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12-05-2007, 05:25 PM   #1
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540 FGZ + K10D flash exposure compensation

While doing some testing today, I think I solved a little mystery that's been bugging me for months.

It seems pretty clear that the K10D's own flash exposure compensation setting (in the Fn menu) has an ADDITIVE effect, when used in combination with the 540 FGZ. If you can't figure out why your shots are under- or over-exposed, hit the Fn button and check the flash setting in the camera: It may be set to -2 or +1. I say that this has an additive effect when you use the 540 because the camera's own setting is combined with the flash unit's setting to produce the flash output. For example, -1 in the camera's Fn menu and +1 on the back of the 540 = 0 in both places. And +1 in the camera and +1 on the back of the 540 = +2. I've never seen this mentioned anywhere. Seems to work in wireless mode, as well.

Maybe everybody knows it but me, but I was both surprised and happy when I figured this out.

Will

12-05-2007, 05:51 PM   #2
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that just seem retarded to me if there's no way to stop that.. There should be a way to completely control the unit from the camera - period!
12-05-2007, 06:57 PM   #3
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QuoteOriginally posted by Tom M Quote
that just seem retarded to me if there's no way to stop that.. There should be a way to completely control the unit from the camera - period!
Interesting reaction, Tom. I also thought it was very queer at first, but what I felt was that the flash should be controlled entirely from the 540's control panel, which after all is easier to get to than the Fn menu.

But now that I've gotten over my surprise, I've decided it's not a BAD thing after all. So long as you know how it works, you can make it work for you rather nicely. For example, say you're shooting wirelessly and the flash is on a flash stand 10 ft away, while you're at the camera which is mounted on a tripod. Rather than hike over to the 540 to dial up the flash, you can do it from the camera. And of course, if the camera's setting is at +/-0 FEC, then you can control the flash normally from the dial on the back of the 540. Finally, I have complained in the past that the 540 can't go to +2, and I will also confess that I was mostly voicing complaints I heard from others. Well, I think now that's not quite correct. If I dial the 540 to +1 and do the same thing in the camera, I get more flash output than I do otherwise. So apparently it is possible to get +2 FEC. You just have to do it by combining these adjustments.

For the most part, I think the key lesson here is, if you're not getting the exposure you expect while using a 540 FGZ, check the camera's flash exposure compensation setting in the Fn menu. That's what led me to this little personal discovery. I was doing some tests and kept getting darker exposures than I expected and it took me fifteen minutes of playing around before I noticed that the Fn menu's FEC was dialed down to -2.

What I don't understand is, how does this affect the output from TWO flashes? I've been testing wireless using the on-camera flash only as a trigger/controller. But when I go into the custom menu and change the setting for flash output in wireless mode to On (so the camera's built-in flash contributes its light to the picture), it seems to me that the result is STILL additive. This is a bit harder for me to test, at least I have a harder time figuring out how to detect the relative contribution of the two flashes. I've put the off-camera flash off to the side and throwing its light very clearly in a direction different from the on-camera flash, which is throwing its light straight forward. As far as I can tell, changes to the on-camera FEC affect the output from BOTH light sources. When I dial the Fn menu's FEC down to -2, not only does the light on the front of the subject get diminished, the light from the side (coming from the 540FGZ) is diminished, also. THIS makes my head hurt at the moment and I'm not going to bother getting the other 540 out and trying THREE flashes until I've had a chance to get a good night's rest.

Will

Will
12-05-2007, 07:13 PM   #4
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I ALWAYS use the 540 with FEC set to +1 on the flash unit. Pictures come out nicely exposed....Sometimes they are on the verge of overexposure, but since I shoot RAW, I can bring down the exposure in ACR if needed.

12-06-2007, 05:28 AM   #5
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QuoteOriginally posted by WMBP Quote
While doing some testing today, I think I solved a little mystery that's been bugging me for months.

It seems pretty clear that the K10D's own flash exposure compensation setting (in the Fn menu) has an ADDITIVE effect, when used in combination with the 540 FGZ. If you can't figure out why your shots are under- or over-exposed, hit the Fn button and check the flash setting in the camera: It may be set to -2 or +1. I say that this has an additive effect when you use the 540 because the camera's own setting is combined with the flash unit's setting to produce the flash output. For example, -1 in the camera's Fn menu and +1 on the back of the 540 = 0 in both places. And +1 in the camera and +1 on the back of the 540 = +2. I've never seen this mentioned anywhere. Seems to work in wireless mode, as well.

Maybe everybody knows it but me, but I was both surprised and happy when I figured this out.

