From: Alan Friedman <alan@greatarrow.com>
Date: April 20, 2005 1:30:17 PM MDT
To: Astro_IIDC@yahoogroups.com
Subject: Re: [Astro_IIDC] Jupiter Sharpness Comparison
On Apr 20, 2005, at 2:51 PM, Milton Aupperle wrote:
Hi Alan;
It's not a huge difference and sharpening will always increase noise
levels. The key with my technique is to reduce noise on the CCD side by
keeping the Brightness/Gains as low as possible. At high gains subtle
detail gets lost in the noise and then all sharpening will do is
amplify the noise.
It's a night to night toss up. The detail can also be sacrificed in the longer exposures required for low gain imaging.
Also sharp focus is a hugely important issue too. I have a few movies I
took before this one (using the moon for focusing) that weren't quite
as sharp and the white spots to the upper left of the red spot are
basically gone in those images.
Definitely true - and a killer on nights of poor seeing or with a moving mirror system. I added an auxiliary crayford focuser to my 10" mak which has helped a great deal.
It's hard to say exactly without more information, for example the
method (Planetary or Lunar/Solar) used and what CI % you used for the
sharpness selector. Also a sample of the images used as source would be
helpful too. Some of my lunar images at really long focal lengths (5+
meters) were drifting 70 to 100 pixels by the time 1000 frames had
been collected and they aligned fine.
Interesting. I was poorly polar aligned the other night and with the long exposures through my red filter the planets drifted much of the way across the chip.
Also the Planetary/Lunar option is a bit misleading. Planetary works
good for smaller disk sizes, but since your Saturn images are really
large, you probably would be better off using Lunar/Solar which aligns
using an edge detection method rather than the simple planetary
centroid method.
The other possibility could be that the "pixel align" finnish is
getting tripped up because the disk of saturn is basically featureless
(at least for a 32x32 pixel comparsion block) and with high gain /
noise levels it may be thinking the noise it's seeing is "features". If
it does not see any "significant" variance in the images it disables
this fine tuning automagically, but I may have to add an option to turn
it off manually for these cases.
Hope That helps..
Very helpful, thanks.
I can't help but think that the ability to select an area for alignment will be critical to achieving good results. For saturn images I always align the stack three times (disk, and each ansae) and sometimes include a separate alignment on the polar region and forward crepe ring too. In all but the finest seeing (and who's got that) most frames are bloated in some area changing the shape of the planet in each frame. My process involves some mosaic techniques in Photoshop afterwards to combine the stacks. It is too much work for mediocre nights, but the results will support the extra work when the conditions are above average.
Alan
Milton J. Aupperle
President
ASC - Aupperle Services and Contracting
Mac Software (Drivers, Components and Application) Specialist
#1005 - 815 14th Avenue. S.W.
Calgary Alberta Canada T2R0N5
1-(403)-229-9456
milton@outcastsoft.com
www.outcastsoft.com
Alan
On Apr 20, 2005, at 1:44 PM, milton_aupperle wrote:
Hi folks;
I had very good stable skies last night as the jet stream shifted
way
north of me into the North West Territories and Arctic. So I managed
to get some good shots of Jupiter (with GSR) and Luna last night -
accumulating another 9 gigabytes of 16 bit video movies.
Since I finally had some decent shots of Jupiter to work with, I ran
the same movie through Astro IIDC for stacking and alignment, and
then
varied the pre sharpness amount in each run from none to extreme.
Astro IIDC has the ability to sharpen each frame before stacking and
aligning them - which in theory should help accentuate subtle
features
as long as the CCD gain noise isn't too high.
You can read about it and see the (subtle) difference that it makes
in
the Jup_Comp_050419.jpg file in the Planetary folder. The 16 bit tiff
is a little bit easier to see the subtle differences too.
One thing I'm now more convinced of now is that 16 bit planetary
imaging does make a difference for very subtle features. However to
take advantage of it you need very good seeing conditions (and have
to
stay in 16 processing from start to finnish) - otherwise
it may not be worth the money.
TTYL..
Milton J. Aupperle
President
ASC - Aupperle Services and Contracting
Mac Software (Drivers, Components and Application) Specialist
#1005 - 815 14th Avenue. S.W.
Calgary Alberta Canada T2R0N5
1-(403)-229-9456
milton@outcastsoft.com
www.outcastsoft.com
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