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Re: [OM] Live view operation, was: E-thingy body recommendation

Subject: Re: [OM] Live view operation, was: E-thingy body recommendation
From: Moose <olymoose@xxxxxxxxx>
Date: Wed, 30 Jun 2010 15:18:23 -0700
On 6/30/2010 1:49 PM, Chuck Norcutt wrote:
> Umm, as I view that video
> <http://www.dpreview.com/reviews/olympuse520/page7.asp>  it seems to me that 
> the E-520 very much drops the mirror even in Imager AF mode.
>    

They were there, and presumably could hear/feel whether the mirror 
dropped. I have no reason to mistrust them. My experience of cameras 
I've had is that their tests are remarkably through and accurate.

All mirrorless digicams have a blackout of video feed between the time 
the shutter is pressed and the time the processed JPEG is displayed on 
the LCD screen. It's inherent in current technology, which requires a 
reset of the sensor and mechanical shutter operation for still shots. 
Still cameras with the ability to capture a still frame during video 
capture have a brief lacuna in the video when the still is taken for 
that reason (1 sec. on the 5DII). Pure video cameras don't, at least 
mine doesn't, as it simply captures a frame from the stream, but that's 
because the sensor system is different.

Certainly all mine have had blackouts of various length. With the G11, 
it is quite brief, but certainly there. With early digicams, it was 
sometimes tediously long. It's possible it isn't visible on the screen 
with short shutter speeds on some cameras with fast processing.

In the case of a DSLR, , the focal plane shutter usually has to close 
then open-close to capture the image. The usual process is that the 
shutter closes, the sensor is reset, the shutter is re-cocked, opens and 
closes for the exposure, then the second curtain is re-cocked with first 
curtain open for LV and second curtain open, ready to start the next 
cycle. The close, re-cock, expose, close cycle must briefly cover the 
sensor twice. So two blackouts of video feed from sensor for LCD screen 
occur.

> The E-620 seems to behave differently.  There's no blackout period.
> <http://www.dpreview.com/reviews/olympuse620/page8.asp>
>    

The 5DII has alternate LV "silent shooting" modes that use an electronic 
shutter, whatever that is, to eliminate the first close-open cycle for 
sensor reset. That would eliminate the first shutter related blackout. 
If processing of the JPEG for screen viewing is fast enough, the second 
curtain blackout might not be visible. Remember, by default, unless you 
change it, the first thing seen after the shot is taken is the captured 
image, not live feed.

Perhaps the E-620 is doing something similar. Hard to tell from the 
static DPR test subject. You'd think 1/20 sec, plus curtain travel time 
would show on the video, but if the video frame rate of the screen is 
slow, it might not.

It could also simply hold the existing screen image for moment, to cover 
the blackout, a cosmetic solution. Oly will never tell. One could try 
testing by taking a long exposure on an E-620. IF the LCD blacks out 
during the actual exposure, the lack of blackout on shorter exposures 
may be simply fast image processing. If it doesn't black out, they are 
'cheating'.

In any case, shutter operation does mean at least one, and usually two, 
breaks in sensor availability for live image feed to the LCD, even if 
the mirror doesn't flap.

Moose
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