Will
Judging from the PTTL problem threads on DPreview, no one realizes this interaction between camera and 540FGZ but you. Maybe you should post your findings there as well.
12-06-2007, 05:35 AM   #6
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Thanks, Will. Informative as always. I am intrigued by the possibility of getting +2 FEC by setting both the flash and camera to +1. I will have to experiment, too.
12-06-2007, 08:22 AM   #7
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for me, i alway have problem in pttl mode. exposure alway off. switch to manual mode on flash. the result is alot better and more consistent. my 2 cent
12-06-2007, 08:31 AM   #8
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QuoteOriginally posted by kingkongva Quote
for me, i alway have problem in pttl mode. exposure alway off. switch to manual mode on flash. the result is alot better and more consistent. my 2 cent
I too have problems with P-TTL, but they are uncommon. First thing I would suggest is, check your in-camera FEC settings.

12-06-2007, 08:59 AM   #9
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QuoteOriginally posted by baldeagle21b Quote
Judging from the PTTL problem threads on DPreview, no one realizes this interaction between camera and 540FGZ but you. Maybe you should post your findings there as well.
I have a feeling that it is not all together an unknown fact as I have seen some posts in DP eluding to this fact. I noticed it with my camera that they were additive, I never had to negatively compensate thus far, and it is good to know it goes both ways.


Magic lantern is wrong in this regard as it clearly say's it's one or the other and even says the settings on the flash takes precedence over the camera body.
12-06-2007, 03:14 PM   #10
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I actually recall a few (but not many, and not specifically regarding this topic) threads mentioning this already. FEC from the body and external flash stacks with one another, so one has a -5 to +2 EV using the pentax flash system.

The FEC stacking is also true for other camera manufacturers as well.

When using the external flash for a series of shots, I often set the body to +1 and the flash to -1. So combined I'm actually starting at 0 EV, but can get a -2 to +2 EV by changing the FEC only (faster than going tho the body to make the change).
12-06-2007, 03:31 PM   #11
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QuoteOriginally posted by AVANT Quote
I actually recall a few (but not many, and not specifically regarding this topic) threads mentioning this already. FEC from the body and external flash stacks with one another, so one has a -5 to +2 EV using the pentax flash system.

The FEC stacking is also true for other camera manufacturers as well.

Avant,

That's interesting to know.

I'm mainly glad to know that I can get more light from the 540 than I thought I could. But I remain a bit confused about how this works when I am using, say, two external flash units at once. I've only done this occasionally, and I didn't have time last night to play with it. It looks to me like the camera would somehow affect both of the external units.

I'm wondering now if this has something to do with the contrast-control sync option on the flash. I asked about that here some time ago and didn't understand the answers I got. My hypothesis is that contrast control might allow you to control the output of each unit independently, rather than getting this additive or stacked result. I'll try to test that tonight.

Will
12-06-2007, 04:00 PM   #12
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QuoteOriginally posted by WMBP Quote
I'm wondering now if this has something to do with the contrast-control sync option on the flash. I asked about that here some time ago and didn't understand the answers I got. My hypothesis is that contrast control might allow you to control the output of each unit independently, rather than getting this additive or stacked result. I'll try to test that tonight.

Will
The contrast control sync only has effect in the contrast control mode. Contrast control is really just a ratio of light setup like this... (Master Light Source) : (Slave Light Source).

For example, if you use one external unit that was set to operate wireless and 1:2 contrast ratio, it will mean your built-in flash becomes the master light source, and your external is now the slave light source. When you take a picture, your slave light source will be twice as bright as your master light source.

So how would FEC be related to contrast control? Your master light source uses it! So you would use FEC like you normally would in P-TTL mode, and your slave light source will always attempt to be twice as bright on the final exposure, etc.

I say "on the final exposure" because twice as bright isn't always twice the output power.

As with every other mode, there are goods and bads, but that should probably be a different discussion.


------------------------

Using contrast control sync mode is one of solving your previously mentioned problem earlier regarding FEC stacking even when the built-in flash is set to master. (FYI: It's suppose to always stack)

------------------------

Oh one other note, FEC set on the external flash unit doesn't show up in your exif :\ Only the camera body's FEC value.

Last edited by AVANT; 12-06-2007 at 04:06 PM.
12-06-2007, 05:26 PM   #13
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Got a flash meter?

The easiest way to find out is to set flash to +1 and camera to 0, take shot and use a flash meter to determine output. Then jump the camera setting up to +1 and take a shot.

Using the flash meter see if there is a recordable difference in output.

I don't a flash meter, but I am assuming someone here will and can do this quickly to confirm your assumptions.

Crash
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