Re: [APML] Cederblad 214, NGC 7822

["Robert Gendler" <robgendler@worldnet.att.net>]

Loke,
The reason to blend the red and HA is to bring back the
normal distribution and size of stars into the luminance. The way
I did it (using a "lighten" blend in PS) preserves all the HA contrast
together with the stars of the red image. I then used this blend as the
red channel and then applied the HA/red again as luminance in PS.
As you correctly mentioned the blue channel is the toughest to achieve
decent focus with these nonapo lenses but a reasonably decent  focus can
be achieved if one is patient and persistent. In general its hard to focus
at F4
and CCD's are much more exquisitely revealing of imperfect focus than film
(especially the ST10 with 6.8um pixels). Part of the problem is also the
lack of
perfect field flatness with these lenses. I've learned to focus on a star
about 2/3
out from center (as opposed to center) to get decent focus across the chip.
Rob Gendler
Email: robgendler@att.net
Web site: http://www.robgendlerastropics.com/
----- Original Message -----
From: "lkt" <tan@cox.net>
To: <astro-photo@seds.org>
Sent: Sunday, September 01, 2002 4:54 PM
Subject: Re: [APML] Cederblad 214, NGC 7822


> Rob,
>
>  Very nice image and yes the stars are much tighter in this version.
> Interesting, so the blue halos were due to an out of focus blue channel?
> Do you think blending of HA and red actually made a difference in star
> sizes or is it just better blue focus? Thanks.
>
> Loke
>
>
>
>
> Robert Gendler wrote:
> >
> > Thanks Volker and Chris.
> > What I did differently with this one was to make a blend of the
> > HA data and red channel (using lighten) and then substitute this
> > for the red channel. In this way the stars are borrowed from the
> > red channel and the RGB is now strong enough to be matched
> > with the high contrast HA luminance. The problem on the previous
> > image I did (IC1396) was imperfect focus for the blue channel. I spent
> > more time on this image getting good focus so there are no blue halos.
> > Rob Gendler
> > Email: robgendler@att.net
> > Web site: http://www.robgendlerastropics.com/
> > ----- Original Message -----
> > From: "Volker Wendel" <volker@spiegelteam.de>
> > To: <astro-photo@seds.org>
> > Sent: Sunday, September 01, 2002 10:10 AM
> > Subject: Re: [APML] Cederblad 214, NGC 7822
> >
> > > Simply beautiful, Rob!
> > >
> > > How much did you weight the h-alpha image when combining it with the
> > > RGB-channels?
> > >
> > > Volker
> > > www.spiegelteam.de
> > >
> > >
> > >
> > > > Hi all,
> > > > This was taken with the Nikon 300mm lens at F4
> > > > and ST10. Its an h-alpha luminance.
> > > > http://www.robgendlerastropics.com/7822.html
> > > > Higher res crop of cederblad 214 at
> > > > http://www.robgendlerastropics.com/cederblad.html
> > > > Rob Gendler
> > > > Email: robgendler@att.net
> > > > Web site: http://www.robgendlerastropics.com/
> > > >
> > > >
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