Originally posted by sinus007 Hi,
To answer some of the questions:
shooting in Av
ISO100
F2.8
1/60s
If you want to identify the cause of the error, use what I described above. Not open up the aperture. Not Av. Not long shutter times.
Originally posted by sinus007 The difference between P-TTL and A is about 2 stops.
That there is a difference between two completely different metering systems is to be expected.
In order to be able to analyze it really for you, you need to share the two raw files (not JPG).
We need to see the raw histograms. Only they can tell us, if the photo is correctly exposed.
Maybe you just like it a little darker and the light metering in the flash prefers darker outputs. Then this whole thread has a simple solution: To get your subjective preference in PTTL you always dial in -2 flash exposure compensation in the flash or on the camera.
Originally posted by sinus007 I mean, I can use A mode or I can find the right settings in M mode and get a more or less good lighting. But why to have P-TTL flash and not use the feature.
Misconception. The camera in M mode still means P-TTL at work.
You do need to understand something about maths: Normally without flash you have only three variables: Time & ISO & F-stop. To get really consistent results you should fix two (like ISO and Fstop in AV Mode) and let the little computer calculate just one: shutter times. One degree of freedom is good for predictability. If you turn on AutoISO in normal shooting mode you already have many, many correct exposure settings: all are combinations of ISO and shutter time.
Using a flash you get a
fourth variable into play! Strobe light output. Many people are not aware of that.
That is why I suggest using M-Mode on the camera, where you set ISO, shutter and F-stop. Because now PTTL can/must only adjust one thing left: flash output.
The worst thing you can do is use Tv or Av and AutoISO and Flash. Because the absolutely correct exposure now is hundreds of triplets of parameters, a three dimensional space of correct solutions.