Flash over exposure problems.

Hi Guys,
I have a K100D and an AF-360FGZ flash gun. Everything appears OK when the camera is set to Auto Pict mode.
However, if I set to Aperture priority (to throw out a background at f1.4 for example), resultant pics come out madly overexposed.
Can anybody advise me/point me to a clearer source of info than the supplied manual.
This doing my head in, surely you must be able to use this kit in modes other than fully automatic.
Thanks in advance guys,
Gene Stevo.

Mattmatic's the flash guru around here (I just use an old manual one, so P-TTL is largely a mystery to me ), and he's done a flash guide.

See this thread for details: https://www.pentaxuser.com/forum/topic/Matt-Matics-Pentax-dSLR-Flash-Guide-9624/...

Dan

Normally this combination would have a tendancy to under expose so what you describe is rare. Start by checking the obvious:

1) Is the flash switched to P-TTL mode?
2) Has the camera and/or flash got the flash compensation turned up?

If this still doesn't solve the problem could you post an example picture here? You can resize it (800 pixels along the longest side works well in this forum) but leave the EXIF intact, this will let us see *exactly* what your camera and flash are saying to one another and will help in any diagnosis.

Hi hefty1,
Here are a couple of pics. The difference isn't as bad as I was getting this afternoon but you get the idea.
link

The explanation is simple. Stand further away from your subject, or use a smaller aperture.

You are too close to your subject for that flash to stand any chance of working correctly at f1.4, which is what you have set in Av mode. In auto picture mode, the camera has chosen f4.

I think the AF360FGZ has a scale on the bottom of the display. When the flash head is set to the same plane as the lens, it appears. It will give you the min and max distance you can use for that flash at your chosen focal length and aperture.

I am almost certain that you are much closer than the minimum distance indicated by that scale.

To get a better exposure in this scenario, bounce the flash off of the ceiling (not literally, tilt the head vertically) to increase the distance between flash and subject, and diffuse the light, or use a smaller aperture.

If I'm right, its user error and your gear is working as expected. User 0 - 1 Pentax Kit.

hefty1 has already mentioned that Pentax DSLR/Flash combinations usually tend towards underexposure, just like your Autopic image. It's slightly underexposed.

You need to learn to use this combo within its design constraints.

^^ I concur ^^

Bounce the light off the ceiling and you should see a huge improvement. Unfortunately this isn't down to limitations of the equipment, rather limitations in the Laws of Physics...

Hi All,
Huge thanks for your most welcome advice. I get the issue with the distance scale (esp after reading the sticky thread from Matt-Matics, nice one).
However this isn't the first time I've come unstuck. On my hols I tried to take some pics in some posh church in Piza. The pic was coming out almost black. I got so frustrated I turned the flash off and decided to try and stand still instead (not easy after an Italian liquid lunch:lol.
As you can see, predicably, the resultand image was unusable link All the pics where on Auto Pict. I suppose I need to read up a bit on using a flash gun as this is doing my condfidence no good at all (good book anybody?).
I'm almost frightened to get it out of the bag.
Cheers all.

Incidentaly, don't know if it makes a difference but:
Whatever picture I've ever taken with this flash/camera I've never witnessed the pre-flash that's supposed to occur with P-TTL.
Neither have I ever had the blinking symbols on the flash LCD panel or the cameras view finder to confirm that a correct exposure has been obtained.

The pre flash on my Metz is pretty damned quick. To see it, you have to be in ideal conditions. Normally, it's not noticeable.

Set the self-timer on the camera to the 2 second with mirror lock-up, and try the flash then. If the pre-flash is working okay, you will see this fire before the mirror flips up, then the main flash will go with the exposure. This should make it very easy to tell whether the pre-flash is firing as expected with P-TTL.

Dan

If the pre-flash is firing, you should see it through the viewfinder before the mirror flips and the exposure is made.

If you don't see it through the viewfinder, it's probably not firing.

Am I getting close?
Without a flash (built in or hot shoe) the camera adjusts shutter speed to suilt aperture in Av and vice versa in Tv.
This doesn't happen with a flash, in Av the shutter speed doesn't change to suit a change in apperture and aperture doesn't change to suit a change of shutter speed. Is this because the camera is adjusting the output from the flash to suit the other settings and exposure cock-ups are due to me being less than aware of the flashes limitations?

Incidentaly still not seeing a pre flash. The pop-up flash does a lot of snap, crackle & pop in v/dark situations but nothing with the AF360. In fact with v/little ambient light my pics come out horrible out of focus. Me expecting too much from my kit again?

Thanks for your continued patience. I'm determined to get this right, in fact there's a mental note not to allow any more dosh for kit till I've mastered what I've got already (the macro lens will just have to wait

It sounds like you should have a look through the manual(s) again . Also, I highly recommend to buy MattMatic's excellent Pentax Flash Guide:

Pentax Flash Guide

Well almost right but you got the idea, it depends in what mode the flash is (trailing curting, highspeed, etc.) that depends on how the camera reacts as well.
you can use the flash closer if you flip out the plastic defuser screen btw

If you use the AF360 in low light it use the spot-beam (it's called that i think) it shines a red grid on the subject that helps the camera to focus so it should be able to focus correctly.

I've just ordered MattMatic's flash guide.
No doubt I'll be back with even more daft questions...
Cheers guys,
Gene Stevo.