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I have a Panasonic Lumix DMC-FZ20 camera and have been taking some long
exposure shots of 8 second (lightning).

The camera take another 8 seconds to process the pictures (at which time the
lightning strikes!)

Can anyone explain why this is, and do all digital cameras behave the same?
If not then which are the fatest.

Ta

"Wills" <(E-Mail Removed)> schreef in bericht
news:(E-Mail Removed). ..
>I have a Panasonic Lumix DMC-FZ20 camera and have been taking some long
> exposure shots of 8 second (lightning).
>
> The camera take another 8 seconds to process the pictures (at which time
> the
> lightning strikes!)
>
> Can anyone explain why this is, and do all digital cameras behave the
> same?
> If not then which are the fatest.
>
> Ta

It's prob. to do with (in camera) long exposure noise reduction.
Turn it off and look at the differences.
Aad

On Tue, 13 Sep 2005 11:14:13 +0100, Wills
<(E-Mail Removed)> wrote:

>I have a Panasonic Lumix DMC-FZ20 camera and have been taking some long
>exposure shots of 8 second (lightning).
>
>The camera take another 8 seconds to process the pictures (at which time the
>lightning strikes!)
>
>Can anyone explain why this is, and do all digital cameras behave the same?
>If not then which are the fatest.

It's a technique called "dark frame subtraction", and most
cameras do this for long exposures. The noise generated by
the sensor builds up as the time increases in a way that's
consistent for the particular sensor in the particular
situation in which it's being used. After the "real"
exposure finishes the camera makes another identical
exposure but with the shutter closed - the "dark frame" -
which has the same noise pattern as the real exposure. This
is then subtracted from the original, cancelling most of the
noise without hurting the image detail.


--
Regards

John Bean

Thanks. That's something on the lines I was thinking.
Unfortunaly it's not possible to switch off noise reduction, reducing it
does nothing.

I have a friend who has a Nikon D100, which gives control back 'immediately
it finishes saving, but there's no way I can afford a D100 and the selection
of lenses of 35 -400mm equiv!

However I do have a wide selection of Pentax lens, so if some kind reader
has a Pentax *ist DS, perhaps they could let know if there is a considerable
recoverey time on on of these cameras.

Thanks
> > I have a Panasonic Lumix DMC-FZ20 camera and have been taking some long
> > exposure shots of 8 second (lightning).
> >
> > The camera take another 8 seconds to process the pictures (at which time
> > the lightning strikes!)
> >
> > Can anyone explain why this is, and do all digital cameras behave the
> > same? If not then which are the fatest.
>
> It's a technique called "dark frame subtraction", and most cameras do this
> for long exposures. The noise generated by the sensor builds up as the
> time increases in a way that's consistent for the particular sensor in the
> particular situation in which it's being used. After the "real" exposure
> finishes the camera makes another identical exposure but with the shutter
> closed - the "dark frame" - which has the same noise pattern as the real
> exposure. This is then subtracted from the original, cancelling most of
> the noise without hurting the image detail.
>
>

On Thu, 15 Sep 2005 17:06:14 +0100, News Will
<(E-Mail Removed)> wrote:
>However I do have a wide selection of Pentax lens, so if some kind reader
>has a Pentax *ist DS, perhaps they could let know if there is a considerable
>recoverey time on on of these cameras.

I also have a DS :-)

Dark frame subtraction is done by default for exposures
longer than a second but it can be turned off if you so
desire - first item in the Custom Menu: "Noise rediction"
on/off.


--
Regards

John Bean

John Bean <(E-Mail Removed)> wrote:

> I also have a DS :-)

I DON'T have a DS, but am considering getting one.

Perhaps you can tell me, how long after a 8+second exposure, before you can
take another picture.

> Dark frame subtraction is done by default for exposures longer than a
> second but it can be turned off if you so desire - first item in the
> Custom Menu: "Noise rediction" on/off.
Unfortunately this is not available on the Lumix

Ta

On Thu, 15 Sep 2005 18:42:56 +0100, News Will
<(E-Mail Removed)> wrote:

>John Bean <(E-Mail Removed)> wrote:
>
>> I also have a DS :-)
>
>I DON'T have a DS, but am considering getting one.

I used "also" because I have a DS as well as a Panasonic,
not because I thought you had a DS.

>
>Perhaps you can tell me, how long after a 8+second exposure, before you can
>take another picture.

I thought I already had. I already explained that the delay
is caused by the dark frame subtraction (noise reduction)
process, so ...

>
>> Dark frame subtraction is done by default for exposures longer than a
>> second but it can be turned off if you so desire - first item in the
>> Custom Menu: "Noise rediction" on/off.

.... if you turn it off there's no delay. Hope that's
clearer.

>Unfortunately this is not available on the Lumix

Yes, but you asked about the DS...

--
Regards

John Bean

[Posted and mailed]

John Bean <(E-Mail Removed)> wrote:

> On Thu, 15 Sep 2005 18:42:56 +0100, News Will <(E-Mail Removed)>
> wrote:
>
> > John Bean <(E-Mail Removed)> wrote:
> >
> > > I also have a DS :-)
> >
> > I DON'T have a DS, but am considering getting one.
>
> I used "also" because I have a DS as well as a Panasonic, not because I
> thought you had a DS.
>
> >
> > Perhaps you can tell me, how long after a 8+second exposure, before you
> > can take another picture.
>
> I thought I already had. I already explained that the delay is caused by
> the dark frame subtraction (noise reduction) process, so ...
>
> >
> > > Dark frame subtraction is done by default for exposures longer than a
> > > second but it can be turned off if you so desire - first item in the
> > > Custom Menu: "Noise rediction" on/off.
>
> ... if you turn it off there's no delay. Hope that's clearer.
>
> > Unfortunately this is not available on the Lumix
>
> Yes, but you asked about the DS...

It's been a long hot sticky day!
Thanks very much, I hope to have a DS soon :-)

Willie

John Bean <(E-Mail Removed)> wrote:

> On Thu, 15 Sep 2005 18:42:56 +0100, News Will <(E-Mail Removed)>
> wrote:
>
> > John Bean <(E-Mail Removed)> wrote:
> >
> > > I also have a DS :-)
> >
> > I DON'T have a DS, but am considering getting one.
>
> I used "also" because I have a DS as well as a Panasonic, not because I
> thought you had a DS.
>
> >
> > Perhaps you can tell me, how long after a 8+second exposure, before you
> > can take another picture.
>
> I thought I already had. I already explained that the delay is caused by
> the dark frame subtraction (noise reduction) process, so ...
>
> >
> > > Dark frame subtraction is done by default for exposures longer than a
> > > second but it can be turned off if you so desire - first item in the
> > > Custom Menu: "Noise rediction" on/off.
>
> ... if you turn it off there's no delay. Hope that's clearer.
>
> > Unfortunately this is not available on the Lumix
>
> Yes, but you asked about the DS...

It's been a long hot sticky day!
Thanks very much, I hope to have a DS soon :-)

Willie

On Thu, 15 Sep 2005 19:27:20 +0100, News Will
<(E-Mail Removed)> wrote:
>It's been a long hot sticky day!

I blame age when I do it :-)

>Thanks very much, I hope to have a DS soon :-)

It's a nice camera, you'll like it - especially if you
already have some nice Pentax lenses.


--
Regards

John Bean