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Hi troops,

i have just taken some star trail pictures and upon examination, have
noticed some pixels are unusually bright dont really belong in the image.

I have heard about hot and dead pixels but dont know exactly what to look
for.

could someone take a look at these 2 images and let me know what the hell is
going on here!!!

http://www.marknowak.co.uk/images/pixel-1.jpg (17Kb)
http://www.marknowak.co.uk/images/pixel-2.jpg (65Kb)


There are a number of image 1 and 2 of image 2 in all of the images i have
taken this evening. I have only noticed these when taking star trail pics,
and so does not really affect the other types of photography i do


Thanks for any help, Mark

"Mark N" <> wrote in message
newsJ_Sa.2503$...
> Hi troops,
>
> i have just taken some star trail pictures and upon examination, have
> noticed some pixels are unusually bright dont really belong in the image.
>
> I have heard about hot and dead pixels but dont know exactly what to look
> for.
>
> could someone take a look at these 2 images and let me know what the hell
is
> going on here!!!
>
> http://www.marknowak.co.uk/images/pixel-1.jpg (17Kb)
> http://www.marknowak.co.uk/images/pixel-2.jpg (65Kb)

Oh no!
Yet another Mark!
You've zoomed in on the image so much that it's hard to say.
Post a simple full-res crop to give us a better idea.

ok, i have posted a better image. its a 66% zoom into the image.

http://www.marknowak.co.uk/images/pixel-3.jpg (59Kb)


I have downloaded a small utility called deadpixeltest

http://www.starzen.com/imaging/deadpixeltest.htm

from this i realise that i have no dead pixels (phew) and seem to get more
hot pixels the longer the exposure. I did a 30 second exposure test with
this and it found no hot pixels until i dropped the threshold down to about
30

The longer the exposure, the more hot pixels. So i dont think that there is
too much to worry about. Ahh, i can finally sit back, relax, and think about
going to bed rather than staying up all night and trying to fix something
that is not broken!!!


Cheers




"Mark M" <> wrote in message
news:g8%Sa.13180$Bp2.335@fed1read07...
>
> "Mark N" <> wrote in message
> newsJ_Sa.2503$...
> > Hi troops,
> >
> > i have just taken some star trail pictures and upon examination, have
> > noticed some pixels are unusually bright dont really belong in the
image.
> >
> > I have heard about hot and dead pixels but dont know exactly what to
look
> > for.
> >
> > could someone take a look at these 2 images and let me know what the
hell
> is
> > going on here!!!
> >
> > http://www.marknowak.co.uk/images/pixel-1.jpg (17Kb)
> > http://www.marknowak.co.uk/images/pixel-2.jpg (65Kb)
>
> Oh no!
> Yet another Mark!
> You've zoomed in on the image so much that it's hard to say.
> Post a simple full-res crop to give us a better idea.
>
>

presuming these are images of stars moving across the frame, what celestial
body would have been stationary?

Looks like a ccd issue to me. check the scale in Photoshop or similar and
see if it is maxed out. ccd thermal noise (exposure dependant) should be
"random", however, tests of exposure noise in my 5700 were repeatable. I
actually had several hot pixels and the camera is in the shop for repair.

good luck,

rma



"Mark N" <> wrote in message
news:Ww%Sa.2526$...
> ok, i have posted a better image. its a 66% zoom into the image.
>
> http://www.marknowak.co.uk/images/pixel-3.jpg (59Kb)
>
>
> I have downloaded a small utility called deadpixeltest
>
> http://www.starzen.com/imaging/deadpixeltest.htm
>
> from this i realise that i have no dead pixels (phew) and seem to get more
> hot pixels the longer the exposure. I did a 30 second exposure test with
> this and it found no hot pixels until i dropped the threshold down to
about
> 30
>
> The longer the exposure, the more hot pixels. So i dont think that there
is
> too much to worry about. Ahh, i can finally sit back, relax, and think
about
> going to bed rather than staying up all night and trying to fix something
> that is not broken!!!
>
>
> Cheers
>
>
>
>
> "Mark M" <> wrote in message
> news:g8%Sa.13180$Bp2.335@fed1read07...
> >
> > "Mark N" <> wrote in message
> > newsJ_Sa.2503$...
> > > Hi troops,
> > >
> > > i have just taken some star trail pictures and upon examination, have
> > > noticed some pixels are unusually bright dont really belong in the
> image.
> > >
> > > I have heard about hot and dead pixels but dont know exactly what to
> look
> > > for.
> > >
> > > could someone take a look at these 2 images and let me know what the
> hell
> > is
> > > going on here!!!
> > >
> > > http://www.marknowak.co.uk/images/pixel-1.jpg (17Kb)
> > > http://www.marknowak.co.uk/images/pixel-2.jpg (65Kb)
> >
> > Oh no!
> > Yet another Mark!
> > You've zoomed in on the image so much that it's hard to say.
> > Post a simple full-res crop to give us a better idea.
> >
> >
>
>

"ralford" <> wrote in message
news:vj0Ta.82781$.. .
> presuming these are images of stars moving across the frame, what
celestial
> body would have been stationary?

