sub-frames

[rogerco]

Beginners question -

Why take multiple sub frames, why not just take one and duplicate it and then stack the copies ?

:screwy:

[dugnsuz]

Hi rogerco,
This doesn't work as the noise produced by the camera sensor is random and shows up at different places/intensities on each image.
By stacking individual shots you smooth out that noise over the background of the image and boost the signal (stars and other stuff!)

Hope I've explained it well enough - it's just the law!!!!;)
Cheers
Doug:thumbsup:

[Matty P]

I wish we could Roger, it would Astrophotgraphy soooo much easier but you need to record as much data as possible during an exposure. Recording faint objects in the night sky is all about the signal-to-noise ratio. Meaning that if you only record one sub frame and stack a couple of duplicates together the resulting image will have a very low signal-to-noise ratio.

The more Subs exposures the better. :thumbsup:

[rogerco]

Thanks, I have experimented. The results are different, "smoother" I think would be a non technical description, which I suppose is a nother way of saying noise. But the results are quiet reasonable. I am wondering if there is a half way point between the randomness of multiple exosures and duplicating. I can understand the randomness of noise resulting in noise registering on different pixels and thus smothing out. But I would have thought the overall S/N ration would be the same.

Needs more experiment
Roger