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01-11-2013, 12:38 PM   #1
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Flash Compensation, Overall Compensation and Ambient Lights

I recently got into flash photography so I've been digging around a lot for information and learn as much as I can. I understand the 2 light source of ambient light and flash light and how both contribute to your single photo. I've also tried to read through the manuals of both the flash gun ad the K5 camera. Its a bit challenging since you have to read two manuals and combine the procedures into one. I have a question which may have been answered already but I haven't been able to find it on the forums or through googling. So please be patient and help point me toward the answer if I've missed it. This may sound like a total newbie question and my understanding here could be a bit flawed.

I'm trying to understand the difference between Overall Compensation and Flash Compensation as it relates to K5 camera. The K-5 body has has the overall compensation +/- Button and also a Flash compensation in the menu. The external flash has a flash compensation setting as well. From what I've read so far The Flash compensation from the camera (the one in th menu? not the +/- button?) and the flash unit does the same thing and its additive. Now how does the overall +/- overall compensation button on the camera body effect the flash compensation? Does it control the exposure for the ambient light or the overall exposure? I guess I'm trying to find out the relationship between the +/- compensation button, the flash compensation found in onscreen menu and the flash compensation found on the flash.

I found this site which mentions how they behave in Nikon and Canon but can anyone explain their relation in the K-5 or pentax? http://neilvn.com/tangents/flash-photography-techniques/8-flash-exposure-comp/

Sorry about the convulated and confusing question.

01-11-2013, 02:30 PM   #2
HSV
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The p-ttl system is very confusing (compared to the Nikon CLS system), so far, I have concluded the following:

1. the built in flash is controlled by the flash compensation of the body
2. the external flash is not controlled by the flash compensation of the body, but it controlled by the compensation in the flash unit

3. when the body is in manual or X mode, the exposure compensation of the body can control the power of the external flash
4. as far as I know, in the automatic or semi automatic modes, the external flash can only be controlled by the compensation in the flash

I don't know how exactly the flash metering works in p-ttl, but according to my tests (using an adjacent black and white carton), it's definitely not spot...it can be "matrix" or overall.
01-11-2013, 02:50 PM   #3
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Original Poster
Yeah I've been taking a lot of test shots all day today trying to figure out the effects of the different settings. Right now I can't seem to get the p-ttl to expose properly without flash compensation of -1 or more (bounce off the ceiling or wall). The Auto mode of the flash is exposing perfectly but the p-ttl is constantly overexposing without flash compensation dialed in so just trying to figure out the differences between the compensation settings. Its a bit confusing since I thought p-ttl was suppose to be more accurate than the Auto mode. Manual mode settings are working great.
01-11-2013, 04:19 PM   #4
HSV
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One more observation about p-ttl:

1) if the external flash is on the hotshoe or p-ttl cable, it seems to overexpose often (a stop or two) when bouncing. Straight flash seems to be frequently proper exposed.
2) if the external flash is using wireless p-ttl (using the in-built flash to trigger and using an IR panel to block it's visible light), the exposure seems to be more "correct".

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