From: Milton Aupperle <milton@outcastsoft.com>
Date: June 15, 2006 2:47:09 PM MDT
To: Astro_IIDC@yahoogroups.com
Subject: Re: [Astro_IIDC] Monochrome Unibrain results
Hi Alan;
On 15-Jun-06, at 1:48 PM, Alan Friedman wrote:
Hi Milton -
A good summary.
Thanks..
I recently spent a night imaging Jupiter with my 6" scope - something I had not done in many years. I chose a focal length of about 3 meters (next time I would increase this slightly) which gave similar exposures values to my 10" at 7 meters - my normal set-up for Jupiter. I was surprised how much detail was recorded and how well the image handled being upscaled in Photoshop. When I finished combining the RGB I will share it with the group.
Great - can't wait to see them. It's been raining here for 2+ weeks now so I've gotten no imaging at all. The Lightning storms over the past two nights have been phenomenal. You can read by the lightning at night as we were getting that many strikes per minute.
I also found that selection, alignment and stacking in AstroIIDC at this image scale (I used the planetary mode for stacking) was much more dependable than at the larger image scale I usually use. This is probably due to smoother signal, higher contrast features and reduced movement from atmospheric distortion in the individual frames at the shorter focal length. It is really a pleasure to let Astro IIDC do all the work.
Then you probably need to reduce the pixel matching tolerance when using the longer focal length, especially with average / mediocre seeing and high gains.
Also using a larger pixel area does not always work as well as smaller area for matching on features. This is especially true for low contrast images with high gains, because you wind up matching the background gain noise rather than feature of interest. So it's better to use say a 32x32 or 64x64 pixel area and partially contain a "feature" a larger area with flat noisy data. However what constitutes low contrast is debatable. All my Mars image raw frame looked like this:
http://groups.yahoo.com/group/Astro_IIDC/files/Other/Mars Single Frame.jpg
and there is very little contrast in them for aligning with (background has values of 3 to 5 out of 256, disk brightest core is 70 out of 256). I chose to keep them dark with lower Brightness / Gains rather than brighten it up using higher noisy gains. I found that I lost a lot of subtle image detail with high gains on the Flea Camera and now will not go over 500 out of 1023 (around 40 - 50%) of the Brightness ever again.
And after it's all smoothed out, you can brighten it post capture like this.
http://groups.yahoo.com/group/Astro_IIDC/files/Other/Mars Enhanced.jpg
I never really realized it, but that image has a resolution of around 0.5 arc seconds, which is twice the theoretical resolving power of my MAK 5.1" aperture scope . The disk is 74 pixels tall and at that time Mars was 20 arc seconds, so each pixel represents 0.27 arc seconds.
I will be interested to see if detail is recorded on Ganymede at the shorter focal length. Capturing this and certain other features (such as recording the location of the Encke division on saturn) have seemed to need a long focal length - but maybe not...
That will definitely be interesting to see.
Rod Kennedy (Australia) caught some detail on Ganymede
http://homepage.mac.com/astrod/Sites/gallery/images/rodJupiter.jpg
using LX200 10" and a ToucCam.
TTYL..
Milton J. Aupperle
President
ASC - Aupperle Services and Contracting
Mac Software (Drivers, Components and Application) Specialist
#1005 - 815 14th Avenue. S.W.
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