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Re: (meteorobs) OT: Film for comet photos

It is interesting that some people are using such software packages as 
"photshop".  However, in cometary astronomy, there are two basic problems in 
doing so.  The first is if you manipulate the color of the image, you could 
be losing valuable information.  The color of the comets tail, or coma, or 
even nuclear region are indicative of what parent moecules are being 
released from the nucleus.  The Color response of the film can detect only 
certain molecules, because each and evey molecule can only emit certain 
wavelengths of light, or spectral lines.  So the color response of the film 
is very important.  It is obvious that you do have some understanding of the 
problems with grain.  However, with the newer color films as with the older 
versions, grain is not a factor considered in a color film, since the latent 
image taken upon exposure, is replaced by chemical dyes during the 
development process.  (Reference any Kodak color film manual, or data 
sheet.)  The second problem to manipulating the image is, are you bringing 
out an image that you want to see or is it the image that is really there.  
If you read any book that deals with the conversion of an image from a 
photographic print or negative, or slide (positive), you  expose so that you 
do not expose for the same periods of time that you would if you were just 
after a photographic print.  Sure you can push or pull an image.  But you 
lose imformation.  So how sure are we that the image that you manipulate is 
what was actually there?  Not very sure at all, if you were to study what 
the professional astronomers are saying.  Even they post raw images plus the 
processed image, but they are very seldom manipulating the color.  R. Warren


>From: Mike Linnolt <mlinnolt@alum.mitdot edu>
>Reply-To: meteorobs@atmob.org
>To: meteorobs@atmob.org
>Subject: Re: (meteorobs) OT:  Film for comet photos
>Date: Mon, 09 Jul 2001 19:24:45 -1000
>
>Regarding color balance, this may have been an issue in the past,
>but these days with most photos prepared in digital form for posting
>on websites and so on, the overall color balance of a particular film
>is largely irrelevant. Most image processing application, like
>Photoshop for instance, allows you to adjust the various color
>levels to achieve basically a perfect balance from any raw image,
>as well as enhance every subtle detail.
>
>The real issue is to choose a film with very fine grain, high
>resolution and good reciprocity characteristics. One such film is
>Kodak Royal Gold 200. The 400 speed version is grainier, but still
>can be enhanced to yield a decent image. You can see my result
>with this film of the Comet LINEAR at:
>
>http://www.qsldot net/ah6l/A2_image.html
>
>Its a 5min exposure with normal 50mm lens and shows about 8° of
>tail after processing in Photoshop. The raw image is pretty cruddy,
>I can email it to anyone interested in the comparison!
>
>Mike Linnolt
>Hawaiian Astronomical Society
>
>
>On 9 Jul 2001, at 23:37, C.L. Hall wrote:
>
> > >What is the high speed tungsten film that you use???
> >
> > Kodak Ektachrome 320T.
> >
> > It's a colour slide film, balanced for tungsten light as opposed to
> > daylight.  It is not recommended for meteor work - most meteor work 
>tends
> > to be black and white.  It is also not recommended for comet shots if 
>you
> > want what people accept as realistic colour.
> >
> > Tungsten film is great for copying prints.   Having some in the fridge a
> > number of years back, I decided to try it for astro shots, and found 
>that
> > it tends to work very well for comets.  If you are near a city, it 
>changes
> > the sky tones to blue, and eliminates the awful green and brown skies of
> > light polluted areas.  It tones down moonlight.  It brings out comet 
>tails
> > very nicely, and will pick up tail in situations where daylight films 
>have
> > problems.  The tungsten film is also much more forgiving as regards sky
> > fogging.  With that said, for major comets I will run a number of types 
>of
> > film, both daylight and tungsten balanced.
> >
> > I don't use filters.  I just enjoy pushing the limits of obscure types 
>of
> > film - and comets are one of my favorite subjects.
> >
> > Clear skies,
> > - Cathy Hall
> >    south of Ottawa, Canada
>
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