Q about very long exposures

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

 

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

 

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

 

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

 

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.

 

Is there any chance that light entered the eyepiece?

 

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

 

google up "amplifier glow"