[Prev][Next][Index][Thread]
(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
Follow-Ups:
References: