K5 bounce flash overexposure - mystery solved! MUST READ!

Started Jun 7, 2011 | Discussions thread
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dtsui
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K5 bounce flash overexposure - mystery solved! MUST READ!
Jun 7, 2011

I had my K7, yes, its K7 and AF540FGZ sent to the Pentax factory in Japan to fix bounce flash overexposure problem. After 4 months in waiting and transit, they equipment came back without anything being fixed. Factory claimed they could not find any fault. My K7 actually has the same problem as K5. When the equipment came back from Japan to CR Kennedy (Pentax's agent) in Adelaide I had the chance the test it alongside a K5 and BOTH cameras displayed the same problem with bounce flash, in fact with two separate AF540, mine and a new one. I have come to the conclusion there is bug in the firmware across both cameras. They share the same PTTL algorithm.

Those of you who own a K5 or K7 and AF540 can try the following test to see if you can replicate the problem.

1. Set camera to M 1/125 f/5.6 ISO 250

2. Point your flash up at 75 degree, make sure the ceiling is not too high and is white in color.
3. If you have a zoom lens, set to 18mm or 17mm.
4. Take a shot of a subject at about 2 to 3m and note its exposure.

5. Change the zoom setting on the flash manually and take a shot at each step and note the exposure.

6. You should notice a progressive decrease in exposure as the flash zoom angle changes in steps from 16--> 19--> 24--> 34--> 48--> 58. Note the exposure at 58. It should be the best out of the lot.
7. Now set the lens to 55mm or 70mm.

8. Change the flash zoom angle in steps from 58--> 48--> 34--> 24--> 19--> 16. You should notice a progressive increase in exposure towards 16. Note the exposure at 19 or 16. It should be the best of the lot.

If you follow the test and can confirm the same results then the logical conclusions are:

1. The K5 and K7 PTTL algorithm applies a flash exposure compensation in bounce flash in accordance with the zoom setting on the flash unit.
2. The flash exposure compensation is the opposite of what is required.

To get around this problem with bounce flash, when you shoot at 18mm, manually set your flash to 58, and when you shoot at 70mm, manually set your flash to 16.

I do not understand why Pentax tries to deny the problem and fails to deliver a firmware upgrade for such a blatant and obvious mistake in their flagship camera.

David

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