G9ii Autofocus while Constant Preview is On

[MFT Guy]

With the Constant Preview feature On and the camera in A mode and the aperture of the Lumix f1.7 lens set (in camera) to f4.0 does the AFS autofocus operate as I shoot while the lens returns briefly to f1.7 or instead at f4.0 as I press the shutter release? What about AFC?

The reason I care: my Lumix 25mm f1.7 seems to exhibit a slight focus shift, most evidently appearing at f4.0. If Constant Preview is On and autofocus truly is performed while the lens is at selected shooting aperture then focus shift is 'corrected for'. My brief testing suggests that is the case.

 

[alcelc]

No knowledge on G9-2 nor the 25 f/1.7.

However, AFAIK when Constant Preview is enabled, the lens would be physically set at the used f/stop. Panny uses to call it Preview (Constant Preview is to activate Preview mode).

Usual LV will simulate an image upon the sensor data which is taken from wide opening of the lens. The simulated image (lightness) is simulated from the estimation of the used f/stop & shutter speed. As Preview will simulate an image upon information on actual f/stop used, it will usually be much closer to the output to be taken.

Under very complicated lighting conditions, specially on older models that their LV are more primitive, I would call up Preview for more precise setting.

Hence, I am not surprise with your finding.

But if you would shoot at 0ev metering and f/1.7 would actually be used, I guess Preview would do nothing.

 

[MFT Guy]

With Constant Preview 'on', during half-press the aperture *usually* remains at the f-stop chosen by the user for the exposure. However, I noticed that sometimes, maybe 10%, the camera opens the aperture one or more f-stops, not necessarily to max aperture, during half-press, apparently to better seek focus for a difficult subject. Same behavior using both AFS and AFC focus control.

I used the Lumix 25mm f1.7 lens on my G9ii to investigate the issue. I could see the position of its aperture blades by looking from the front.

The behavior I describe is good for me - it seems to 'correct' the focus shift I have sometimes noticed, making me more willing to trust this lightweight, fast lens. The appearance in Playback is a close match to what I saw in the viewfinder as I prepared to shoot. I shoot mostly in A mode with Auto ISO.

 

[alcelc]

With Constant Preview 'on', during half-press the aperture *usually* remains at the f-stop chosen by the user for the exposure.

On my lower end Pannys (from G1, GX1, GX7, GX85, GX9 & G85), it will be so only in M mode. Because in M mode, Preview (if CP = ON) is the default viewing mode instead of LV.

Under A/S/P, when CP = ON, I can hit a fn key, which having Preview mapped to, to activate Preview on ad hoac basis. It means that Preview will replace LV (f/stop opens/closes to the set f/stop to obtain the data to simulate an image) for exposure setting/DoF guidance. Preview will be cancelled and will then return to LV mode on half pressing of shutter button or hit the Preview assigned fn key!

However, I noticed that sometimes, maybe 10%, the camera opens the aperture one or more f-stops, not necessarily to max aperture, during half-press, apparently to better seek focus for a difficult subject. Same behavior using both AFS and AFC focus control.

AFAIK Preview is independent from AF.

I used the Lumix 25mm f1.7 lens on my G9ii to investigate the issue. I could see the position of its aperture blades by looking from the front.

The behavior I describe is good for me - it seems to 'correct' the focus shift I have sometimes noticed, making me more willing to trust this lightweight, fast lens. The appearance in Playback is a close match to what I saw in the viewfinder as I prepared to shoot. I shoot mostly in A mode with Auto ISO.

Not sure how CP (actually Preview mode) will work on G9-2. On my Pannys when the shutter speed will be @ 0.5" or slower, the refresh rate of Preview will become laggy to reflect the Shutter Speed effect. The slower the shutter speed the more laggy of the image in evf/LCD. It could make operation nearly impossible.

Therefore under very low lighting condition I shall use Preview to monitor the exposure only under P/S/A mode and shall cancel it for composition, focusing and shooting. Under M mode, I shall disable CP for those situations, activate CP for exposure setting only. Luckily my lenses do not suffer much on focus breathing .