Pre-flash on a Pentax... Silly Question?

CrazyJay

CrazyJay

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After a couple of days I have stumbled upon a flash problem, and not sure if I can bypass it or not?

when the flash is used, it fires a pre-flash first - presumably as red-eye reduction and or as a focus aid.

the problem is, I tried to photograph one of our sales managers, and he blinked on every single shot because of the pre-flash - (I resorted to taking ht esnap on my old compact instead, and the shot was fine.)

I can see this pre-flash will also rule out the use of a slave unit.

Anybody know if I can turn off the pre-flash please? - The model is Pentax K100D.

Thanks.

Also seems this camera might be a little heavier on batteries than I had anticipated
 
On my 350d you can hold the * button down,I think it is the exposure lock button, the pre flash will fire when you press the button, but not again when you take the shot. Then I can use a slave cell. I would think there was something similar you could do on your camera.

Chris.
 
Do you have the flash on red-eye reduction?

If it is like my GX-10 you need to press function, then select the flash mode, making sure its on standard.
 
The preflash is probably for flash metering and not focus/red eye.

If this is the case it is vital for correct flash exposure and cannot be disabled.
 
RichardtheSane said:
The preflash is probably for flash metering and not focus/red eye.

If this is the case it is vital for correct flash exposure and cannot be disabled.
Click to expand...

However, if you are in a manual mode, then exposure compensation shouldn't be required should it?

--
During some shows recently, my 400d was using multiple pre-flashes in order to do focus assist, (which I knew it didn't need, and didn't want to blind the performers), so I just held my left hand in front of it.
However, the focus assist on the 400d goes like:

flash flash flash, pause, FLASH

so I had time to remove it.
 
I am not referring to any form of exposure compensation. I'm referring to how the base output of the flash is determined by the camera.

On Canon the preflash always occurs and at the same level. The light reflected back from the preflash is then used to determine the required output of the main flash in order to expose the scene correctly. It cannot be disabled with ETTL flash.

I know on the 40D you can turn off the AF assist flashed from the onboard flash using a custom function, but you would still get the preflash.

CrazyJay, I don't know your camera specifics but have a check to see if there is a chapter in the manual referring to flash operation which covers this.
 
Thanks everybody. There's some good advise as usual
I didn't get a manual with the camera, so I might have to try to download one.

I'm sure I'll work a way round this somehow. :thinking:
 
CrazyJay said:
After a couple of days I have stumbled upon a flash problem, and not sure if I can bypass it or not?

when the flash is used, it fires a pre-flash first - presumably as red-eye reduction and or as a focus aid.

the problem is, I tried to photograph one of our sales managers, and he blinked on every single shot because of the pre-flash - (I resorted to taking ht esnap on my old compact instead, and the shot was fine.)

I can see this pre-flash will also rule out the use of a slave unit.

Anybody know if I can turn off the pre-flash please? - The model is Pentax K100D.

On the basis that it works the same in your camera as in my Pentax it is for red eye reduction in people or animals (green eye in my dog).
The theory is that a burst of light is fired to to cause the subject to reduce pupil size in it's eyes and so minimise reflection.
You should be able to turn it off in the menu.

Thanks.

Also seems this camera might be a little heavier on batteries than I had anticipated
Click to expand...
 
OK, this one has had me thinking so I did some digging.

The preflash does appear to be the metering part of P-TTL flash so cannot be disabled in any menu.

However coldpenguin was onto something when referring to manual. If you put the camera into A or M mode then by all accounts the preflash will not fire. You may, however, have to adjust the aperture manually to control the flash exposure. (The manual is unclear on this)

http://www.pentaximaging.com/files/manual/K100D Manual.pdf

Have a read of the flash section from P154 onwards

HTH
 
There's a separate red-eye reduction pre-flash but it's correct that the P-TTL flash metering uses its own pre-flash. I cannot perceive it, apart from through the viewfinder, just before it blacks out when the mirror flips up.

Current Pentax external flashes have an LED spotbeam focus aid; the pop-up flash will strobe in dark conditions for the same purpose.

