Re: [APML] Creating H-Alpha Color Composites

["Richard Crisp" <rdcrisp@earthlink.net>]

----- Original Message ----- 
From: "Jason Ware" <jtw@galaxyphoto.com>
> The only problem I have is that the Tech Pan images
> have bloated bright stars due to halation that I
> don't have on the color images. I guess this is not
> a problem with CCD.


actually halation is a problem with CCD and a good many filters.

i get terrible halation with my [SII] filter and also get it with Ha and 
[OIII] but to a lesser degree.

they look about like the halos in your image.

here's a typical example:
http://www.narrowbandimaging.com/ic1396_fsq6303_s2hao3_page.htm

here's another
http://www.narrowbandimaging.com/ic1848_fsq6303_s2hao3_page.htm

and another from a different imager (Russ Croman):
http://www.rc-astro.com/nebulae/nam_peli_map.htm

I've noticed similar haloes in Hubble shots such as this:
http://store1.yimg.com/I/skyimage_1813_0

I think it just goes with the territory, the filters just have internal 
reflections that can leave artifacts. It is particularly bad with [SII].

Normally I can work on them a bit with Photoshop and improve the situation 
but the raw data nearly always has them in my experience and observations.

rdc



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