Panasonic 20/1.7 underexposes in low light

[Peter Klein]

Folks: I have noticed several times that in low tungsten light, my 20/1.7 and G1 significantly underexposes the picture. I'm not talking about high contrast scenes where a bright area or light source fools the meter. I'm talking about fairly low contrast scenes getting underexposed by about two full stops.

For example, the first picture below is close to correctly exposed. No light sources in the frame, no huge contrast differences. But I shot about 20 pictures in the sequence, and all but three of them were grossly underexposed, like the second example. The correct exposure was about 1/20 at f/1.7 (ISO 800), but the camera was mostly exposing at 1/60-1/100.

I've read about this issue numerous times online. Someone once told me not to use evaulative metering with low light, so I was using center-weighted aperture priority with the lens wide open. Does anyone know how to make the camera behave in these conditions (short of just giving up on the internal metering and going full manual)?

 

[jsnack]

Use spot metering. I've found it to work well in scenes with neutral light. Evaluative metering is actually better for scenes with varying contrast.

 

[Peter Klein]

I've added an example of how most of the pictures turned out--very underexposed.

It's really interesting how this lens behaves. I wonder why it does that. The G1 is usually very good at exposing properly. But low tungsten light with this lens seems to consistently underexpose, with both evaluative and center-weighted metering. As you can see from the photos, adjusting the camera was not an option, as my left hand was occupied.

It looks like this was discussed here about a year ago. In fact, I posted in the thread! I'd forgotten all about it. Similar advice was given, use spot metering for low artificial light.
http://forum.getdpi.com/forum/showthread.php?p=269747

Does anyone have any additional experience or information regarding this issue?

--Peter

 

[deejjjaaaa]

Does anyone know how to make the camera behave in these conditions

use UniWB to get a histogram close to the real raw histogram and then you can use a proper correction to your camera's exposure

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camera meters/displays histogram under tungsten lamps (note exposure correction is +2) :

http://www.libraw.su/sites/libraw.su/files/images/red-camera.png

later the real data from the same raw file :

http://www.libraw.su/sites/libraw.su/files/images/red-raw.png

 

[Pat Donnelly]

We expect that our sensors will respond to the amount of light correctly, but the black and white sensor that is in our cameras may not detect certain colour temperatures in the same way as most other temperatures? The consistency suggests that this is a sensor fault?

That it is specific to one lens is unlikely?

The great thing about digitals, especially those with excellent lcd displays, is that exposure and focus checking is possible. I am a big fan of manual (focus and exposure) lenses for many reasons and I suppose I can now add this as another reason? The lcd screen should be adjustable via the menu, sorry, I hate the menues too, to show relative exposure with an AF lens? I have an EP-1 and no other m4/3.

 

[Peter Klein]

Thanks, Pat, but it appears that this lens does behave uniquely. In the old thread I posted, someone actually tested both the kit zoom and the 20/1.7, and found that only the 20/1.7 underexposed in artificial light. Another post I read somewhere else stated that the Leica/Panny 25/1.4 didn't do it, either.

 

[Pat Donnelly]

Sorry, Peter!

Is it a coating issue that is set off by Tungsten? Never heard of one, admittedly. Impossible to get around too.

Any progress?

 

[Peter Klein]

No idea why it happens, but spot metering does the trick. Just have to remember it when the time comes.