The pre-flash doesn't occur with the external flash in A or M mode (I rarely use the pop-up, but checking just now it seems to pre-flash all the time). The spotbeam doesn't work in the flash's A mode, but does in M (go figure!).

I mis-read CrazyJay as having a K10D so the following may not be relevant: http://www.pentaxforums.com/forums/pentax-dslr-discussion/34478-k10d-pre-flash-how-stop.html
 
CrazyJay said:
After a couple of days I have stumbled upon a flash problem, and not sure if I can bypass it or not?

when the flash is used, it fires a pre-flash first - presumably as red-eye reduction and or as a focus aid.
the problem is, I tried to photograph one of our sales managers, and he blinked on every single shot because of the pre-flash - (I resorted to taking ht esnap on my old compact instead, and the shot was fine.)

I can see this pre-flash will also rule out the use of a slave unit.

Anybody know if I can turn off the pre-flash please? - The model is Pentax K100D.

Thanks.

Also seems this camera might be a little heavier on batteries than I had anticipated
Click to expand...

My guess is that you have somehow set the camera for second-curtain flash sync, with a slowish shutter speed. Switch it back to first-curtain (normal) sync and the problem is solved.

Second curtain sync separates the two flashes, which are normally so close together they appear as one, and the only person that knows there actually was a prefash is the photographer, as you can see it through the viewfinder before the mirror blackout and the main flash fires.

I think all modern flash system work in the same way - pre-flash is for flash metering only, does nothing else - but there may be different operational details. For example, with Canon with manual mode there is no pre-flash, and using Flash Exposure Lock (FEL) disables it too, as it's unnecessary. The long stream of flashes mentioned in another thread sounds like a Modelling Flash, triggered by the lens-stop-down button on Canons :thinking:
 
coldpenguin said:
However, if you are in a manual mode, then exposure compensation shouldn't be required should it?

--
During some shows recently, my 400d was using multiple pre-flashes in order to do focus assist, (which I knew it didn't need, and didn't want to blind the performers), so I just held my left hand in front of it.
However, the focus assist on the 400d goes like:

flash flash flash, pause, FLASH

so I had time to remove it.
Click to expand...
i have the 10d and 5d. But I know nothing about 400d. Are you saying the 400d fires 4 flash`s. I have a gadget to overcome the preflash prob, but not 3 preflash`s.
 
HoppyUK said:
Switch it back to first-curtain (normal) sync and the problem is solved.
Click to expand...

Unfortunately not.

The slow shutter speed with trailing curtain sync certainly lengthens the time between flashes (as does the timer delay / mirror lockup) and, if anything, would improve the shots of subjects who blink due to the pre-flash, if they have time to complete their blink.

The OP is most probably referring to use of the pop-up flash, which doesn't have trailing curtain sync capability, but he should try the timer delay trick (camera held steady on a tripod or bean bag etc).

To answer another point, the Pentax optical slave system built into the current flashes works fine with the pop-up flash.
 
classcams said:
i have the 10d and 5d. But I know nothing about 400d. Are you saying the 400d fires 4 flash`s. I have a gadget to overcome the preflash prob, but not 3 preflash`s.
Click to expand...

It's the low light AF assist on the 400D It strobes a bit to help with autofocus.

On the 400D you can turn that off using Customer Function 5 (Set to 2 so external can still emit)
 
classcams said:
i have the 10d and 5d. But I know nothing about 400d. Are you saying the 400d fires 4 flash`s. I have a gadget to overcome the preflash prob, but not 3 preflash`s.
Click to expand...

It is the AF pre-flash /strobe, not the metering flash that I was refering to unfortuantely.
I have also remembered since, that I left my camera on second curtain sync (which is available with the onboard 400d flash as well BTW), which means that I had a little extra time for removing the hand.

Not too sure I understand why the camera would have to pre-flash meter when you are in full-manula mode.
 
Camera on manual, pre-flash will still fire as flash attempts to match f/number set.

Switch flash to manual also, should cancel the pre-flash.
 
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