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01-30-2016, 09:00 PM   #1
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Undocumented camera behavior using pop up flash.

I posted this in the photo comp but then realised there was a five sentence limit so I've reposted it here, has any one else come across this behavior or is this old news to forum members, still you shouldn't have to go to forums or 3rd party sources to learn how you camera works, it should be in the manual .


BEWARE - Undocumented camera behavior using pop up flash.


This problem applies to my K30 & K20D and has also been tested on K200 so I'm assuming other models behave in a similar manor.
Here's the problem, so if you put the camera into manual mode you expect it to be fully controllable by the manual settings you select... right! Well no, not if you use the on board flash in conjunction with an "A" lens. This is easily checked by taking a series of shots at different aperture setting (using the camera to control aperture), If you select setting that will overexpose the shot the camera will automatically shut the exposure off when it thinks it has enough light, all the exposures will be similar (until there's not enough light). How is the Camera doing this? its in manual mode, the exposures should range from overexposed to under exposed! It will be overexposed if its a non "a" lens or if the lens has an aperture ring and you take it off the "A" setting. The only way I can see the camera being able to do this is to electronically cut the exposure time short once its determined it has enough light. - none of this is documented in the owners manual!

So this is what happened to me - doing a photo shoot for a dance school, (costume night), a backdrop, 2 x optically triggered strobes pointing into reflective umbrellas in basic clam shell arrangement, I used the same arrangement last year with good results, the setting were such that the pop up flash was not contributing much at all to lighting of the scene, but triggering the strobes, I was using a Tokina 28-70 f2.8 ATX pro, (an "A" type lens). last year I physically set the aperture using the ring on the lens, all went well. This year I decided to use the camera to control the aperture (there were reasons for this). A couple of quick test shots to check exposure and off we went, 150 shots later during a lull in proceedings I zoom in on a couple of shots, eek! a horrible shadow on all the left hand edges or under edges depending on orientation, caused by on board flash, Devastation. It took me several days & some testing to figure what had happened. My setting were such that the camera was shutting off the exposure before the optical strobes triggered, ie. even though the strobes flashed the exposure was already shut off due to the action described above, the result was that I'd taken 150+ shots effectively using only the onboard flash complete with the horrible shadows and ordinary flat lighting.
It took many, many hours of post processing to remove the shadows (do the math). Ok, my bad for not having a detailed look at the test shots but when your under pressure... but really when you put the camera into manual mode you do expect it to be in manual .... so BEWARE.. The owners manual regarding flash operation is shameful.


Last edited by Cee Cee; 01-31-2016 at 07:07 AM.
01-30-2016, 09:05 PM   #2
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Can you post some files with exif intact?
01-30-2016, 09:10 PM   #3
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I might be wrong, I am not all that knowledgeable about optically triggered flash. However, when I tried doing that the on board pre-flash would trigger the strobes, thus setting them off prior to the camera making the exposure. So they did go off but did not contribute to the exposure. I'm assuming your "optically triggered strobes" are just full manual strobes, not P-TTL? I think the k-3 has a fully manual setting for it's on board flash but AFAIK it is the first Pentax to have that. Sorry if I've misunderstood, just trying to understand the issue.
01-30-2016, 09:57 PM   #4
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QuoteOriginally posted by UncleVanya Quote
Can you post some files with exif intact?
I don't really have permission from the dance school. Basic settings F5.6 1/125sec 0EV ISO 280


QuoteOriginally posted by jatrax Quote
I might be wrong, I am not all that knowledgeable about optically triggered flash. However, when I tried doing that the on board pre-flash would trigger the strobes, thus setting them off prior to the camera making the exposure. So they did go off but did not contribute to the exposure. I'm assuming your "optically triggered strobes" are just full manual strobes, not P-TTL? I think the k-3 has a fully manual setting for it's on board flash but AFAIK it is the first Pentax to have that. Sorry if I've misunderstood, just trying to understand the issue.
my tests confirmed the stobes were late to fire, the on board flash must wait for the shutter to open before it fires so I don't see how the strobes could be optically triggered before the shutter opened. The thing is by there very nature there must be a short delay for the stobes to trigger. The problem is the camera shutting off the exposure electronically before the 1/125 sec exposure time, and the optical strobes not responding in time - its this undocumented behavior of the camera which is the problem. Now that I know about it the situation can be avoided. You should put it to the test with a series of shots using the onboard flash with an "A" lens across the range of availble apertures using the camera to control the aperture with the lens ring in the "A" position, in manual mode. Then repeat the sequence using the aperture ring on the lens to set the aperture, the first set will be reatively constant exposure until there's not enough light when the shots will darken. The second set will show relative expoure variation from totally blown out to dark as you would expect.


Last edited by Cee Cee; 01-30-2016 at 10:03 PM.
01-30-2016, 10:16 PM   #5
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I doubt that the set 1/125s exposure time was cut short. There is nothing to trigger such a behavior since the camera doesn't measure the exposure in real time after the shutter has opened.

