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06-26-2011, 04:42 PM   #1
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PTTL flash with bounce card

I'm getting consistently under-exposed shots using a bounce card attached to my p-TTL flash, thus I wonder if it has more to do than exposure compensation on my camera ?

Does anybody have experience getting good results from bounce cards in p-TTL mode? would appreciate some tips on indoor and outdoor fill-flash setups.

I want to avoid going to manual mode because that defeats the purpose of buying a pentax dedicated pttl flash system. Thanks in advance!

06-26-2011, 06:17 PM   #2
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Which camera model are you using? I get under exposure with the K10D & K20D.
06-26-2011, 09:08 PM   #3
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No problem with my K7 and 540. Here's my test setup: K7 + DA* 16-50mm + 540 + Metz bounce card:



Here's a test photo (ISO 200, F/5.6, 1/60 sec, Av mode, p-TTL flash mode, 26mm FL, spot metering, no exposure compensation):

06-27-2011, 07:38 AM   #4
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Thanks, exposure looks good! It looks like what I get after +2EC

Couple of questions:

1. Are you spot metering off the white wall ?

2. How far away is the wall from camera/flash position?


QuoteOriginally posted by SOldBear Quote
No problem with my K7 and 540. Here's my test setup: K7 + DA* 16-50mm + 540 + Metz bounce card:



Here's a test photo (ISO 200, F/5.6, 1/60 sec, Av mode, p-TTL flash mode, 26mm FL, spot metering, no exposure compensation):


06-27-2011, 11:07 AM   #5
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QuoteOriginally posted by jackseh Quote
1. Are you spot metering off the white wall ?
Yes and no

No because I pre-focused at the violin using the center focus sensor, happening to be in the same location of the center focus sensor. I then recomposed and shot. I did this out of habit.

Yes because p-TTL flash metering is done during the pre-flash strobe, which happened after I've recomposed the photo. At that time, the metering spot happened to be on the white wall.

I don't think the metering mode matters. I also did the test with matrix metering. The result is the same: good consistent exposure.

QuoteOriginally posted by jackseh Quote
2. How far away is the wall from camera/flash position?
About 10 ft.

There is a thread on dpreview Pentax DSLR forum on similar topic: link. My posts (with test result) are around the middle of the thread. In this case, I bounced the flash off the ceiling. But the equipment doesn't know the difference between the ceiling and the bounce card.
06-27-2011, 06:52 PM   #6
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Thanks, very informative thread!

I think I read somewhere on this forum which said p-TTL is caliberated to 18% grey? So for instance, if the spot metering is off a white wall, exposure compensation must be applied to achieve proper spot exposure for it ?



QuoteOriginally posted by SOldBear Quote
Yes and no

No because I pre-focused at the violin using the center focus sensor, happening to be in the same location of the center focus sensor. I then recomposed and shot. I did this out of habit.

Yes because p-TTL flash metering is done during the pre-flash strobe, which happened after I've recomposed the photo. At that time, the metering spot happened to be on the white wall.

I don't think the metering mode matters. I also did the test with matrix metering. The result is the same: good consistent exposure.



About 10 ft.

There is a thread on dpreview Pentax DSLR forum on similar topic: link. My posts (with test result) are around the middle of the thread. In this case, I bounced the flash off the ceiling. But the equipment doesn't know the difference between the ceiling and the bounce card.
06-27-2011, 09:21 PM   #7
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QuoteOriginally posted by jackseh Quote
I think I read somewhere on this forum which said p-TTL is caliberated to 18% grey? So for instance, if the spot metering is off a white wall, exposure compensation must be applied to achieve proper spot exposure for it ?
You're correct that if the spot metering was off the white wall, the test photo would be darker because the sensor assumed 18% grey.

But I don't think it's spot metering, even though the switch is set at spot metering. I think it's still matrix metering.

When I composed the photo so that the computer monitor (black) was at the center, I still got the same exposure as when the white wall was at the center.
06-27-2011, 09:28 PM   #8
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Who is the maker of the guitar?

