Multiple exposures in DSLR´s._Why_not?

[Guest]

Archived from groups: rec.photo.digital (More info?)

Carlos <gutto@iis.com.br> writes:
>Why DSLRs don't take multiple exposures shots? Is there any technical
>limitation, like, sensor overheating, excessive noise, .... ?

There would be excessive noise if you tried to do it like a film camera
does, keeping the CCD in "exposing" state while the shutter is opened
and closed multiple times. The sensor accumulates dark current during
the entire time it is in this state, while it collects exposure
electrons only while the shutter is open, so the signal-to-noise of the
image would be degraded.

Instead, the camera *could* take several completely separate exposures
and then add them via software. But it would need enough buffer memory
on-camera to keep all of the exposures around before they were added.

Once the camera is taking multiple separate exposures, it just makes
more sense in most circumstances to write them as separate images and
combine them on a computer later, where you have much more control over
the process. So in-camera multiple exposure is of little use to most
photographers.

>My question is about the fact I don't want to make multiple exposure by
>software edition.

Why not?

Dave

 

[carlos]

Archived from groups: rec.photo.digital (More info?)

Dave Martindale wrote:
> Carlos <gutto@iis.com.br> writes:
>
>>Why DSLRs don't take multiple exposures shots? Is there any technical
>>limitation, like, sensor overheating, excessive noise, .... ?
>
>
> There would be excessive noise if you tried to do it like a film camera
> does, keeping the CCD in "exposing" state while the shutter is opened
> and closed multiple times. The sensor accumulates dark current during
> the entire time it is in this state, while it collects exposure
> electrons only while the shutter is open, so the signal-to-noise of the
> image would be degraded.
>
> Instead, the camera *could* take several completely separate exposures
> and then add them via software. But it would need enough buffer memory
> on-camera to keep all of the exposures around before they were added.
>
> Once the camera is taking multiple separate exposures, it just makes
> more sense in most circumstances to write them as separate images and
> combine them on a computer later, where you have much more control over
> the process. So in-camera multiple exposure is of little use to most
> photographers.
>
>
>>My question is about the fact I don't want to make multiple exposure by
>>software edition.
>
>
> Why not?
>
> Dave

Dave,
Thank you very much!!!!! Thank you, thank you and thank you again. You
give me an answer that satisfy my curiosity and all of you said make sense.
Why not make multiple exposure by software?
Well, I have being do it since 1993 (editing pics and others things),
not for professional, only by myself, like a hobby. I'm not a pro
photographer and have others attributions in my life. I'm so tired to
retouch photos in computer.
My reluctance is only about the work I will have to do and don't having
much time to do it. Oh, yes, I have social life out of computer. 🙂
Thank you again. I'm seeing that I will have to "make" time to do it.
I think I will have to compress 27 hours in a 24 hours day. LOL.
Regards,

--
gutto@iis.com.br

Carlos A. B. Coutinho
Rio de Janeiro, RJ
Brasil

 

[Guest]

Archived from groups: rec.photo.digital (More info?)

Dave Martindale wrote:

> Instead, the camera *could* take several completely separate
exposures
> and then add them via software. But it would need enough buffer
memory
> on-camera to keep all of the exposures around before they were added.

Technically, there only needs to be enough buffer memory for
two images. One is the image being taken, and the other is
the accumulated sum so far.

> Once the camera is taking multiple separate exposures, it just makes
> more sense in most circumstances to write them as separate images and
> combine them on a computer later, where you have much more control
over
> the process. So in-camera multiple exposure is of little use to most
> photographers.

Yes, indeed.

Isaac Kuo

 

[Guest]

Archived from groups: rec.photo.digital (More info?)

Sheldon wrote:
> Photoshop has taken the place of many things we used to do with film
> and processing. Actually, you are "processing" your photos in
> Photoshop, using many of the same techniques you used to use with
> film and chemicals. You just don't have to turn out the lights to do
> it.

Or worry about the cat drinking out of the fixer tray...

 

[Guest]

Archived from groups: rec.photo.digital (More info?)

mechdan@yahoo.com writes:

>> Instead, the camera *could* take several completely separate
>exposures
>> and then add them via software. But it would need enough buffer
>memory
>> on-camera to keep all of the exposures around before they were added.

>Technically, there only needs to be enough buffer memory for
>two images. One is the image being taken, and the other is
>the accumulated sum so far.

Yes, if you have enough precision in the "accumulated sum" buffer. But
to avoid numerical problems doing it this way, you'll need extra bits
for the intermediate results. It's probably still a win for 4 or more
images being added, compared to storing them all separately.

Dave

 

[Guest]

Archived from groups: rec.photo.digital (More info?)

In message <cur719$il0$1@mughi.cs.ubc.ca>,
davem@cs.ubc.ca (Dave Martindale) wrote:

>Yes, if you have enough precision in the "accumulated sum" buffer. But
>to avoid numerical problems doing it this way, you'll need extra bits
>for the intermediate results. It's probably still a win for 4 or more
>images being added, compared to storing them all separately.

If it's adding RAW images, 16 12-bit images can be added in a 16-bit
buffer.
--

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