Electronic Vs Mechanical Shutter

I have to say I'm not really sure how an electronic shutter even works,
but was wondering why dSLR cameras don't use them. At least the dSLRs
that I am aware of don't. Don't all if not most all video cameras use
some kind of electronic shutter?


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Chris W
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On Tue, 18 Mar 2008 16:01:17 -0500, Chris W wrote:

I have to say I'm not really sure how an electronic shutter even works,
but was wondering why dSLR cameras don't use them. At least the dSLRs
that I am aware of don't. Don't all if not most all video cameras use
some kind of electronic shutter?

Electronic shutters require some extra circuitry at each pixel to
store the charge accumulated while the electronic shutter was open.
Since the pixel is always sensitive to light, the charge accumulated
while the electronic shutter was open has to be stored somewhere while
it's being read off the sensor. That extra circuitry at each pixel
takes up space on the substrate that could otherwise be used to make
the photosensitive pixels larger.

A sensor that uses an mechanical shutter doesn't need that extra
circuitry, so the pixels can be larger, gather more light and be more
sensitive with less noise for the same sensor size. Of course,
without that extra circuitry to store the charge, the sensor is still
sensitive to light and will accumulate more charge while it's being
read off into the camera if there's still a light source on it. That's
why you need the mechanical shutter. If the sensor was still exposed
to light while it was being read off, you'd have ghosting and blurring
of the image because the entire sensor isn't read simultaneously. The
data is streamed off.

Some video cameras also have mechanical shutters of the same type as
was used with film motion picture cameras.

So the simple answer is that, all else being equal, a camera with a
mechanical shutter will have higher sensitivity and lower noise than
one with an electronic shutter. That comes at the expense of
simplicity and longevity.

Steve

In article , Chris W
wrote:

I have to say I'm not really sure how an electronic shutter even works,
but was wondering why dSLR cameras don't use them. At least the dSLRs
that I am aware of don't. Don't all if not most all video cameras use
some kind of electronic shutter?

the nikon d40, d50, d70 and d70s all had a combination electronic and
mechanical shutter which gave them the unique ability to have a faster
than usual flash sync. officially it was 1/500th, but by using a
non-nikon flash, it would sync at any shutter speed, all the way up to
1/8000th. unfortunately, they were more susceptible to blooming.

"nospam" wrote in message
...
In article , Chris W
wrote:

I have to say I'm not really sure how an electronic shutter even works,
but was wondering why dSLR cameras don't use them. At least the dSLRs
that I am aware of don't. Don't all if not most all video cameras use
some kind of electronic shutter?

the nikon d40, d50, d70 and d70s all had a combination electronic and
mechanical shutter which gave them the unique ability to have a faster
than usual flash sync. officially it was 1/500th, but by using a
non-nikon flash, it would sync at any shutter speed, all the way up to
1/8000th. unfortunately, they were more susceptible to blooming.

Thank you for those answers. I have had the same question on my mind.

In article , Steve says...

Electronic shutters require some extra circuitry at each pixel to
store the charge accumulated while the electronic shutter was open.
Since the pixel is always sensitive to light, the charge accumulated
while the electronic shutter was open has to be stored somewhere while
it's being read off the sensor. That extra circuitry at each pixel
takes up space on the substrate that could otherwise be used to make
the photosensitive pixels larger.

I would have thought that electronic shutters were implemented with some
kind of pixel level switch which would prevent the pixel from accepting
more charge when the switch was closed and would be able to discharge
the pixels - or something similar. Perhaps an electric field applied to
each pixel which would freeze the charge inside the pixels.
--

Alfred Molon
------------------------------
Olympus 50X0, 8080, E3X0, E4X0, E5X0 and E3 forum at
http://tech.groups.yahoo.com/group/MyOlympus/
http://myolympus.org/ photo sharing site

On Wed, 19 Mar 2008 09:57:26 +0100, Alfred Molon
wrote:

In article , Steve says...

Electronic shutters require some extra circuitry at each pixel to
store the charge accumulated while the electronic shutter was open.
Since the pixel is always sensitive to light, the charge accumulated
while the electronic shutter was open has to be stored somewhere while
it's being read off the sensor. That extra circuitry at each pixel
takes up space on the substrate that could otherwise be used to make
the photosensitive pixels larger.

I would have thought that electronic shutters were implemented with some
kind of pixel level switch which would prevent the pixel from accepting
more charge when the switch was closed and would be able to discharge
the pixels - or something similar. Perhaps an electric field applied to
each pixel which would freeze the charge inside the pixels.

That's sort of what they do, but they need extra electronics at each
pixel to do that. Even a pixel level switch, or something to apply a
field, or anything other than the actual photo sensor requires
additional circuitry that would take space away from the actual photo
sensor and decrease the sensor's light sensitivity.

Conceptually, it works like this: The pixels can either dump the
charge and start fresh or accumulate charge when photons hit them.
There's no "hold mode" for the actual pixel sensor that holds current
stored charge when more photons hit them. That's true for electronic
and mechanical shutters.

For the electronic shutter, before the beginning of exposure, charge
is dumped from the pixels and the pixel charge storage unit. I.e.,
think of them as being grounded out. Then at the beginning of
exposure, ground is disconnected, photons are allowed to create charge
on the pixels, which are connected to their storage unit so they
charge up the storage unit as well. Then after the specified exposure
time, the pixels are disconnected from their storage units. The
actual sensor pixels can be doing whatever they want with additional
photons while the storage units are read off. They'll probably very
quickly reach saturation and not store accumulate anymore. The
storage units are not light sensitive. So as additional photons hit
the sensor, they are unnaffected and can be read off without worrying
about smearing and ghosting the image.

For the mechanical shutter, at the beginning of exposure the pixel
charge is dumped, the shutter opens, the shutter closes and the pixels
are read. They are no longer receiving photons so they don't
accumulate anymore charge while they're being read. So they can be
read off without worrying about smearing and ghosting the image, and
without needing a charge holder that's not sensitive to light like the
electronic shutter needs. No need for non-light-sensitive charge
holder means more space available for light-sensitive pixels means
more sensitivity to light.

Steve

On Wed, 19 Mar 2008 09:57:26 +0100, Alfred Molon
wrote:

In article , Steve says...

Electronic shutters require some extra circuitry at each pixel to
store the charge accumulated while the electronic shutter was open.
Since the pixel is always sensitive to light, the charge accumulated
while the electronic shutter was open has to be stored somewhere while
it's being read off the sensor. That extra circuitry at each pixel
takes up space on the substrate that could otherwise be used to make
the photosensitive pixels larger.

I would have thought that electronic shutters were implemented with some
kind of pixel level switch which would prevent the pixel from accepting
more charge when the switch was closed and would be able to discharge
the pixels - or something similar. Perhaps an electric field applied to
each pixel which would freeze the charge inside the pixels.

Just to simplify the whole thing, no matter what you do for an
electronic shutter (store charge, stop pixels from accepting more
charge as photons hit them, whatever else you can think of) you need
additional non-light-sensitive circuitry *at the pixel* to do
something that a sensor designed for a mechanical shutter does not
neet. The additional circuitry has to be at the pixel because of the
way the charge is read off, i.e., not all pixels are read off the
sensor simultaneously. This additional, non-light-sensitive circuitry
at the pixel to implement the electronic shutter means that it's less
sensitive to light than if it didn't have that circuitry and instead
relied on mechanically shutting off the light.

Steve

On Tue, 18 Mar 2008 17:55:56 -0700, nospam wrote:

In article , Chris W
wrote:

I have to say I'm not really sure how an electronic shutter even works,
but was wondering why dSLR cameras don't use them. At least the dSLRs
that I am aware of don't. Don't all if not most all video cameras use
some kind of electronic shutter?

the nikon d40, d50, d70 and d70s all had a combination electronic and
mechanical shutter which gave them the unique ability to have a faster
than usual flash sync. officially it was 1/500th, but by using a
non-nikon flash, it would sync at any shutter speed, all the way up to
1/8000th. unfortunately, they were more susceptible to blooming.