You're kidding, right?

"Mark N" <> wrote in message
news:Ww%Sa.2526$...
> ok, i have posted a better image. its a 66% zoom into the image.
>
> http://www.marknowak.co.uk/images/pixel-3.jpg (59Kb)
>
>
> I have downloaded a small utility called deadpixeltest
>
> http://www.starzen.com/imaging/deadpixeltest.htm
>
> from this i realise that i have no dead pixels (phew) and seem to get more
> hot pixels the longer the exposure. I did a 30 second exposure test with
> this and it found no hot pixels until i dropped the threshold down to
about
> 30
>
> The longer the exposure, the more hot pixels. So i dont think that there
is
> too much to worry about. Ahh, i can finally sit back, relax, and think
about
> going to bed rather than staying up all night and trying to fix something
> that is not broken!!!

I agree that nothing is broken.
Actually, it's a pretty decent performance for a digital camera to only
exhibit that one major flaw in long exposure.

Mark N wrote:

> from this i realise that i have no dead pixels (phew) and seem to get more
> hot pixels the longer the exposure. I did a 30 second exposure test with
> this and it found no hot pixels until i dropped the threshold down to about
> 30
>
> The longer the exposure, the more hot pixels. So i dont think that there is
> too much to worry about. Ahh, i can finally sit back, relax, and think about
> going to bed rather than staying up all night and trying to fix something
> that is not broken!!!

I can't see your images tonight Your server must be down.

Yes.. On the 10D, the longer the exposure, the more 'hot' pixels show up.

I've found the acceptable limit is around 3 minutes.. Anything more, and you
get lots of speckles..

Below is a 600 second (10 minute) exposure I did last month. The speckles in
the sky aren't stars.. (If they were, they'd be streaks). There are a couple
of airplane light trails crossing the sky. The image is exactly as it came
from the camera.. I copied it from the camera to my computer, then I copied it
directly to pbase.com.

(Caution this is a 2.5 meg download)

http://www.pbase.com/image/19296218/original

If you remove the '/original' from the end of the above URL, you'll see a
smaller version of the image, but the speckles don't show up well on the
resized versions.

Indeed, i was actually very impressed with how low the noise is even with
exposures as high as 5 minutes, there simply wasn't any significant noise
(ISO set to 100).

I live in a city and so 5 minutes is really the max exposure length - i
found - before the image would be washed out by street lighting. But next
time i go away somewhere remote id love to try 1 hour or more exposures

Mark



> I agree that nothing is broken.
> Actually, it's a pretty decent performance for a digital camera to only
> exhibit that one major flaw in long exposure.
>
>

"ralford" <> wrote in message
newst9Ta.86160$.. .
> not kidding at all. Polaris would appear stationary in a time exposure,
> however, the star tracks would have it as their center of radius.
>
> now, I've not time to muck about with who is moving - actually any
reference
> frame is possible, however, some certainly lead to model simplifications.
> in this case I choose to think of the camera as stationary.
>
> you must be confused, right?

How can it appear stationary in the frame with the rotation of the Earth
causing perceived movement?

In message <PJ_Sa.2503$>, Mark N
<> writes
>Hi troops,
>
>i have just taken some star trail pictures and upon examination, have
>noticed some pixels are unusually bright dont really belong in the image.
>
>I have heard about hot and dead pixels but dont know exactly what to look
>for.
>
>could someone take a look at these 2 images and let me know what the hell is
>going on here!!!
>
>http://www.marknowak.co.uk/images/pixel-1.jpg (17Kb)
>http://www.marknowak.co.uk/images/pixel-2.jpg (65Kb)
>
>
>There are a number of image 1 and 2 of image 2 in all of the images i have
>taken this evening. I have only noticed these when taking star trail pics,
>and so does not really affect the other types of photography i do
>
>
>Thanks for any help, Mark
>
>

Just take some long exposures with the lens cap on, then you'll know
they are not heavenly bodies!
--
Alan F Cross