007f01c17d0d$9c4fb200$5b57443f ^a^ bberger">
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^ earthlink dawt net>
To: "George Roberts" <gr ^a^ pobox dot com>
Cc: "ATMOB Discussion List" <atmob-discuss ^a^ 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^ Earthlink dawt net
mcarnes ^a^ Lexicon dot com
<http://home.earthlink dawt net/~moogiebird/mc>
From: "George Roberts" <gr ^a^ pobox dot com>
Date: Tue, 4 Dec 2001 14:23:14 -0500
To: "Mario E. Motta" <mmotta ^a^ massmed daht org>
Cc: "Bruce Berger" <berger ^a^ mediaone dawt net>, "Daniel Feldkhun"
<delf ^a^ MIT.EDU>,
"Lew Gramer" <dedalus ^a^ latrade dot com>, "Michael Carnes"
<moogiebird ^a^ earthlink dawt net>, "ATMOB Discussion List"
<atmob-discuss ^a^ 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^ pobox dot com
http://www.pobox dot com/~gr