Dark Frames

I have been experimenting with registax and my toucam.

I stacked a couple of thousand frames of M42 (through open window) and there
does indeed seem to be some nebula showing. I would like some advice on
these shots as there are several lines running down them. Any idea what this
is? I thought it might be noise but it seems a bit excesive. I will upload
them somewhere once I find a suitable place.

Anyhoo, I then read about Dark Frames, so I made one using about 200 frames
stacked. When I used this in Registax it deleted most of the detail in the
shot so I was only left with two or three stars (greatly dimmed)and no
nebula. I have thought about this and have come to the following conclusion
and would like advice as to where I am wrong:

Registax applies my dark frame to each frame individually (rather than the
finished stack) so I should probably be using a dark frame which is made of
either one frame or a small number. What is the best number? Or am I
completely wrong?
Also, when making the dark frame, is it important to have the camera
settings the same as when capturing the image of the star etc?

Regards,

Stuart

Ive just noticed that setting the fps higher gets rid of the vertical lines.

"Stuart M" wrote in message
...
I have been experimenting with registax and my toucam.

I stacked a couple of thousand frames of M42 (through open window) and
there
does indeed seem to be some nebula showing. I would like some advice on
these shots as there are several lines running down them. Any idea what
this
is? I thought it might be noise but it seems a bit excesive. I will
upload
them somewhere once I find a suitable place.

Anyhoo, I then read about Dark Frames, so I made one using about 200
frames
stacked. When I used this in Registax it deleted most of the detail in the
shot so I was only left with two or three stars (greatly dimmed)and no
nebula. I have thought about this and have come to the following
conclusion
and would like advice as to where I am wrong:

Registax applies my dark frame to each frame individually (rather than the
finished stack) so I should probably be using a dark frame which is made
of
either one frame or a small number. What is the best number? Or am I
completely wrong?
Also, when making the dark frame, is it important to have the camera
settings the same as when capturing the image of the star etc?


Hi Stuart,

What you did should have worked out ok. Yes you should use exactly the same
setting for the dark and stack them to get a good average, then save it as a
bmp. Perhaps the nebula was still there but much darker with the background
noise subtracted. Did you try stretching the result? (brightness contrast
and gamma settings) Do this in registax before you save it as a bmp.

Not sure about the lines at low frame rates. Low fps are normally better as
there is less compression over USB

BTW to avoid this turning into an image processing session which is probably
OT here, It might be better to move to the QCUIAG yahoo group

Robin

"

Hi Stuart,

What you did should have worked out ok. Yes you should use exactly the
same
setting for the dark and stack them to get a good average, then save it as
a
bmp. Perhaps the nebula was still there but much darker with the
background
noise subtracted. Did you try stretching the result? (brightness contrast
and gamma settings) Do this in registax before you save it as a bmp.

Not sure about the lines at low frame rates. Low fps are normally better
as
there is less compression over USB

BTW to avoid this turning into an image processing session which is
probably
OT here, It might be better to move to the QCUIAG yahoo group

Robin



Robin,

I think the problem is that I didnt take a dark frame at the same time so
the settings are probably all different. It was only when I got such a bad
result that I thought about it.

Perhaps you are right about this straying off topic and into the realms of
image processing. I will take your advice and join the yahoo group.

Thanks again.

Stuart

You may like to join the UKAstroImaging forum at
http://ukastroimaging.co.uk/forums/

There should be someone there who has had the same experiences as you & can
give advice.

Dave
------------------------------------------------------
David Warrington BSc
North Essex Astronomical Society
http://www.neas.org.uk
------------------------------------------------------


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hello David,

I have found my answer but thanks for the link.

Regards

Stuart


"David Warrington" wrote in message
...
You may like to join the UKAstroImaging forum at
http://ukastroimaging.co.uk/forums/

There should be someone there who has had the same experiences as you &
can
give advice.

Dave
------------------------------------------------------
David Warrington BSc
North Essex Astronomical Society
http://www.neas.org.uk
------------------------------------------------------


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