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

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: