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Nikon D100 long exposures - Help!

 
 
Anonymous
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      08-14-2004
Hi,

I just tried some long (8sec-30sec) long exposures with my D100 and am very
disappointed with and confused by the results.

On a number of the images (especially those at 15 and 30 seconds) there are
a TON of specular highlights (blown out pixels?) ALL OVER the image. My
D100 works perfectly otherwise, both before and after this particular shoot.
It's not an issue of dust on the sensor.

Is there something about long exposures that digital SLR's don't do well
with?

TIA---


 
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David J Taylor
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      08-14-2004
Anonymous wrote:
> Hi,
>
> I just tried some long (8sec-30sec) long exposures with my D100 and
> am very disappointed with and confused by the results.
>
> On a number of the images (especially those at 15 and 30 seconds)
> there are a TON of specular highlights (blown out pixels?) ALL OVER
> the image. My D100 works perfectly otherwise, both before and after
> this particular shoot. It's not an issue of dust on the sensor.
>
> Is there something about long exposures that digital SLR's don't do
> well with?


There is a problem with "dark current" causing these speckles. Most
cameras have a "noise reduction" or "dark frame subtraction" mode to
compensate for this. It may double the total exposure time, though. Read
your manual.

Cheers,
David


 
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Jeremy Nixon
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      08-15-2004
Anonymous <(E-Mail Removed)> wrote:


> Is there something about long exposures that digital SLR's don't do well
> with?


Yes. You can enable dark-frame subtraction noise reduction to reduce the
noise; it'll be called "long exposure noise reduction" in the menu, and
will result in processing time after each shot equal to the exposure time
of that shot (during which you will not be able to take another shot).
It does an excellent job, since this kind of noise is far easier to clean
up than the random sensor noise we all know and love.

--
Jeremy | http://www.velocityreviews.com/forums/(E-Mail Removed)
 
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Anonymous
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      08-16-2004
Jeremy,

I'm not sure I follow you. I double checked the D100 manual and under "Long
Time Exposures" all it says is to turn on Custom Setting 4 which increases
exposure time (similar to reciprocity failure in traditional film). It says
nothing about reducing the "speckles" which come with long exposures.

Can you clarify your post below?

Thanks---


"Jeremy Nixon" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
> Anonymous <(E-Mail Removed)> wrote:
>
>
> > Is there something about long exposures that digital SLR's don't do well
> > with?

>
> Yes. You can enable dark-frame subtraction noise reduction to reduce the
> noise; it'll be called "long exposure noise reduction" in the menu, and
> will result in processing time after each shot equal to the exposure time
> of that shot (during which you will not be able to take another shot).
> It does an excellent job, since this kind of noise is far easier to clean
> up than the random sensor noise we all know and love.
>
> --
> Jeremy | (E-Mail Removed)



 
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Jeremy Nixon
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Posts: n/a
 
      08-16-2004
Anonymous <(E-Mail Removed)> wrote:

> I'm not sure I follow you. I double checked the D100 manual and under "Long
> Time Exposures" all it says is to turn on Custom Setting 4 which increases
> exposure time (similar to reciprocity failure in traditional film). It says
> nothing about reducing the "speckles" which come with long exposures.


I don't have a D100, so I don't know what its Custom Setting 4 is. On the
D70, it's the second option in the shooting menu, labeled "Long exp. NR"; it's
not in the Custom Settings menu.

I've no idea what it's getting at with increasing exposure time; there is no
reciprocity failure with digital. And the D70's Custom Setting 4 is to enable
the autofocus assist light, which I assume isn't what you're referring to.

--
Jeremy | (E-Mail Removed)
 
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Anonymous
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      08-16-2004
Jeremy,

Here's what my D100 manual says on page 82: "To reduce noise at shutter speeds of 1/2 second or slower, select ON for Custom Setting 4. Note that this increases the time needed to process photographs." I assume this means the time needed to process the image/reduce the speckles AFTER it is shot, not an increase in shutter time itself.

Page 149 goes into more detail on this, but effectively says the same thing. I assume the increased time is for the D100/D70 to fill in the blown out pixels with similar information from around them...



"Jeremy Nixon" <(E-Mail Removed)> wrote in message news:(E-Mail Removed)...
> Anonymous <(E-Mail Removed)> wrote:
>
> > I'm not sure I follow you. I double checked the D100 manual and under "Long
> > Time Exposures" all it says is to turn on Custom Setting 4 which increases
> > exposure time (similar to reciprocity failure in traditional film). It says
> > nothing about reducing the "speckles" which come with long exposures.

>
> I don't have a D100, so I don't know what its Custom Setting 4 is. On the
> D70, it's the second option in the shooting menu, labeled "Long exp. NR"; it's
> not in the Custom Settings menu.
>
> I've no idea what it's getting at with increasing exposure time; there is no
> reciprocity failure with digital. And the D70's Custom Setting 4 is to enable
> the autofocus assist light, which I assume isn't what you're referring to.
>
> --
> Jeremy | (E-Mail Removed)

 
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Jeremy Nixon
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Posts: n/a
 
      08-16-2004
Anonymous <(E-Mail Removed)> wrote:

> Here's what my D100 manual says on page 82: "To reduce noise at shutter
> speeds of 1/2 second or slower, select ON for Custom Setting 4. Note
> that this increases the time needed to process photographs." I assume
> this means the time needed to process the image/reduce the speckles
> AFTER it is shot, not an increase in shutter time itself.


Yes, that's the option you want, and that is indeed what the increased
time is for.

> Page 149 goes into more detail on this, but effectively says the same
> thing. I assume the increased time is for the D100/D70 to fill in the
> blown out pixels with similar information from around them...


What it's actually doing is taking a "black" frame (shutter closed) for
the same duration as the picture you just took; thus, the black frame,
taken under the same conditions as the real picture, has the same long
exposure noise as the real picture. It's then a simple mathematical
process to use the dark frame to remove the noise from the picture using
subtraction.

--
Jeremy | (E-Mail Removed)
 
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Marli
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      08-17-2004
Even my Minolta 7i has this, it works a treat..


"Jeremy Nixon" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
> Anonymous <(E-Mail Removed)> wrote:
>
> > Here's what my D100 manual says on page 82: "To reduce noise at shutter
> > speeds of 1/2 second or slower, select ON for Custom Setting 4. Note
> > that this increases the time needed to process photographs." I assume
> > this means the time needed to process the image/reduce the speckles
> > AFTER it is shot, not an increase in shutter time itself.

>
> Yes, that's the option you want, and that is indeed what the increased
> time is for.
>
> > Page 149 goes into more detail on this, but effectively says the same
> > thing. I assume the increased time is for the D100/D70 to fill in the
> > blown out pixels with similar information from around them...

>
> What it's actually doing is taking a "black" frame (shutter closed) for
> the same duration as the picture you just took; thus, the black frame,
> taken under the same conditions as the real picture, has the same long
> exposure noise as the real picture. It's then a simple mathematical
> process to use the dark frame to remove the noise from the picture using
> subtraction.
>
> --
> Jeremy | (E-Mail Removed)



 
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