K20 P-TTL question

K-9 · 07-26-2009, 05:45 PM

I've never tried an external P-TTL flash but was reading through the manual and it says you set the flash mode to Auto P-TTL and this makes a "pre-flash" fire right before the actual flash? I was wondering if this is like double the flash for every shot you take and is there a slight shutter delay for it to take the exposure? Thanks

Matjazz · 07-27-2009, 05:43 AM

Your built-in flash works in the same manner. The pref lash is usually several stops weaker than exposure flash. So yes it fires twice but it doesn't use even near as much as twice the power. As for the delay, I guess there is some, but I haven't been able to notice it so far.

WalterGA · 07-27-2009, 12:43 PM

Is that different from the double-flash you get using red-eye reduction?

**Ash** · 07-28-2009, 02:58 AM

Yes, completely separate. Red-eye will activate a separate pupil-constricting flash to limit the red-eye effect.

**Rondec** · 07-28-2009, 05:07 AM

You won't actually see the preflash. It is lower power and very brief. It is nothing like the red eye reduction flashes (which are really annoying).

**Ash** · 07-28-2009, 05:20 AM

Although if you look carefully, you'll notice the pre-flash go off in the viewfinder immediately before the mirror flips up to take the exposure.

WalterGA · 07-28-2009, 07:51 AM

What's the point of the pre-flash?

egordon99 · 07-28-2009, 07:58 AM

Originally posted by WalterGA

What's the point of the pre-flash?

So the camera's exposure meter can determine what power the main flash needs to fire at during the exposure.

You CAN see the pre-flash if you use rear-curtain sync and a slow-ish shutter speed (~1 second or slower) You'll see the pre-flash, shutter opens, right before the shutter closes you'll see the main flash.

WalterGA · 07-28-2009, 04:33 PM

Thanks for the info. Couple hours ago, I did what I should have initially done...read about PTLL in my K20 manual!

07-26-2009, 05:45 PM	#1
K-9 Veteran Member Join Date: May 2009 Location: USA Photos: Albums Posts: 1,971	K20 P-TTL question I've never tried an external P-TTL flash but was reading through the manual and it says you set the flash mode to Auto P-TTL and this makes a "pre-flash" fire right before the actual flash? I was wondering if this is like double the flash for every shot you take and is there a slight shutter delay for it to take the exposure? Thanks

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07-27-2009, 05:43 AM	#2
Matjazz Veteran Member Join Date: Sep 2006 Location: EU/Slovenia Photos: Gallery Posts: 774	Your built-in flash works in the same manner. The pref lash is usually several stops weaker than exposure flash. So yes it fires twice but it doesn't use even near as much as twice the power. As for the delay, I guess there is some, but I haven't been able to notice it so far.

07-27-2009, 12:43 PM	#3
WalterGA Senior Member Join Date: May 2009 Location: Atlanta Posts: 110	Is that different from the double-flash you get using red-eye reduction?

07-28-2009, 02:58 AM	#4
Ash Loyal Site Supporter Join Date: Mar 2007 Location: Toowoomba, Queensland Photos: Gallery \| Albums Posts: 23,920	Yes, completely separate. Red-eye will activate a separate pupil-constricting flash to limit the red-eye effect.

07-28-2009, 05:07 AM	#5
Rondec Loyal Site Supporter Join Date: Mar 2009 Location: Gladys, Virginia Photos: Gallery Posts: 27,663	You won't actually see the preflash. It is lower power and very brief. It is nothing like the red eye reduction flashes (which are really annoying).

07-28-2009, 05:20 AM	#6
Ash Loyal Site Supporter Join Date: Mar 2007 Location: Toowoomba, Queensland Photos: Gallery \| Albums Posts: 23,920	Although if you look carefully, you'll notice the pre-flash go off in the viewfinder immediately before the mirror flips up to take the exposure.

07-28-2009, 07:51 AM	#7
WalterGA Senior Member Join Date: May 2009 Location: Atlanta Posts: 110	What's the point of the pre-flash?

07-28-2009, 07:58 AM	#8
egordon99 Inactive Account Join Date: Dec 2006 Location: Outside of Philly Posts: 1,561	Originally posted by WalterGA What's the point of the pre-flash? So the camera's exposure meter can determine what power the main flash needs to fire at during the exposure. You CAN see the pre-flash if you use rear-curtain sync and a slow-ish shutter speed (~1 second or slower) You'll see the pre-flash, shutter opens, right before the shutter closes you'll see the main flash.

07-28-2009, 04:33 PM	#9
WalterGA Senior Member Join Date: May 2009 Location: Atlanta Posts: 110	Thanks for the info. Couple hours ago, I did what I should have initially done...read about PTLL in my K20 manual!