06-27-2011, 10:37 PM   #9
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QuoteOriginally posted by Pepe Guitarra Quote
Who is the maker of the guitar?
It's a mid-range Yamaha classical. I'm not guitarist by any stretch of imagination. In fact, I haven't touched it since I got carpal tunnel syndrome about 2 years ago.
06-28-2011, 03:06 AM   #10
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Make sure you do your tests on something without specular highlights.
PTTL will notoriously underexpose to keep highlights from blowing out, even specular tiny highlights.
PTTL pretty much sucks in this regard but seems to have improved a lot in the K5.

Also keep in mind that flash metering uses the full sensor. Spot metering for example, will have no effect on how the flash responds to the environment.
06-28-2011, 08:28 AM   #11
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Thanks all!

I have another question regarding Contrast Control Sync mode, hoping to get some answers.

The manual says in this mode the two flashes are fired separately (metered separately). Thus can I bounce the stronger flash without any underexposure issues, assuming it will be metered to match the fill ratio ?

How does the camera meter two flashes separately? is it firing the first one in front curtain while the other in rear curtain?
06-28-2011, 01:02 PM   #12
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Metering flash occurs before exposure. Some people's eyes are sensitive enough to catch both flashes. Thus why you'll get half closed eyes in some flash photos when PTTL and similar tech is used. Watch for it, and you may see it. Turn on 2 second timer delay and you'll definitely see what is happening.

But basically in contrast mode, one flash will fire at half the power of the other. This ratio is always constant.
I do not believe the camera meters off both (i.e. does not take two meter readings), but will take a meter reading off some pre-flash and calculate the necessary range to split amongst the two flashes.
06-28-2011, 04:13 PM   #13
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QuoteOriginally posted by amoringello Quote
Metering flash occurs before exposure. Some people's eyes are sensitive enough to catch both flashes. Thus why you'll get half closed eyes in some flash photos when PTTL and similar tech is used. Watch for it, and you may see it. Turn on 2 second timer delay and you'll definitely see what is happening.

But basically in contrast mode, one flash will fire at half the power of the other. This ratio is always constant.
I do not believe the camera meters off both (i.e. does not take two meter readings), but will take a meter reading off some pre-flash and calculate the necessary range to split amongst the two flashes.
I must have read it off an old flash manual, because I'm trying it on film bodies which has TTL (not PTTL). In TTL mode it is limited to 1/60 because the manual says two flashes are fired separately so the camera can meter them separately in TTL. So I'm wondering if this is done in front & rear curtain , because in TTL there is no preflash, correct?

However, in PTTL mode the meter takes one reading and calculate the split ?
06-28-2011, 04:19 PM   #14
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QuoteOriginally posted by jackseh Quote
In TTL mode it is limited to 1/60 because the manual says two flashes are fired separately so the camera can meter them separately in TTL.
I think my SuperA has sync speed of 1/125 sec.

QuoteOriginally posted by jackseh Quote
However, in PTTL mode the meter takes one reading and calculate the split ?
I think so.

I haven't done any test to verify my theory, but I don't think p-TTL is smart enough to measure light from each remote flash individually. Rather, it calculates the total light needed, then divides the light from each remote flash. When doing so it assumes the same distance from the object being photographed to each individual remote flash.

I may do some testing tonight if I have a chance.

Last edited by SOldBear; 06-28-2011 at 04:45 PM.
06-28-2011, 04:33 PM   #15
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QuoteOriginally posted by SOldBear Quote
I think my SuperA has sync speed of 1/125 sec.
I don't have a SuperA but I think it is not listed as a model that support Contrast Control Sync.

According to the manual, on TTL cameras that support Contrast Control Sync, only AFXXX FTZ flashes can be used for this mode, not the new FGZ models which only does it in PTTL.

bdimitrov site has some info on TTL in contrast control mode, that's where I got my info regarding sync speed.

Not sure if it would work using one flash as bounce. Ideally, TTL will expose it according to the fill ratio because TTL measure two flashes separately.
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