Hi
tried out some lucky imaging with a 250f4 Newtonian and an ASI1600 camera operating on a 2mpix ROI. the seeing was fairly poor with normal 1 minute subs coming out at over 3 arcsec FWHM - the guiding was running at 1.3arcsec RMS, which is usually only marginally suitable for getting colour data. And a 3/4 moon was up.
The Saturn nebula is quite bright and I used 4 second x16bit subs for both lum and RGB. used SharpCap to collect the data - it has almost no time overheads. Selected luminance subs by hand and kept 498/~1000, based on image sharpness. The stack of selected subs came in at better than 2 arcsec FWHM, which was astounding based on the poor seeing - lucky imaging can certainly do the job on bright objects.
processing was interesting - after stacking, the only noise left was minor fixed patterns in the bias. With lots of short subs, the bias noise is more important than either the dark current or the shot noise in the background.
Attached image is a crop and rescaled 1.5x to around 0.5 arcsec pixel scale. Next step is to try it out with a Barlow - there is clearly a bit more resolution available with lucky imaging and it provides something to do if the moon is bright. Thanks for looking, Ray
Interesting. I would have expected "lucky imaging" to be even shorter subs, as in poor seeing even 4s subs would show some wobble.
You mention the 1min subs had 3arcsec FWHM, but compared that to the stacked 4s subs' < 2arcsec FWHM. Curious about a comparison of straight up sub vs sub, or stack vs stack - would assume that 1min subs stacked would give better FWHM than individual 1min subs as well?
That's turned out really nice Ray! What was your gain setting for this?
Thanks Colin. I use 100 for everything to date - seems to be useful for most purposes.
Quote:
Originally Posted by Paul Haese
4 second singles - interesting result and it has quite nice detail.
thanks Paul - just a start and an attempt to see what could be done in this intermediate timescale region.
Quote:
Originally Posted by multiweb
Great colors and details for such a tiny object. Well done.
thanks Marc!
Quote:
Originally Posted by troypiggo
Interesting. I would have expected "lucky imaging" to be even shorter subs, as in poor seeing even 4s subs would show some wobble.
You mention the 1min subs had 3arcsec FWHM, but compared that to the stacked 4s subs' < 2arcsec FWHM. Curious about a comparison of straight up sub vs sub, or stack vs stack - would assume that 1min subs stacked would give better FWHM than individual 1min subs as well?
Hi Troy. yes, maybe it should be called "mildly fortuitous" imaging or some such to distinguish from the planetary approach. Nonetheless, the results show that the same methods are applicable at these times.
I hadn't intended a direct comparison - just wanted to point out that conditions were marginal for normal imaging, but still produced quite good results with high speed imaging (actually I had decided that conditions were so bad that I would pack it in - only switched over to this target on a whim). I didn't take enough 1 minute images to be able to stack them - there wasn't any point.
Quote:
Originally Posted by gregbradley
Another good image Ray.
Short exposures definitely are showing their advantages. I think stars also look better in short exposures.
Greg.
thanks Greg. The stars probably look different because they are all dimmer than the nebula - no chance of saturating.
Quote:
Originally Posted by RickS
Looks good, Ray. Will have to compare with my "conventional" version when I get home.
Cheers,
Rick.
Be very interested to see Rick - I was thrilled to get anything at all on this beautiful object, but am sure that better results are possible with a bigger aperture and better seeing.
Quote:
Originally Posted by strongmanmike
Excellent details visible for such a small target Razzor Was this at the native prime focus of the 10" F4?
Mike
Thanks Mike - it turned out better than I had hoped. This was at normal focus of the 10 inch f4. I tried super-res processing, but could not improve on the result from simple scaling. No dither used - at 4 seconds, it slows things down too much. Need a way to dither every 10 subs maybe rather than every one.
Quote:
Originally Posted by Placidus
Superb, Ray. Adventurous and successful.
Very generous M&T. It was pleasing to get an image of this object under the conditions, but now I might have to look at getting a bigger scope
...
Hi Troy. yes, maybe it should be called "mildly fortuitous" imaging or some such to distinguish from the planetary approach. Nonetheless, the results show that the same methods are applicable at these times.
I hadn't intended a direct comparison - just wanted to point out that conditions were marginal for normal imaging, but still produced quite good results with high speed imaging (actually I had decided that conditions were so bad that I would pack it in - only switched over to this target on a whim). I didn't take enough 1 minute images to be able to stack them - there wasn't any point.
...
Cheers for the response. Be interesting to see future results.
Hi
tried out some lucky imaging with a 250f4 Newtonian and an ASI1600 camera operating on a 2mpix ROI. the seeing was fairly poor with normal 1 minute subs coming out at over 3 arcsec FWHM - the guiding was running at 1.3arcsec RMS, which is usually only marginally suitable for getting colour data. And a 3/4 moon was up.
The Saturn nebula is quite bright and I used 4 second x16bit subs for both lum and RGB. used SharpCap to collect the data - it has almost no time overheads. Selected luminance subs by hand and kept 498/~1000, based on image sharpness. The stack of selected subs came in at better than 2 arcsec FWHM, which was astounding based on the poor seeing - lucky imaging can certainly do the job on bright objects.
processing was interesting - after stacking, the only noise left was minor fixed patterns in the bias. With lots of short subs, the bias noise is more important than either the dark current or the shot noise in the background.
Attached image is a crop and rescaled 1.5x to around 0.5 arcsec pixel scale. Next step is to try it out with a Barlow - there is clearly a bit more resolution available with lucky imaging and it provides something to do if the moon is bright. Thanks for looking, Ray
Good detail Ray....1 second subs amazing!....how did you deal with the pattern noise?did the bias frames do the trick?
thanks Rob. Thought of suggesting Slightly Fortuitous Astro-imaging, but decided against it.
Quote:
Originally Posted by atalas
Good detail Ray....1 second subs amazing!....how did you deal with the pattern noise?did the bias frames do the trick?
Hi Louie. have not yet tried 1 second subs yet, but it is possible with bright targets. The bias noise was not too bad and I used masked low pass filtering to subdue it - in future will have to take a new bias set when doing ROI imaging - it should allow more effective removal of the residual noise.
Quote:
Originally Posted by RickS
You definitely have the edge on detail. My image was taken in the distant past with a GSO RC10 and SX-H18 (KAF-8300).
Cheers,
Rick.
Thanks for that Rick. It is a darned small object and 0.5 arcsec sampling is getting into the realm of the limiting resolution of a 10 inch scope. However, looking at what happens with planetary imaging, there should still be some gain in detail out to about f20, so there is still way to go before all hope of extra detail is lost. will be an interesting experiment to try it with a 2x Barlow - might not be fruitful, but interesting.
That's really good Ray, excellent details and a technique worth exploring to the max. It would be something to see what you could achieve on a night of better seeing and perhaps with the barlow - would it make the difference given the longer subs, not sure?
MF imaging indeed! - might turn up safer search results than Mil-F imaging
That's really good Ray, excellent details and a technique worth exploring to the max. It would be something to see what you could achieve on a night of better seeing and perhaps with the barlow - would it make the difference given the longer subs, not sure?
MF imaging indeed! - might turn up safer search results than Mil-F imaging
thanks Andy. The bright bits still had a lot of signal, so I may be able to stick with 4 seconds even with a Barlow if I wind the gain up - going to be balancing act, but this camera has a bit up its sleeve at gain 100, so there may still be some better resolution available by pushing a bit further.
yep, acronyms can lead one into some pretty iffy places on the www - maybe will stick to DSO lucky imaging.
