mFT shutter action: some hypotheses, comments needed...

[lester11]

Polytropia and Guy Parsons have earlier (http://www.dpreview.com/forums/post/52418827) shown sound recordings of the shutter action of their E-M1 and E-PL5. I wanted to try and make sense of them on the way to trying to make sense of shutter shock.

The first schematic illustrates a possible 5-step shutter action, and then how it might match to the E-PL5 recording.




Hypothetical shutter release stages for mechanical mFT shutters




Annotated trace suggesting the positioning of the 5-stage hypothesised shutter action

This hypothesis for a mechanical mFT shutter imagines that there are two early substantial actions corresponding to peaks in the A1 and A2 areas, where A1 is the live view open shutter being released to close, and A2 is when the curtains hit their stop. Not too sure about this, since the recording trace suggests this takes around 0.025 secs -- quite slow, really. The rest of the action in areas B, C, and D, and their associated peaks, seem reasonably plausible.

Then, I wanted to model the electro-mechanical shutters of the E-M1 and the E-P5, which offer short "release shutter lags". I assumed that the "normal" release shutter lag corresponded to the 5-stage shutter action of the other mFT shutters, and this hypothesis is shown below.

The hypothetical action of the "short" release lag action assumes that the curtains are held electo-magnetically after they have been mechanically released. They have to be held *somehow* prior the exposure being made! And the mechanical action is then hypothesised to occur after the image is captured. Again, the shutter *somehow* needs to be latched open...

These hypotheses are followed by annotations of Polytropia's "normal" and "short" traces.



[ATTACH alt="Hypothetical 5-stage E-M1 E-P5 shutter release lag "normal" "]media_2740296[/ATTACH]
Hypothetical 5-stage E-M1 E-P5 shutter release lag "normal"





Hypothetical E-M1 and E-P5 shutter action, with short release lag




Annotated traces suggesting the positioning of the hypothesised 5-stage shutter action




Again, the hypothesised location of the peaks in the A2 area is less than certain, and in the "short" trace it is not at all obvious that there is any A2 noise at all.

The point of all this is to suggest that, in wondering what might be going on with shutter shock, it is the crash of the first curtain opening in the shutter box that is the only realistic candidate for the source of vibrations which might cause the characteristic double-ghost effect.

So, your comments most welcome!

--
Lester

 

[Guy Parsons]

OK I can see this is really worrying you...

I'll get to work again making some more recordings with my E-PL5 to see what I can learn, I can see that I need to do....

Like before 1/50 and 1/4000 to hopefully "see" the shutter run.

But this time both with a finger pushing the shutter button and also a radio remote initiating the shutter.

Then play with anti-shock in the mix to see how that has an effect.

Also need to make a second channel to record the flash timing, but first and second curtain and FP mode to see what that might tell me.

Maybe substitute an accelerometer for a microphone held hard against the body so stray noise that doesn't cause vibration is removed.

And then find some way to sync the vibration recording with the 1,000 fps video I can do to try and make sense of how the sound peaks relate to what we see in the video.

But sadly not soon as too many jobs happening taking too much time. Currently doing some dry-wall work at home, fitting simple drawer system to a large air-tight box that is my dry storage box for cameras, spraying and assembling a model box car for my proposed garden railway, plus all the usual home chores. I'm retired, so have plenty of time, ha ! (That's the late Edna Krabappel "ha").

Regards.... Guy

 

[lester11]

Hi Guy

Syncing video with sound would be great! Also, making an accelerometer trace, and throwing in an anti-shock interval! Heck, we might just learn something (smile)...

 

[lester11]

I've just seen the SLR Gear review of the Pen E-P1, and their (2009) detailed analysis of its shutter shock problem:

http://www.imaging-resource.com/PRODS/EP1/EP1BLUR.HTM

They show a very nice video of the complete shutter action, which is *not* a straightforward "open first curtain for exposure, close second curtain to end exposure, reset". They also explain how the double vertical ghost of a shocked image can be much more pronounced at the top of the image than at the bottom. That's interesting!

I was led there by their review of the Panasonic revised 14-140 lens:

http://slrgear.com/reviews/showproduct.php?product=1611

They make the observation that they've seen shutter shock in almost every mFT camera body they've tested. (Not just Oly bodies; all mFT bodies; hmmm...) The electronic curtain of the GX7 and GM1 eliminated shutter shock when engaged.

Now this is what is interesting. On Oly bodies with IBIS, the shock of the mechanical first curtain closing disturbs the (floating) sensor and the sensor image stabilisation fails to manage the vibration and displaced sensor properly. On the GX1 Panny body, it seems that the shock disturbs the (floating) lens assembly and the lens image stabilisation fails to manage the vibration and displaced lens element properly.

 

[secretworld]

From the article:

above, http://www.imaging-resource.com/PRODS/EP1/EP1BLUR.HTM

Because it is caused by the first shutter curtain reaching the bottom of its travel, the bottom of the sensor will see more of the effects of this vibration than will the top of the sensor, which is covered by the second curtain of the shutter relatively soon after the vibration begins (at least within the critical shutter speed range we're talking about). Because the image is inverted on the sensor plane, this means that the top of the image will show the most blur. Accordingly, if we saw equal blur at the top and bottom of the image within the critical shutter speed range, that meant we could safely discount it as user-caused blur, rather than anomalous blur caused by the shutter mechanism.

OMG this makes me realize I had shutter shock with my pana 14mm on a GH2. In a lot of shots it had blur and double images in the top of the frame. Wide open not to much when testing and only disappearing at f8-11. I never realised but the in between shots were in the shutter shock range. Must have been a copy with a loose focus element cause non of my other lenses showed it.

 

[Guy Parsons]

From the article:

above, http://www.imaging-resource.com/PRODS/EP1/EP1BLUR.HTM

Because it is caused by the first shutter curtain reaching the bottom of its travel, the bottom of the sensor will see more of the effects of this vibration than will the top of the sensor, which is covered by the second curtain of the shutter relatively soon after the vibration begins (at least within the critical shutter speed range we're talking about). Because the image is inverted on the sensor plane, this means that the top of the image will show the most blur. Accordingly, if we saw equal blur at the top and bottom of the image within the critical shutter speed range, that meant we could safely discount it as user-caused blur, rather than anomalous blur caused by the shutter mechanism.

OMG this makes me realize I had shutter shock with my pana 14mm on a GH2. In a lot of shots it had blur and double images in the top of the frame. Wide open not to much when testing and only disappearing at f8-11. I never realised but the in between shots were in the shutter shock range. Must have been a copy with a loose focus element cause non of my other lenses showed it.

In Oly land at least the early shutters run down the sensor, the later shutters run up the sensor, so that can cause confusion when trying to relate what happens in various cameras. That is, more shake seen at top or bottom of the image.

Regards..... Guy