The P-TTL pre-flash fires before the shutter opens as jatrax says and this will trigger the optically controlled flashes. If the aperture is off the A setting as you had it last year, P-TTL is disabled and there is no pre-flash to fire the strobes prematurely.
01-30-2016, 10:21 PM   #6
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QuoteOriginally posted by Cee Cee Quote
You should put it to the test with a series of shots using the onboard flash with an "A" lens across the range of availble apertures using the camera to control the aperture with then lens ring in the "A" position, in manual mode. The repeat the sequence using the aperture ring on the lens to set the aperture, the first set will be reatively constant exposure until there's not enough light when the shots will darken. The second set will show relative expoure variation from totally blown out to dark as you would expect.
I just tried this with my own K-30, with my built-in flash in wireless controller mode (contributes nothing to the exposure). The flash being controlled is a Pentax AF-540FGZ, set to manual mode, parked at a constant power level, in slave mode SL1 (wait for the P-TTL preflash).

When I set the lens to "A" and took a series of shots at f/1.7, f/4, f/8, and f/16, everything was as expected. Since the slave's output was constant, the shots progressed from overexposed to underexposed.

But when I set the aperture directly on the lens instead, the slave stopped firing completely, and the built-in flash took over. As it says on page 243 of the K-30 manual, "[Wireless flash mode] is not available [...] when the lens aperture ring is set to a position other than A."

That is, until I switched the AF-540FGZ to slave mode SL2 (don't wait for the P-TTL preflash). Then it fired in sync with the built-in flash, which was still firing for all its worth.

So I really think that what you're seeing is the difference between the built-in flash firing a preflash (lens in "A" mode) and not (lens not). It sounds like your off-camera strobes are set up to fire on any flash, and because of that, they're being triggered by the preflash from the built-in unit, and therefore firing too early to contribute to the exposure. Whereas, when you were shooting with the lens not in "A" mode, there was no preflash, so the strobes fired right along with the built-in flash.
01-30-2016, 10:49 PM   #7
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QuoteOriginally posted by Scintilla Quote
So I really think that what you're seeing is the difference between the built-in flash firing a preflash (lens in "A" mode) and not (lens not). It sounds like your off-camera strobes are set up to fire on any flash, and because of that, they're being triggered by the preflash from the built-in unit, and therefore firing too early to contribute to the exposure. Whereas, when you were shooting with the lens not in "A" mode, there was no preflash, so the strobes fired right along with the built-in flash.
^^^ This. What I tried to say above, but written better. When in 'A' mode your on board flash fires a PRE-FLASH to test the exposure. And that sets off the strobes before the camera takes the shot.
01-31-2016, 12:18 AM   #8
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QuoteOriginally posted by Ole Quote
I doubt that the set 1/125s exposure time was cut short. There is nothing to trigger such a behavior since the camera doesn't measure the exposure in real time after the shutter has opened.



The P-TTL pre-flash fires before the shutter opens as jatrax says and this will trigger the optically controlled flashes. If the aperture is off the A setting as you had it last year, P-TTL is disabled and there is no pre-flash to fire the strobes prematurely.
one would think so, but I beg to differ, the proof is in the pudding, do the test as I say, what else can be controlling the camera, is in manual mode, controlling the exposute time is all it can do to correct the exposure , the ISO is fixed, the shutter speed is fixed, the aperture is fixed. Of course the camera can electronically control the exposure, this is how all non SLR cameras work. Does any one really think the mechanical shutter can oprn & close in 1/5000 th of a sec.
this is nothing to do with pre flash ot P-TTL. To the eye the pop up flash and optical stobes all flash at the same time. So if the exposure time was 1/125 of a sec it would capture both, but it doesn't.

---------- Post added 01-31-16 at 06:19 PM ----------

QuoteOriginally posted by jatrax Quote
^^^ This. What I tried to say above, but written better. When in 'A' mode your on board flash fires a PRE-FLASH to test the exposure. And that sets off the strobes before the camera takes the shot.
no - no preflash

01-31-2016, 12:24 AM   #9
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QuoteOriginally posted by Cee Cee Quote
what else can be controlling the camera, is in manual mode
??

The camera is in manual mode, the flash is in P-TTL mode.

The K-30 has no manual control of its popup flash.

Listen to what these good people are trying to tell you! ☺

Tell your strobes to ignore the first flash if they have that function, or get yourself some cheap Cactus radio triggers.
01-31-2016, 12:44 AM   #10
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QuoteOriginally posted by jatrax Quote
^^^ This. What I tried to say above, but written better. When in 'A' mode your on board flash fires a PRE-FLASH to test the exposure. And that sets off the strobes before the camera takes the shot.
QuoteOriginally posted by Scintilla Quote
I just tried this with my own K-30, with my built-in flash in wireless controller mode (contributes nothing to the exposure). The flash being controlled is a Pentax AF-540FGZ, set to manual mode, parked at a constant power level, in slave mode SL1 (wait for the P-TTL preflash).

