[kdre]

@kdre

This would explain why some users never see this behaviour, some occasionally, some always - independend from camera model.

In my previous post I wrote that a german user has two identical pentax cameras (K20d) and two Metz 40 flashes.
On one camera the flashes overexpose when bounced.
On the other the flashes behave correctly and do not overexpose.

So, i believe that this cannot be flash related.

And btw: We are talking about the camera in "M" mode, NOT "P" or any other automatic mode.

[RKKS08]

To make things easier for me, I just copy the posting I just made in another thread:
https://www.pentaxforums.com/forums/pentax-flashes-lighting-technique/232301-...ml#post2481813

Copy is as follows:

There is one thing I forgot to tell. It is a bug in a range of Metz flashes, including the 40MZ series.

If you first take a picture with flash directly to the subject, and after that switch to bouncing, the flash display will still show the ISO correctly as set from the body. But internally there MAY BE a wrongly set ISO (to lowest setting) in the flash. Whether this will lead to over exposure or not, depends on aperture, distance, etc. This forum (and all German forums) are full with discussions of the problem. A quick fix is to recall program 0 (the actual settings) after switching the reflector to bounce mode.

Strangely enough, in German forums there are many postings where users own more than one copy of a Pentax DSLR, and they tell the problem does not exist with all of them. In one case it was even reported there was no error with a K-5, but after it was returned from service (sensor stains) the issue was there - they had not updated the ROM version!
So it probably is not really a bug, but some kind of incompatibility caused by very small tolerances during communication.

The issue was reported with K10D, K200D, K-x, K-7, K-5, and K-01.
With K-5 and K200D there are reports that there is no problem with some bodies.

One user send a 40MZ to the German Metz service for a test, and got it back with the following answer (rough translation to English by me):

...meanwhile we were able to test your configuration in respect to over exposures when bouncing. We can confirm the issue. After changing the flash mode to bouncing, obviously the ISO value set by the camera does not get recognized correctly anymore. The flash display still shows the correct value, but the flash auto function will now use a lower ISO value frequently causing over exposure. The effect will be more visible at higher camera ISO values.

RCL will delete the wrongly set ISO value, and with the next data exchange the correct ISO value will be used.

Because of these facts the problem cannot be solved by using a newer SCA adapter, or upgrading its ROM. It could only be fixed by a program modification of the flash itself, but the 40MZ series was not capable of a ROM update.

There would be a way to solve the problem by disabling the capabilty of the flash to detect bouncing mode. Then the mis-interpretation of the ISO value would not happen anymore. The drawback would be, that now the shown flash range would always be the one for direct flashing, not for bouncing. However, exposures would be correct for direct flashing as well as for bouncing.

This user asked Metz to disable the bouncing detect (2 micro switches), and they did it for free. He told, after that all problems were solved.