K10D and P-TTL

Ok, dokay... think I have some answers

After a whole lot of "I wonder if I did..." questions and trial and error I think I have stumbled on something

* In most K10D modes the camera will always try to expose for the highlights. This is with the K10D flash setting at normal or wireless.

* When you enable the Slow Flash Sync setting on the K10D then the highlights are handled "normally"

* If you use the mode TAv then the camera will expose "normally", and not for the highlights.


So, here are a few suggestions for using all this knowledge:

{1} If you want general flash use, then set the mode to TAv and set the ISO range you want in the Fn menu. e.g. ISO100-1600. This will give you "point-and-click" style flash. The camera will very nicely balance the ambient and the flash and reflections are just blown out. Choose a shutter speed that is close to the focal length (because SR is disabled), and an appropriate aperture - the camera will pick a balancing ISO.

{2} If you want to contain the highlights then use the Av mode. Set your aperture and force the ISO. For indoor shots it is useful to turn off the flash, click the green button to see what the ambient ISO is, then override that (easy if you've changed the front wheel to do ISO in the custom menu) and choose an ISO setting one to two stops lower. So, if the camera says ISO1600, then choose somewhere between ISO400 and 800. The flash will do its work and the highlights (including reflections) will be contained as much as possible. This is amazing for wedding and fashion stuff because you retain the detail in a white dress Just shoot RAW if it's critical so you have some latitude later

It's worth mentioning that if you choose auto ISO then the camera will choose the lowest possible ISO - which usually results in a very hard and clinical flash output. But again, it's to contain the highlights in Av mode. Best to override that

{3} When shooting in a controlled environment - like a school play, party etc - where the lighting doesn't change much then use "M" on the camera and P-TTL on the flash. In this mode, you'll need to pick a suitable ISO rating that is going to give sensible results. (On my setup you hold down the OK button while moving the front wheel.) Choose an aperture and adjust the shutter speed so the K10D meter shows somewhere between -2 and -1Ev. The flash will fill in the rest and you'll get a nicely exposed shot... and again I think it will try and retain highlights


Additionally, it's worth mentioning again that you are usually best to bounce the light, or use wireless, and/or use a diffuser (if the distance allows it).

But the bottom line is - from what I see Pentax do seem to have put the right logic in there... they just haven't told you how to get to it properly

I'd appreciate it if others could try the TAv, Av, and M modes on camera to see if they experience the same results above. I'm off to try this with wireless P-TTL and see if it all holds together still...

Let's hope this helps
Matt

Thanks Matt, I would be interested to know how you get on with P-TTL in wireless mode.

Clarky - initial results with wireless P-TTL are that the camera modes work exactly as described above i.e. TAv and Av give differing results (partly down the ISO setting being different, but also apparently because of different metering methods for flash between modes).

I had also been playing around with which modes support the HS setting. Initial results are: Green, Av, and M support high shutter speeds. Personally, I would only use Av and M since the Green mode and flash will try and use the lowest ISO - which results in a very stark image.

Might have to do some practical tests and then I'll have enough info to write a complete book on the subject... but not enough time to write one
Matt

Thanks Matt. Much appreciated

Yep, I can confirm that the (my) K10D/AF360 combo returns results just as you describe them here - I also started following your original tests on the previous page but it was obvious after the first dozen or so that my results were again mirroring yours.

P-TTL in consistency shocker!

A little postscript (another )...
It may be that the K10D is designed to contain the highlights in all modes, and when you select a higher ISO rating the flash cannot be turned down enough by the camera and so some of the highlights naturally blow out.

Of course, as I detailed before you can use the "A" mode of the flash with a little trickery so you can have it all ways.

(And for the Metz 50MZ5/SCA3702, I also found you cannot use Auto ISO on the K10D - the Metz will think it's ISO100. You can use the front dial to manually adjust the ISO and the Metz will track the setting. Horses for courses )
Matt

To me, there seems to be a basic problem with compatability between the K10D and the 540 flash. Most of my photos turn out underexposed when using P-TTL.
Is the flashgun "fit for purpose"?

Is this problem occurring with the K20D?

Neil

Neil,
There are many reasons why this could be perfectly valid Have you read the sticky guide to P-TTL?
I can understand this is frustrating, but in my practical experience I rarely have a real issue with the AF540 & AF360. (The exposure has been consistent between the *ist-D and K10D, and don't expect the K20D will be any different).

If you have eliminated all the other possibilities I mentioned in the stick thread, then, as I've mentioned in this thread, the Pentax DSLR is aiming to retain the highlights. This behaviour is actually ideal for portraiture and wedding photography - but may lead to the overall exposure looking underexposed. (But more often than not, it'll be down to one of the other things I mentioned.)

As I said, try using it in TAv mode with auto ISO between 100 and 1600. I reckon you'll find your problems pretty well disappear
Matt

Dear MattMatic,

I would like to wish you a belated Happy Easter and thank you once again for your erudition, patience and kindness.

You are a great benefit to us all!

best regards

Bluewhistle
aka James who has been using auto on the flash gun with great results

Really appreciate the kind words James Nice to know that what I post is actually useful
Matt

This is a question about P-TTL and bounced flash.

Clearly, when the flash is bounced, the pre-flash goes via the same route as the main flash, and is subject to the same inverse square law and reflectivity losses.

So when the reflection from the pre-flash reaches the camera, which then does its metering, the intensity of the reflection will be lower than if the flash had been direct.

With less light coming back, presumably the camera tells the flash to increase its output.

So my question is this:

Given that the flash power is adequate*, despite the enroute losses, are any other adjustments required for correct exposure, or is it all taken care of?

_____________________
* and all other things being equal, with Matt's notes here and elsewhere in mind

All taken care of

It's equivalent to taken a photo of a subject further away - that's all.
(But bounced flash is nicer as it's diffused)
Matt

Yes, as I thought. Cheers, Matt.

Well I've tried some fill-in shots yesterday and it turned out quite well except for one thing (K10d, Tokina 28-70/2.8 and 360FGZ): flash set to HS, camera to Av. The shutter speed remained at 1/180s even though I changed the aperture. ISO set at 100, no automatic. No indication of overexposure or underexposure. Both camera and the flash switched to HS (well the flash was just 'showing' HS) when I used Tv and set manually the shutter speed above 1/180s. So Av was not working the same way as without the flash.

I can confirm your results.