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Date: 20 Jul 2007 17:09:07
From: Anthony Ayiomamitis
Subject: NGC 6888 - Crescent Nebula in Cygnus
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Dear group,
I have spent the past couple of evenings pursuing the stunning emission
nebula NGC 6888 in Cygnus with mixed results. Although successful at
capturing the plethora of stars in the region (nearly 8000 stars in my
image), I was partially successful in acquiring the dim portions of the
Crescent Nebula.
For last night's result based on just under five hours total exposure,
please see http://www.perseus.gr/Astro-DSO-NGC-6888.htm .... all
comments and suggestions welcome!
Anthony.
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Date: 28 Jul 2007 23:57:46
From: AstroApp
Subject: Re: NGC 6888 - Crescent Nebula in Cygnus
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On Fri, 20 Jul 2007 17:09:07 +0300, Anthony Ayiomamitis
<anthony@no2spam.perseus.gr > wrote:
>Dear group,
>
>I have spent the past couple of evenings pursuing the stunning emission
>nebula NGC 6888 in Cygnus with mixed results. Although successful at
>capturing the plethora of stars in the region (nearly 8000 stars in my
>image), I was partially successful in acquiring the dim portions of the
>Crescent Nebula.
>
>For last night's result based on just under five hours total exposure,
>please see http://www.perseus.gr/Astro-DSO-NGC-6888.htm .... all
>comments and suggestions welcome!
>
>Anthony.
Wonderful picture. I've been happy with the way this object looks to
the eye in my C-11 but of course I don't get the reddish color.
I am aware that you defend the ersatz diffraction spikes on the bright
stars (I don't remember: do you make them with a software algorithm
during processing, or are they acquired by putting threads across your
aperture?)
But I have two comments:
1. I hope if you are doing the diffraction pattern AFTER the raw data
have been acquired, that you are keeping the raw information, sans the
artificial artefact. That way, if some day you change your mind, you
can redo the picture without the diffraction spike effects.
2. The spikes are rather prominent and cover quite an area. This is
sometimes a problem when searching images for latent data in the case
of looking for an unknown object or a change in a known one. I have
had problems with old film and plate halation patterns -- and
diffraction spikes -- covering up areas near bright stars; once I was
searching for a change in a faint star near a bright one, and all
resources I had at my command had such halation and spikes that it was
hopeless to find any old pictures for the purposes of comparison with
a newly-acquired one: the artefacts swamped the faint object.
Just a thought, in case you want to go searching for things. The
other night, in fact, I saw visually a huge, dense pattern of what
LOOKED like nebulosity around 4 Cygni, not plotted in the Uranometria.
I tested this against other stars of the same magnitude in the region
of 10-20 degrees within that star, and none glowed that much. I wrote
to Brian Skiff and asked him; he thought there was nothing unusual and
suspected merely an instrumental artefact, as I had not - by my
admission - been able to measure it instrumentally. I only made
visual comparisons, which are notoriously inaccurate.
Well, Jaakko Saloranta examined the DSS blue plate after heavy
processing, and reports that I probably saw some faint reflection glow
that this plate has recorded.
The problem is: your diffraction patterns would totally mess that up,
so an image done by you in this fashion would not be suitable as a
reference for comparison purposes.
I've argued this til I am blue in the face, but the advocates of "fake
spikes" disagree with me completely, and love 'em. If you want pretty
pictures that SEEM to look like ones done years ago by Malin, with
heavy unsharp masking, then -- sure -- you can generate this effect to
your heart's desire.
But, it seems to me tragic that you have a marvelous imaging device
that itself creates no spikes or internal reflection artefacts -- and
then you ADD them, somehow...why?
AstroApp
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Date: 20 Jul 2007 13:19:03
From: Ben
Subject: Re: NGC 6888 - Crescent Nebula in Cygnus
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> How about the Iris nebula or the Fireworks Galaxy next? ;-)
>
> Anthony.
Either/or..... How about both? I'm sure they will be as
well done as the rest of your captures.
Ben
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Date: 20 Jul 2007 11:29:06
From: Ben
Subject: Re: NGC 6888 - Crescent Nebula in Cygnus
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Anthony,
Well you promised us this one and you certainly made good
on your promise. Fine work!
Ben
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Date: 20 Jul 2007 21:54:02
From: Anthony Ayiomamitis
Subject: Re: NGC 6888 - Crescent Nebula in Cygnus
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Ben wrote:
> Anthony,
Hi Ben,
>
> Well you promised us this one and you certainly made good
> on your promise. Fine work!
How about the Iris nebula or the Fireworks Galaxy next? ;-)
Anthony.
>
> Ben
>
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Date: 20 Jul 2007 08:58:32
From: ianhillsmith@yahoo.com
Subject: Re: NGC 6888 - Crescent Nebula in Cygnus
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On Jul 20, 3:09 pm, Anthony Ayiomamitis <anth...@no2spam.perseus.gr >
wrote:
> Dear group,
>
> I have spent the past couple of evenings pursuing the stunning emission
> nebula NGC 6888 in Cygnus with mixed results. Although successful at
> capturing the plethora of stars in the region (nearly 8000 stars in my
> image), I was partially successful in acquiring the dim portions of the
> Crescent Nebula.
>
> For last night's result based on just under five hours total exposure,
> please seehttp://www.perseus.gr/Astro-DSO-NGC-6888.htm.... all
> comments and suggestions welcome!
>
> Anthony.
Do try it in Hydrogen Alpha - great fun and lots of fine detail to
tease out.
Martin N
http://www.martin-nicholson.info/index.htm
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Date: 20 Jul 2007 19:58:03
From: Anthony Ayiomamitis
Subject: Re: NGC 6888 - Crescent Nebula in Cygnus
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ianhillsmith@yahoo.com wrote:
> On Jul 20, 3:09 pm, Anthony Ayiomamitis <anth...@no2spam.perseus.gr>
> wrote:
>> Dear group,
>>
>> I have spent the past couple of evenings pursuing the stunning emission
>> nebula NGC 6888 in Cygnus with mixed results. Although successful at
>> capturing the plethora of stars in the region (nearly 8000 stars in my
>> image), I was partially successful in acquiring the dim portions of the
>> Crescent Nebula.
>>
>> For last night's result based on just under five hours total exposure,
>> please seehttp://www.perseus.gr/Astro-DSO-NGC-6888.htm.... all
>> comments and suggestions welcome!
>>
>> Anthony.
>
Hi Martin,
> Do try it in Hydrogen Alpha - great fun and lots of fine detail to
> tease out.
My first stab at NGC 6888 was indeed with an h-alpha (Astronomic 13nm)
but I was disappointed at the result following three hours total
exposure (12x15min subs). It is for this reason last night I revisited
an RRGB approach and the results are virtually the same.
I will give it another shot with h-alpha and this time I will pursue a
greater total exposure (ex. five hours).
Anthony.
>
> Martin N
>
> http://www.martin-nicholson.info/index.htm
>
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Date: 20 Jul 2007 09:27:35
From: Pierre Vandevenne
Subject: Re: NGC 6888 - Crescent Nebula in Cygnus
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Anthony Ayiomamitis <anthony@no2spam.perseus.gr > wrote in news:f7qfn2$as$1
@mouse.otenet.gr:
> Dear group,
>
> I have spent the past couple of evenings pursuing the stunning emission
> nebula NGC 6888 in Cygnus with mixed results. Although successful at
> capturing the plethora of stars in the region (nearly 8000 stars in my
> image), I was partially successful in acquiring the dim portions of the
> Crescent Nebula.
>
> For last night's result based on just under five hours total exposure,
> please see http://www.perseus.gr/Astro-DSO-NGC-6888.htm .... all
> comments and suggestions welcome!
Its nice looking as usual, but I believe you could do much better on that
one, including catching the nebular ghosts around NGC 6888 itself, if you
used a H-Alpha filter and used that as luminance. I got a higher level of
signal from a an 10x10min exposure in a poorly collimated 200SS under mag
2.5 skies in Belgium.
Give it a try, the area doesn't lack bright guide stars anyway.
--
Pierre Vandevenne - DataRescue sa/nv - www.datarescue.com
The IDA Pro Disassembler & Debugger - world leader in hostile code analysis
PhotoRescue - advanced data recovery for digital photographic media
latest review: http://www.pcmag.com/article2/0,1759,1590497,00.asp
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Date: 20 Jul 2007 17:46:22
From: Anthony Ayiomamitis
Subject: Re: NGC 6888 - Crescent Nebula in Cygnus
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Pierre Vandevenne wrote:
> Anthony Ayiomamitis <anthony@no2spam.perseus.gr> wrote in news:f7qfn2$as$1
> @mouse.otenet.gr:
>
>> Dear group,
>>
>> I have spent the past couple of evenings pursuing the stunning emission
>> nebula NGC 6888 in Cygnus with mixed results. Although successful at
>> capturing the plethora of stars in the region (nearly 8000 stars in my
>> image), I was partially successful in acquiring the dim portions of the
>> Crescent Nebula.
>>
>> For last night's result based on just under five hours total exposure,
>> please see http://www.perseus.gr/Astro-DSO-NGC-6888.htm .... all
>> comments and suggestions welcome!
>
Hi Pierre,
> Its nice looking as usual, but I believe you could do much better on that
> one,
I agree fully there is much more room for improvement.
> including catching the nebular ghosts around NGC 6888 itself, if you
> used a H-Alpha filter and used that as luminance. I got a higher level of
> signal from a an 10x10min exposure in a poorly collimated 200SS under mag
> 2.5 skies in Belgium.
I did try h-alpha the first night out (Astronomik 13nm) and 12x15min
exposures but the result was not very much different.
>
> Give it a try, the area doesn't lack bright guide stars anyway.
>
This is certainly true and even when imaging in h-alpha.
Anthony.
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