough awareness to make them act, but I fear its a lost cause


I'm hoping that someone at Canon sees my posts on all of this and does something about it...



Sep 26, 2008 at 07:49 PM
rich.10
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p.1 #19 · p.1 #19 · 40D and the MT-24EX Flash Metering Problem


I've noticed a similar thing with my 40D and MR14 EX, and also with my 550EX. When shooting a short burst, quite often I notice that the first shot is about 1/3 stop over exposed, with the following shots correct.

I haven't bothered to do any investigative tests, but I notice it quite regularly.

Rich.



Sep 26, 2008 at 10:20 PM
Dalantech
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p.1 #20 · p.1 #20 · 40D and the MT-24EX Flash Metering Problem


rich.10 wrote:
I've noticed a similar thing with my 40D and MR14 EX, and also with my 550EX. When shooting a short burst, quite often I notice that the first shot is about 1/3 stop over exposed, with the following shots correct.

I haven't bothered to do any investigative tests, but I notice it quite regularly.

Rich.


Thanks Rich! The problem is even more pronounced with the MT-24EX. What you're seeing is manageable, because 1/3 of a stop is easy to compensate for in post and the other images are good. I can take a six shot spread and maybe one of them will be dead on with the rest over exposed by varying amounts -but the good one often is a frame in the middle...



Sep 27, 2008 at 05:33 AM
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