Re: [APML]: Pelican in Tri-Color

["Ian Turner" <skyshooter@mindspring.com>]

The Astro-Photography Mailing List
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Chuck

Sure is alot of work, Chuck it looks great. 
I tried this about 1 year ago and said forget it. I switched my Tri Color
efforts  to CCD and it is still 2 hour effort. 

I commend U for your effort.

Ian
_________________________________________
                Ian Turner              
     Astrophoto and CCD Imaging Tips
http://www.mindspring.com/~skyshooter/                                      
                                                         
_________________________________________

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>From: Chuck Vaughn <aa6g@aa6g.org>
>To: astro-photo@nightsky.com
>Subject: [APML]: Pelican in Tri-Color
>Date: Sat, Jul 18, 1998, 22:15
>

>The Astro-Photography Mailing List
>------------------------------------
>
>Hi All,
>
>I just completed the first tri-color image I have ever done. This was a
>tremendous amount of work. This image is done according to the philosophy
>I wrote about in my article "Color Photography of Emission Line Sources". 
>
>See: http://www.aa6g.org/Astronomy/articles.html
>
>The filter set used is the one shown in the article and was designed to
>meet as much as possible the ideal filter set suggested by Brad Wallis
>and Robert Provin in their book. It's not perfect but it's better than
>any commercial tri-color filter set I know of. The blue and green filters
>both have real response at 500nm.<g>
>
>You can go directly to my astrophoto page at:
>
>http://www.aa6g.org/Astronomy/astrophotos.html
>
>Be sure to click on the large Pelican image to see a comparison between
>tri-color and PPF. This turned out to be most interesting.
>
>But first the image...
>
>The tri-color image was constructed as follows:
>
>Calculations of Tech Pan response with filter responses showed that the
blue
>and red exposures should be about equal times. The green exposure needed to
be
>2 1/4 times as long. This was impractical since I needed to run 3 hours
with
>the red and blue filters. Instead I ran 3 1/2 hours with the green filter
>and stretched the green image twice as much in the Polaroid pre-scan
software.
>I carefully choose the scan setups so that one image was not biased
compared
>to another. Finally I scanned the negatives to preserve the grayscale and
>not block up the color in the nebula.
>
>The negatives are not perfect. The green has some glitches in the upper
left
>corner and the red negative was taken last night and the temperature fell
>a lot during the exposure causing the refractor to shift focus which seemed
>to impact the corners more than anywhere else.
>
>Pelican comparisons....
>
>I compared the tri-color image to the PPF negative that is making the
>rounds in the scanner test. This is a single 90 minute exposure and
>shows the only part of the two images that overlap.
>
>Although some of the stars do show blue halos on the tri-color, overall the
>stars are smaller than on the PPF negative. This was a surprise since I've
>heard so many complaints about bigs stars on AP refractors due to
out-of-focus
>blue light. My blue filter has response well into the near UV while PPF
does
>not. I suspect the blue halo stars are just very blue stars and record
better
>in that exposure. There are big orange stars as well.
>
>Note on monitor settings...
>
>This is related to viewing the images. PS 5.0 instructions for monitor
>calibration say to set the Contrast to maximum and then adjust the
Brightness
>so blacks and whites are balanced. This turns out to be a good thing to do
>as it maximizes the RGB color space of your monitor and images have the
most
>range possible.
>
>Chuck  <aa6g@aa6g.org>
>
>