When I set the lens to "A" and took a series of shots at f/1.7, f/4, f/8, and f/16, everything was as expected. Since the slave's output was constant, the shots progressed from overexposed to underexposed.

But when I set the aperture directly on the lens instead, the slave stopped firing completely, and the built-in flash took over. As it says on page 243 of the K-30 manual, "[Wireless flash mode] is not available [...] when the lens aperture ring is set to a position other than A."

That is, until I switched the AF-540FGZ to slave mode SL2 (don't wait for the P-TTL preflash). Then it fired in sync with the built-in flash, which was still firing for all its worth.

So I really think that what you're seeing is the difference between the built-in flash firing a preflash (lens in "A" mode) and not (lens not). It sounds like your off-camera strobes are set up to fire on any flash, and because of that, they're being triggered by the preflash from the built-in unit, and therefore firing too early to contribute to the exposure. Whereas, when you were shooting with the lens not in "A" mode, there was no preflash, so the strobes fired right along with the built-in flash.
you are mis reading what I said - not external flash, if I use an external flash there is no problem this olnly occurs using popup flash with camera in "M" manual mode and a "A" type lens fitted.

Let me outline the test again

>use a "A" type lens, preferably with a aperature ring

> set the camera to M mode

>pop up the on board flash

>use settings, say ISO200 and 1/125sec 0EV

>make sure the aperature ring is set to "A" position

> take a series of shots changing the apertue using the camera to set the aperature say from f2.8 / f4 / f5.6 / f8 etc.

>now, you would expect to see a large variation in exposures, but I don't, the exposures are all reasonably constant !!!

>now take the same series of exposures, using the same apertures, only this time take the lens off the "A" setting and set the aperture using ring

>now what you see is great variation in exposures as you would expect

conclusion some how the camera is automatically controlling the exposure when an A type lens is fitted - even though the camera is in Manual mode.
The only way I can think that this can occur is to shorten the exposure time electronically as is done with mirrorless cameras.

---------- Post added 01-31-16 at 06:53 PM ----------

QuoteOriginally posted by clackers Quote
??

The camera is in manual mode, the flash is in P-TTL mode.

The K-30 has no manual control of its popup flash.

Listen to what these good people are trying to tell you! ☺

Tell your strobes to ignore the first flash if they have that function, or get yourself some cheap Cactus radio triggers.
sorry these good people are not understanding what I am saying

"The K-30 has no manual control of its popup flash" exactly my point yet somehow if you use the popup flash with an "A" lens in manual mode it does control the exposure. this doesn't need the strobes at all to prove this, do the test as I explain and then explain to me why the exposures are realtively constant when they shouldn't be

Last edited by Cee Cee; 01-31-2016 at 12:54 AM.
01-31-2016, 01:05 AM   #11
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The camera changes the flash duration to compensate for aperture changes. Even when using manual settings for shutter speed and aperture the camera tries to adjust exposure with the flash duration.
01-31-2016, 01:43 AM   #12
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QuoteOriginally posted by pentaxus Quote
The camera changes the flash duration to compensate for aperture changes. Even when using manual settings for shutter speed and aperture the camera tries to adjust exposure with the flash duration.
one of my initial thoughts, but this doesn't explain why the stobes are outside the exposure window of 1/125 , yet they are in the window if you set same lens apeture by the ring and use the same 1/125 hutter speed.
01-31-2016, 02:05 AM   #13
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That part of it is because if not in the A position the on board flash is always firing at full power.

http://support.us.ricoh-imaging.com/node/936
01-31-2016, 02:33 AM   #14
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QuoteOriginally posted by clackers Quote
That part of it is because if not in the A position the on board flash is always firing at full power.

K-x P-TTL "Pre-flash" | Ricoh Imaging Support
this is not applicable - I'm not using an auto mode!

but the camera is in manual mode - full manual control ! why don't I have full maunual control if I have an A lens fitted - and if I don't, it should be documented in the manual

but once again this doesn't explain the stobes being ouside the 1/125s window , yet inside the window if using non A lens or setting.

the test as I outline takes about 2 minutes - is anyone willing to do it
01-31-2016, 02:57 AM   #15
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QuoteOriginally posted by Cee Cee Quote
this is not applicable - I'm not using an auto mode!
The flash is in auto mode while the lens aperture is set to A.

QuoteOriginally posted by Cee Cee Quote
but the camera is in manual mode - full manual control ! why don't I have full maunual control if I have an A lens fitted - and if I don't, it should be documented in the manual
But you do. If you set it to f4 with the camera dial or the lens ring, it's f4.

QuoteOriginally posted by Cee Cee Quote
but once again this doesn't explain the stobes being ouside the 1/125s window , yet inside the window if using non A lens or setting.
I will try one last time, Cee Cee and then give up ... use the A setting, the P-TTL preflash sets the strobes off early. You say there is no pre-flash but you are wrong.

Don't use the A setting, there's no pre-flash, it fires once at full power and sets off the strobes at the same time.
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