Re: [APML] How to build a mosaic?

["Eddie Guscott" <eddie.guscott@blueyonder.co.uk>]

Hi Bobby

Sorry to butt in on the thread, just wanted to say that's the most
awesome pic of the Rosette I've seen. Colour balance in stunning.
Most images I've seen show the central "hole" reddish in colour. Yours
is  black. Fantastic... well done

Eddie Guscott


----- Original Message -----
From: "Bobby Middleton" <bobm@koyote.com>
To: <astro-photo@seds.org>
Sent: Thursday, September 26, 2002 8:51 PM
Subject: Re: [APML] How to build a mosaic?


>
> Hi Nicola.
> Mosaics can be a super way of showing a larger piece of the sky, but there
> are many problem associated with doing them. You have just touched upon
two
> of the problems.
> The first problem is the color balance (and also differences in brightness
> which are similarly fixed). It is best to shoot the adjacent frames while
> they are close to the zenith. Use the same film and try to do the
different
> frames the same night. This will minimize any color shifts due to
elevation,
> light pollution, and other variables. But there will still be some
> differences in color and brightness. These have to be equalized as best as
> possible in Photoshop using curves and levels adjustments. I adjust the
> frames before I combine them. After combining it is still possible to
> equalize the different frames by using selective adjustments and
feathering
> with the lasso tool. The seems may still need blending with the clone
tool.
> The second problem is harder to deal with and had up to a point limited
the
> size of my mosaics. That is the problem of curved fields which will cause
> different frames to warp when joined. Axel Mellinger has a program that he
> used to fix this for his milky way mosaic, but I have since learned that
the
> different frames can be aligned in programs like RegiStar on top of a
single
> wide-field image of the area to be mosaiced. This is what I now do and the
> technique has allowed me to add as many as ten frames from a 2200mm focal
> length newtonian without any major problems from frame warping.
> With constellation mosaics you may have difficulty in getting a wide-field
> image to use for registration. Perhaps there are some large-sized web
images
> that might be used with the author's permission to align your different
> frames. And it may be possible to use certain star mapping programs to
make
> an image to register your frames with.
> Here is my 10 frame Rosette mosaic:
> http://www.koyote.com/users/bobm/rosette2.htm
> Good luck! Mosaics are difficult but a good one is well worth the effort.
> Bobby Middleton
>
> ----- Original Message -----
> From: "Nicola Montecchiari" <nmontec@libero.it>
> To: <astro-photo@seds.org>
> Sent: Thursday, September 26, 2002 2:11 PM
> Subject: [APML] How to build a mosaic?
>
>
> > Hello all,
> >
> > I've got some mily way shots I would like to put together in a mosaic of
> > pictures.
> > The problem is: the colours are different from one shot to another and
> with
> > photoshop it seems impossible to mathc them, or at least i don't know
how
> to
> > do that.
> > And also, stars look like they are in slightly different position like
it
> is
> > not possible to overlap them.
> > Is there any program that cna help me with all those problems above? Or
a
> > web page where it is explained how to do it?
> >
> > Thank a lot!
> > Nicola
> >
> >
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