From: Alan Friedman <alan@greatarrow.com>

Date: November 23, 2005 10:08:34 AM MST

To: Astro_IIDC@yahoogroups.com

Subject: Re: [Astro_IIDC] Re: solar mosaic

Hi Steve -

The advantage gained by using multiple alignment points is directly related to the seeing. In perfect conditions it would have no advantage because the frame would not undulate at all. (If I ever experienced this the first thing I would do is check for a pulse). Depending on the amount and character of the seeing undulations and on the amount of the frame the image takes up - aligning the stack on multiple points can be very helpful.

Another related factor is the focal length of the set-up. The higher the magnification the more pronounced the undulations. My high resolution image from Sunday was taken at f22 and the deformations produced too soft an image for my taste when stacked in AstroIIDC. The mosaic was shot at prime focus of my 5" (with 90mm filter in front - f11) - here the deformations were much more subtle and AstroIIDC did a fine job of stacking the images - which is a good thing because I needed 9 images for the mosaic. With AstroIIDC used for stacking the entire image was processed and assembled while watching Alfred Hitchcock"s Suspicion on TCM - about two hours, I guess.

I also like the Laplacian tool in KIS - but I usually only use it if I am hand selecting and stacking the frames in this program. For the mosaic, I opened the 16 bit images stacked in AstroIIDC in Photoshop CS2. I had selected approximately the same number of frames for each stack so applying the same unsharp mask to all images created a set of images with almost identical values. My preference is to use as small a pixel radius as possible for unsharp masking - especially for solar and lunar images. It is very easy to create too much contrast - I prefer to show a more natural looking aspect. I believe a setting of 1.2 pixel diameter was what I used for the mosaic images.

best,

Alan

On Nov 22, 2005, at 10:15 PM, Steve Bryson wrote:

Hi Alan - I've been looking at past posts and I'm beginning to understand how you

make such spectacular images. I'll try the multi-stacks with different alignment

regions trick soon on some of my images.

But did you do this trick on this great solar image? As far as I can tell I can't

specify a region for alignment when stacking with Astro IIDC. Was the solar image

a mosaic of simple stacks from Astro IIDC? It's hard to believe you got such

uniform detail with normal stacking.

Also, what kind of sharpening did you use on this image? I'm partial to

Laplace Pyramid sharpening in Keith's Image Stacker.

Best

Steve

--- In Astro_IIDC@yahoogroups.com, "Alan Friedman" <alan@g...> wrote:

> Hi all -

> Here is a mosaic from a rare Buffalo sunny November Sunday.

> http://groups.yahoo.com/group/Astro_IIDC/files/Solar/ar822wide.jpg

> All the component frames were selected and stacked with Astro IIDC using the lunar/

solar

> setting and 65% CI. Image processing and assembly of mosaic was done in Photoshop

CS2.

> The sun was 25 degrees above the horizon when these streams were captured.

> best wishes -

> Alan