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

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

I'll get my Minolta DiMAGE 5 3.34 megapixel next week sometime, and will try
the same thing. I think I can expose up to 30 seconds. It should be
interesting.....

Bruce
----- Original Message -----
From: "George Roberts" <gr*at*pobox dot com>
To: "Mario E. Motta" <mmotta*at*massmed daht org>
Cc: "Bruce Berger" <berger*at*mediaone dawt net>; "Daniel Feldkhun" <delf*at*MIT.EDU>;
"Lew Gramer" <dedalus*at*latrade dot com>; "Michael Carnes"
<moogiebird*at*earthlink dawt net>; "ATMOB Discussion List"
<atmob-discuss*at*atmob daht org>
Sent: Tuesday, December 04, 2001 2:23 PM
Subject: 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*at*pobox dot com
> http://www.pobox dot com/~gr
>
>
>
References: