[Prev][Next][Index][Thread]

Re: (ATMoB:Discuss) astrophotography with ordinary digital cameras

Couldn't one just capture one dark frame at the start of shooting and use it
throughout the night? Or is it desirable to have the dark frame taken when
the CCD is close to the same temp as when the subject photo was taken?

Bruce Berger


----- Original Message -----
From: "Michael Carnes" <moogiebird a t earthlink dawt net>
To: "George Roberts" <gr a t pobox dot com>
Cc: "ATMOB Discussion List" <atmob-discuss a t atmob daht org>
Sent: Tuesday, December 04, 2001 3:20 PM
Subject: Re: (ATMoB:Discuss) astrophotography with ordinary digital cameras


> It would seem to me that it's important to save the image as a TIFF file.
> JPEG might remove some of the speckles you'd like to keep, either in the
> image or the black shot.
> --
> Michael Carnes
> 252 Washington Street
> Arlington, MA 02474
> moogiebird a t Earthlink dawt net
> mcarnes a t Lexicon dot com
> <http://home.earthlink dawt net/~moogiebird/mc>
>
> > From: "George Roberts" <gr a t pobox dot com>
> > Date: Tue, 4 Dec 2001 14:23:14 -0500
> > To: "Mario E. Motta" <mmotta a t massmed daht org>
> > Cc: "Bruce Berger" <berger a t mediaone dawt net>, "Daniel Feldkhun"
<delf a t MIT.EDU>,
> > "Lew Gramer" <dedalus a t latrade dot com>, "Michael Carnes"
> > <moogiebird a t earthlink dawt net>, "ATMOB Discussion List"
<atmob-discuss a t atmob daht org>
> > Subject: (ATMoB:Discuss) astrophotography with ordinary digital cameras
> >
> >> Interesting, ... this is the first report i have heard of anyone
actually
> >> trying dark
> >> subtracting on a small digital camera, and you say it works. Good idea.
> >
> > It works very well at removing about a hundred false stars (and some are
> > multipixel
> > stars that really look like stars), but there is another level of noise
> > involved that will
> > probably come into play as I approach 60 seconds.  The longest exposure
my
> > camera
> > does is 8 seconds and I didn't try taking 10 pictures because I don't
have the
> > software
> > to align them.
> >
> > As far as cooling the camera -- I did this in weather around 20 degrees
F
> > (note the
> > snow in the picture) and noticed that my photographs of my lens cap had
fewer
> > stars as the camera cooled so I had to take multiple pictures of the
lens cap
> > as
> > time went on.  If I had let the camera cool before I started taking
pictures I
> > presume
> > I would only need a single picture of the lens cap.
> >
> > After 8 seconds, I can see down to about mag 5 or 6, but that's it.
Can't see
> > the milky
> > way or anything like that.  Here.  I'll put some sample pictures up:
> >
> > All pictures are 8 second exposures and were taken at 1600 pixels but I
threw
> > half
> > the pixels away in each dimension to reduce the size of these pictures
(most
> > of the pixels
> > are black anyway!).  The camera is a Sony DSC-S50 2.1 Megapixel camera -
> > middle
> > of the line digital camera in today's market and costs about $500.  I
did no
> > tracking.
> > I used a tripod only and used the self timer to avoid jiggles (no cable
> > release).
> >
> > My house at night no modification to raw picture:
> > http://people.ne.mediaone dawt net/robertsg/pic1.jpg
> >
> > Same picture with lens cap photograph removed (subtracted a picture of
the
> > lens cap taken soon after)
> > http://people.ne.mediaone dawt net/robertsg/pic2.jpg
> >
> > Open the above two pictures in two different windows and maximize both
and
> > toggle between the windows
> > (hold down "alt" key, press "tab" key and *then* release "tab" key and
then
> > release "alt" key.  Do this
> > 30 times quickly).  Or do "back" and "forward" in web browser (hold down
"alt"
> > key, press left arrow,
> > then press right arrow, repeat 30 times quickly).
> >
> > Orion after subtraction
> > http://people.ne.mediaone dawt net/robertsg/pic3.jpg
> >
> > Hyades and Plieades after subtraction (zoomed in to about 20 degrees
field of
> > view)
> > http://people.ne.mediaone dawt net/robertsg/pic4.jpg
> >
> > Not real impressive pictures, but an impressive improvement over
> > non-subtracted images.
> > I suspect the ccd's that most astronomers use have much less noise than
my
> > camera (but
> > fewer pixels!).
> >
> > - George Roberts
> > mailto:gr a t pobox dot com
> > http://www.pobox dot com/~gr
> >
> >
>
>
Follow-Ups: References: