Quote:
Originally Posted by ericwbenson
Hi Ray,
Nice graphs, well done. One thing not quite captured here, and I don't know how one would do it in a completely analytical way, is the fact that when we dither our images the FPN (I'll just call it that for now) is smeared when the stacking actually occurs. Does it make it worse or better, not sure, haven't thought that far. But I do know that it would be better if wasn't there to start with!
Point two: Many years ago I was shooting the breeze with Paul Boltwood and Doug George at Doug's place. Paul had just recently won the deep sky competition set out by Sky and Tel mag (amateurs imaging the Hubble deep field to see how deep they could go), and was quite surprised that he had beat others, since he imaged from an obs attached to his house, in suburbia (Kanata) of a ~750K population center (Ottawa). He had only a 16" newtonian reflector and a camera he had made himself (this guy was very bright and handy, I can't imaging designing and building a custom CCD holder myself!). One thing he said was: going deep without really really really good flats, fogget about it...flats ultimately are THE limiting factor in how deep you can go.
Best,
EB
PS. I just found a link to short bio on him:
http://astro-canada.ca/_en/a2223.php |
Thanks very much for the info Eric.
I was also concerned about what happens when you dither. I think that it just randomises the fixed pattern noise and turns it into random noise like that from other sources - the noise power is the same, but the spatial distribution is no longer consistent with ref to the star pattern. That was the basis for the graphs - assuming random noise for the FPN made it easy to quadrature combine noise from different sources.
If you want to get as deep as possible, removing any manageable noise sources makes sense, so quality flats are essential. However, if your system has low non-uniformity, concentrating on lights and neglecting flats may be a perfectly sensible approach for many targets.
I was surprised at how much difference flats can make with some cameras.
regards ray
edit: that's an interesting site.