Q about very long exposures

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Toby - 28 Nov 2006 09:17 GMT

I have a D200 which works fine in "normal" circumstances. However I tried to
do a long night exposure--about 3 minutes--and found that the top sides and
bottom middle of the frame were "washed out" with pink flare--looking almost
like light-struck film. Further tests showed that this was always in the
same place, appearing at about 1 minute exposure, and growing in strength
and size as the exposure time increased.

Is this normal? I have seen digital pix done with very long exposures that
looked fine. I'm running to the end of my warranty--should this be brought
back to Nikon?

TIA for any advice,

Toby

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David J Taylor - 28 Nov 2006 10:03 GMT

> I have a D200 which works fine in "normal" circumstances. However I
> tried to do a long night exposure--about 3 minutes--and found that
[quoted text clipped - 10 lines]
>
> Toby

Did you enable the dark frame subtraction? Effects at the edges are, I
understand, to the sensor becoming warm and the dark current increasing.
Dark frame subtraction may reduce the effect of the abnormally high dark
current, although it doubles the exposure time, presumably making the
sensor even warmer....

David

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Pete D - 28 Nov 2006 10:03 GMT

>I have a D200 which works fine in "normal" circumstances. However I tried
>to do a long night exposure--about 3 minutes--and found that the top sides
[quoted text clipped - 10 lines]
>
> Toby

Does the D200 do dark frame subtraction noise reduction, if so then turn it
on and try again.

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Pete D - 28 Nov 2006 10:04 GMT

http://www.kenrockwell.com/nikon/d200/d200-dark.htm

>I have a D200 which works fine in "normal" circumstances. However I tried
>to do a long night exposure--about 3 minutes--and found that the top sides
[quoted text clipped - 10 lines]
>
> Toby

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achilleaslazarides@yahoo.co.uk - 28 Nov 2006 12:15 GMT

> I have a D200 which works fine in "normal" circumstances. However I tried to
> do a long night exposure--about 3 minutes--and found that the top sides and
[quoted text clipped - 10 lines]
>
> Toby

At what ISO? If it does this at ISO 100, it's strange. Mine only starts
showing some of this around 10-15min at ISO 100. With dark frame
subtraction, I have exposures at several minutes at ISO 800 which do
not show this problem. In short, switch on DFS (ie "Long exp NR") to
get rid of this. You do pay a price in time, though.

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Charles Schuler - 28 Nov 2006 21:33 GMT

>I have a D200 which works fine in "normal" circumstances. However I tried
>to do a long night exposure--about 3 minutes--and found that the top sides
>and bottom middle of the frame were "washed out" with pink flare--looking
>almost like light-struck film. Further tests showed that this was always in
>the same place, appearing at about 1 minute exposure, and growing in
>strength and size as the exposure time increased.

Is there any chance that light entered the eyepiece?

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Toby - 29 Nov 2006 13:14 GMT

You have answered my question. I was exposing at ISO 1600, so I imagine that
it is quite normal for the "purple haze" to appear after 3 mins at that high
setting. Many thanks to all for taking the time to enlighten me.

Cheers,

Toby

>>I have a D200 which works fine in "normal" circumstances. However I tried
>>to do a long night exposure--about 3 minutes--and found that the top sides
[quoted text clipped - 4 lines]
>
> Is there any chance that light entered the eyepiece?

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eawckyegcy@yahoo.com - 29 Nov 2006 18:24 GMT

> I have a D200 which works fine in "normal" circumstances. However I tried to
> do a long night exposure--about 3 minutes--and found that the top sides and
> bottom middle of the frame were "washed out" with pink flare--looking almost
> like light-struck film. Further tests showed that this was always in the
> same place, appearing at about 1 minute exposure, and growing in strength
> and size as the exposure time increased.

google up "amplifier glow"

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