Why do digital cameras need shutters?

In message ,
Alan Browne wrote:

Steve wrote:

I hope this isn't a silly question. Is it impossible or too expensive to
turn the sensor on and off or something instead of a mechanical shutter?
Just wondering.

In addition to the other replies I believe the camera manufacturers also
use the shutter as a black reference to measure sensor native noise.

For "noise reduction mode" for long exposures; yes. For normal
purposes, cameras may use blind pixel borders on the sensor. The 20D,
for example, has a vertical strip of 74 pixels wide on the left side of
the image, and a horizontal strip 12 tall on the top. The data from
these is where the JPEG engine and RAW converters get their black values
from (and they serve a s a noise sample as well). They are actually
contained in the RAW .cr2 file, and black is left with the offsets still
in them and in the exposed image (average is typically 128.2 to 128.4).

The Nikon D70 "electronically" shutter flash syncs up to 1/500 which is
on the "closing" side of the cycle, and I think that should be standard
on all high end DSLR's.

1/500 sync would be great; it would reduce the ambient softness when I
use flash fill with long focal lengths.
--


John P Sheehy

Alan Browne wrote:
Jeremy Nixon wrote:

The Nikon D70 "electronically" shutter flash syncs up to 1/500 which is
on the "closing" side of the cycle, and I think that should be standard
on all high end DSLR's.

You can only do that with a CCD sensor, not with a CMOS.

I didn't know that. Source?

You can technically have an electronic shutter with CMOS, but not without
compromise; it's a pretty standard feature of CCD sensors. A quick google
turned up:

http://www.dalsa.com/shared/content/..._Litwiller.pdf

Page 2 of that article has a pretty good description of the difference.

--
Jeremy |

On Thu, 23 Feb 2006 02:28:06 GMT, opined:

For "noise reduction mode" for long exposures; yes. For normal
purposes, cameras may use blind pixel borders on the sensor. The 20D,
for example, has a vertical strip of 74 pixels wide on the left side of
the image, and a horizontal strip 12 tall on the top. The data from
these is where the JPEG engine and RAW converters get their black values
from (and they serve a s a noise sample as well). They are actually
contained in the RAW .cr2 file, and black is left with the offsets still
in them and in the exposed image (average is typically 128.2 to 128.4).

That's fascinating information, John, thanks for passing it on.
--
W
. | ,. w , "Some people are alive only because
\|/ \|/ it is illegal to kill them." Perna condita delenda est
---^----^---------------------------------------------------------------

In article ,
"Steve" wrote:

How can it be inaccurate? Isn't there a processor clock that could time
"shutter speed"? Just wondering and stubborn, too.

The clock would be accurate enough, but the response time of the sensor
(both on and off) might not be.

Merritt