E-M5: Rattlesnaking explained

Started Jul 12, 2012 | Discussions thread
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Timur Born
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E-M5: Rattlesnaking explained
Jul 12, 2012

This was taken out of another thread where it would be off-topic and quickly get lost for those people who might be interested in rattlesnaking/chatter/aperture dance.

Anders W wrote:

Timur! If you have experimented with the chatter, it'd be nice if you could summarize in some pretty systematic fashion when this happens and not. I still don't have a clear view about that, only some loose indications.

I only own the 12-50 and 45/1.8, but for those two the chatter/rattlesnaking/aperture dance behavior of the E-M5 is rather clear and reproducible. Basically there are situations where the camera switches completely to rattlesnaking mode (aperture closing dynamically depending on brightness and EC settings).

From there you need to differentiate Movie mode (especially with recording stopped) from Stills modes (PASM).

Movie Mode

  • P and S settings always uses rattlesnaking mode, with fast changes of aperture when video recording is stopped and slow changes when video recording is active.

Exposure compensation preview is done by a combination of aperture and curves. Negative EC will close down the aperture, but going from negative back up to 0 or positive will not necessarily open up the aperture all the way again, until you (half)press the shutter.

  • A and M setting never use rattlesnaking mode, instead aperture is fixed exactly to the one the user sets up manually. Even for stills shooting (which is possible in Movie mode) this has the big advantage of getting a live DOF preview without having to hold down any buttons! Additionally you can improve face detection by dialing in a deeper DOF that way. Exposure compensation preview is completely done via curves, too.

  • During video recording any aperture changes happen only very slowly, which means that exposure changes also happen slowly. This makes aperture changes inaudible.

  • Focusing always is done using a wide open aperture when recording is stopped, but done at the currently active aperture when recording is running.

  • AEL (exposure lock) will keep the aperture from changing, unless you dial in negative exposure compensation.

  • Switching away from Movie mode to any stills mode also switches off rattlesnaking (unless you already had it in a Still mode before).

Stills modes (PASM)

  • Stills mode normally do not rattlesnake/chatter/aperture dance and exposure compensation preview normally done by curves only.

  • Pointing the camera towards a flickering light source, especially incandescent light bulbs (50 Hz here) will switch the E-M5 to rattlesnaking mode reproducibly and permanently until you switch off the camera. This may happen after something like only 2 seconds (light bulb) to several more seconds (quickly changing highlights and shadows inside the frame). I once made it switch by quickly wavering my hand in front of the lens, but it's not that easy usually.

Exposure compensation preview is done by a combination of aperture and curves. Negative EC will close down the aperture, but going from negative back up to 0 or positive will not necessarily open up the aperture all the way again, until you (half)press the shutter.

  • It doesn't matter which PASM mode you are using, but DOF preview (via Fn button) overrides the rattlesnaking.

  • AEL (exposure lock) will keep the aperture from changing, unless you dial in negative exposure compensation.

  • Focusing always is done using a wide open aperture.

You might well be right that it happens on some lenses although too quietly to be heard unless you are in quiet surroundings and pay attention. I think all my Pany lenses are indeed audible when they do it. But I am not yet sure about the Olys.

The 45/1.8 is very audible (as is my Fuji X10 btw, which always does it) and also very visible, the 12-50 is hardly audible at all, mostly because of its smaller wide open aperture and solid build (I'd say).

Fujifilm X10
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