Then there's the whole slew of P&S cameras that are able to sync up to
1/224,000th of a second exposures. 1/224,000th for flash duration, and
1/60,000th second for electronic shutter speed, without blooming. A far sight
better than any ancient 1/8000 second limitation. This of course is also without
exposing for any ambient light due to the agonizingly slow focal-plane shutters
which must remain open to sync with the 1/8000 flash speed. This huge drawback
of the ancient focal-plane shutter method completely blurs any portions of a
moving subject while waiting for the shorter duration flash to fire, making that
method's usefulness questionable and only in specific lighting situations. The
ambient light has to be reduced enough to avoid this, if you have any control
over it that is. These P&S cameras are now free of all those drawbacks and
limitations of last century's focal-plane shutter designs. The sensors of these
P&S cameras also capture the full frame in that one brief micro-exposure so
there's not any evidence of sensor-reading delays as the information is spooled
off, causing another type of banding problem with high-speed photography in most
all DSLR designs. This common DSLR data-banding defect in images of high-speed
subjects is due to banks of pixel data spooled off in independent chunks. In
these P&S cameras it is captured first, then spooled off in-total later. All
former problems with high-speed photography finally and completely circumvented.

http://chdk.wikia.com/wiki/Samples:_...%26_Flash-Sync

http://chdk.wikia.com/wiki/CameraFeatures

On Tue, 18 Mar 2008 17:55:56 -0700, nospam wrote:
In article , Chris W
wrote:
I have to say I'm not really sure how an electronic shutter even works,
but was wondering why dSLR cameras don't use them. At least the dSLRs
that I am aware of don't. Don't all if not most all video cameras use
some kind of electronic shutter?

the nikon d40, d50, d70 and d70s all had a combination electronic and
mechanical shutter which gave them the unique ability to have a faster
than usual flash sync. officially it was 1/500th, but by using a
non-nikon flash, it would sync at any shutter speed, all the way up to
1/8000th. unfortunately, they were more susceptible to blooming.

The same high-synch speeds are possible with a Pentax DSLR (any model)
with the correct flashgun (such as the Sigma 500 DG Super or the Pentax
Af-360fgz, plus many others).
It's not an electronic shutter in the camera, it's the flashgun strobing
quickly so that the whole sensor is exposed sequentially as the open
slit of the shutter passes the sensor.
It's the "HS sync" setting on your flashgun.
I would also hazard a guess that most of the DSLR cameras on the market
can do the same trick with the appropriate flashgun attached.

In article
, dj_nme
wrote:

the nikon d40, d50, d70 and d70s all had a combination electronic and
mechanical shutter which gave them the unique ability to have a faster
than usual flash sync. officially it was 1/500th, but by using a
non-nikon flash, it would sync at any shutter speed, all the way up to
1/8000th. unfortunately, they were more susceptible to blooming.

The same high-synch speeds are possible with a Pentax DSLR (any model)
with the correct flashgun (such as the Sigma 500 DG Super or the Pentax
Af-360fgz, plus many others).
It's not an electronic shutter in the camera, it's the flashgun strobing
quickly so that the whole sensor is exposed sequentially as the open
slit of the shutter passes the sensor.
It's the "HS sync" setting on your flashgun.
I would also hazard a guess that most of the DSLR cameras on the market
can do the same trick with the appropriate flashgun attached.

perhaps that's how it works on the pentax, but on the aforementioned
nikons, no special high speed sync mode is needed, and it does not even
require a special flash. the cameras use a combination electronic and
mechanical shutter -- the shutter is fully open at a more common sync
speed and then the sensor is read out at the faster speed.