thanks Rick,
On page 40 of the book you referenced to it has an example of the S/N ratio being the same for stacking via summing and then averaging. Both methods produce the same S/N ratio. But would the summed set have higher pixel values? (greater signal, but also greater noise, as it hasnt been divided by the number of sub frames taken). I know summing is not used because it has some artifact drawbacks in the final image but that s not my point.
The 10 min example you gave, would this be a sum or average, not for the purposes of S/N ratio, but for detecting faint objects. How can you not go deeper with a 10min exposure than 10 one min exposures. I guess the average of 10 one min exposures may show some faint detail.
thanks for the link
Josh
Quote:
Originally Posted by RickS
Not quite right, Josh, but it takes a while to grasp and it's not entirely intuitive.
You don't go any deeper with a 10 minute exposure than you do with a stack of 10 one minute exposures. The difference is that you will incur read noise once in the first example and ten times in the second. How big a difference this makes will depend on the characteristics of your camera.
I'd recommend reading a decent reference on the topic. Craig Stark has written some good articles. See the Signal to Noise series here: http://www.stark-labs.com/craig/articles/articles.html
The book The Handbook of Astronomical Image Processing is a very interesting and informative read too.
Cheers,
Rick. |