RE: Re:[APML] orion mosaic

["Lane, Jason R" <jason.lane@navy.mil>]

That's an interesting point, Philip.  The problem I see is that the spectral response of film and silicon is simply different than that of the eye.  With film you can't really do anything.  However, since silicon is silicon is silicon (the detecting material for CCD and CMOS focal plane arrays), you can in theory design a spectral filter for use with the detector which will match the spectral response of the eye.  Then you will truly have what the eye would see if it was much more sensitive.  I believe such filters are available today.

Cheers,
Jason



-----Original Message-----
From: astro-photo-bounces@seds.org
[mailto:astro-photo-bounces@seds.org]On Behalf Of Philip Perkins
Sent: Thursday, March 31, 2005 4:10 PM
To: Discussion of Film Astrophotography
Subject: Re: Re:[APML] orion mosaic


Rob and Wei-Hao,

I agree this is a wonderful wide field composition.  I think there is a lot 
to be said for recording objects in the night sky as the human eye might 
see them if it were thousands of times more sensitive.  For this purpose it 
seems to me that recording an unfiltered image on natural daylight film is 
very acceptable.  In this context use of an Ha filter is probably somewhat 
artificial - after all the human eye does not have an Ha filter stuck in 
front of it.

The use of an Ha filter is the latest in a long line of CCD imaging 
fashions.  Remember that a few years ago an image had to be deconvolved to 
virtual oblivion before it was considered processed properly.  Nowadays 
little or no deconvolution is the norm.  The next vogue was intense star 
colours.  After this came galaxy images pock-marked with intense Ha regions 
that look like a severe case of acne.  We all know that galaxies would 
never look like this naturally if we could be a few million light years 
closer.  Now an Ha filter has to be used if nebulous regions are to be 
considered recorded properly.  This will surely be replaced by some new 
vogue in the future.  Possibly new filtering techniques - I see that OIII 
filters are starting to be used more and more.

These are all admirable methods in trying to achieve something different 
from static celestial objects where, unlike terrestrial objects, the 
lighting and aspect can never change.  But, broadening the mind a little, I 
think there is actually a wide spectrum of other techniques that can show 
different aspects of the night sky.  Although tried and trusted, the purity 
of an unfiltered image on natural daylight film has a certain appeal for 
me, of which this image is a classic example.  The Ha regions seem to be 
very well recorded - besides, Ha is only one aspect - there is a lot else 
going on in this image which notch-filtering of Ha wouldn't help, including 
the Witch Head nebula.

--Philip

At 06:03 31/03/2005 -0500, you wrote:
>Hi Wei-Hao,
>A beautiful rendition of this region. I like the stars and in particular the
>nice compact starfield in the upper left....I haven't seent this before.
>One comment though is the weakness of the h-alpha emission even from
>a dark sky like yours. Really only narrowband h-alpha imaging can bring
>the faint emission out.
>Rob Gendler
>email: robgendler@att.net
>Web Site: http://www.robgendlerastropics.com


Philip Perkins
<ppastro2@astrocruise.com>
Wiltshire UK & Luberon France
www.astrocruise.com


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