soldbear wrote:
> Last night I took some test photos.
>
> Common settings:
> - Body: K10D on tripod, triggered by wired remote control
> - Exposure: manual - f/5.6, 1/60 sec
> - ISO Speed: 200
> - Metering mode: Pattern
> - Lens: Sigma 18-50 mm f/2.8 DC EX
> - Flash: AF-540 FGZ P-TTL mounted on camera body
>
> I toggled between P-TTL and A.
>
> Below are some results, JPEG lifted directly from the camera, no
> post-processing.
>

I think I know why you are experiencing flash disappointment - if you take a look at the large versions of these two images, and examine the EXIF data in PhotoMe, you will see that the shots are both taken with the camera in manual exposure mode - this is fine for the standard "A" setting, which uses the sensor in the flash to squelch the light output... but for the P-TTL system to work, the camera and flash have to communicate both aperture and flash output - when you shoot with the camera metering system on manual the P-TTL flash will not receive the exposure and aperture data it needs to control the output - try again with the flash on P-TTL and the camera set on Aperture priority, so that the camera and flash can communicate the aperture settings and the flash output.

> Auto-2:
>
> http://farm4.static.flickr.com/3297/3212760897_5eb658643b.jpg
>
Here is the EXIF data from the full-sized image:
Light violin shot:

File type: JPEG
File size: 3,150.1 KB
Creation date: 1/20/2009 00:48
Last modification: 1/20/2009 17:18
Make: PENTAX Corporation (http://www.pentax.com)
Camera: PENTAX K10D
Lens: SIGMA 18-50mm F2.8 EX DC Macro
Software: K10D Ver 1.20
Dimension: 3872 x 2592 px (10 MP, 3:2)
Focal length: 40 mm (equiv. 60 mm)
Aperture: F5.6
Exposure time: 1/60"
ISO speed rating: 200/24°
Program: Manual
Metering Mode: Pattern
White Balance: User-Selected
Focus Mode: AF-S
Image Stabilizer: not ready
Noise Reduction: Off
Flash: Flash fired, compulsory flash mode

>
> PTTL-2:
>
> http://farm4.static.flickr.com/3425/3213606416_5cdb6c1c1d.jpg
>
Here is the EXIF data for this shot:
Dark violin shot:

File type: JPEG
File size: 2,780.7 KB
Creation date: 1/20/2009 00:48
Last modification: 1/20/2009 17:16
Make: PENTAX Corporation (http://www.pentax.com)
Camera: PENTAX K10D
Lens: SIGMA 18-50mm F2.8 EX DC Macro
Software: K10D Ver 1.20
Dimension: 3872 x 2592 px (10 MP, 3:2)
Focal length: 40 mm (equiv. 60 mm)
Aperture: F5.6
Exposure time: 1/60"
ISO speed rating: 200/24°
Program: Manual
Metering Mode: Pattern
White Balance: User-Selected
Focus Mode: AF-S
Image Stabilizer: not ready
Noise Reduction: Off
Flash: Flash fired, compulsory flash mode

If you think about it for a minute, you will understand that the Program TTL system has to have a two-way data flow between the camera and the flash - by setting the camera exposure system to manual, the flash loses the data that it needs to adjust the light output corresponding to the aperture set on your lens... as you have discovered, the flash works perfectly in Auto (not P-TTL) mode when the camera is set on manual exposure, and the flash is set for the same aperture as the camera lens, because the sensor built into the flash is controlling the light output - not the sensor built into the camera.

For P-TTL to work properly, the sensor in the camera has to control the flash output - and it will not do this when the camera is set on manual exposure - this combination just won't work, and it is not the fault of the camera or the flash - it is just a matter of incompatible mode settings.

Try shooting the same scene with the camera in aperture priority mode, and the flash in P-TTL, and I am certain that you will be much happier with the P-TTL mode.

Norm.